The Cutting Edge – blog version

Jolle Kirpensteijn, DVM, PhD, DACVS & DECVS (Small Animal)

Gert ter Haar, DVM, PhD, MRCVS, DECVS (Small Animal)


The third edition of ‘The Cutting Edge, Basic Veterinary Surgery Techniques’ has been prepared by various veterinary lecturers at the Utrecht University Faculty of Veterinary Medicine, the University of Ghent, and the Royal Veterinary College of the London University. Its goal is to teach students the essential art of surgery without having a specific species in mind. This edition is designed for an open-access web-based platform. Students worldwide will be able to use the information for their benefit while improving their surgical knowledge and skills. 

The ‘Cutting Edge 3’ provides veterinary students and new graduates tools to grasp the principles of surgery, along with a discussion of the limitations and complications of surgical procedures. It should not be regarded as a complete reading text for all surgical problems and techniques but merely a basis for the inexperienced surgeon. Other textbooks will be able to provide more advanced techniques. 

Previously published work by Dr. Wim Klein, Dr. Marianne Tryfonidou, Dr. Rien van de Velden, Dr. Peter Stolk, Prof Herman Hazewinkel, Prof Astrid Rijkenhuizen, Dr. Ruud Keg, and Prof Ludo Hellebrekers is updated and expanded. We value their expertise and thank them for their previous work. Mr. Joop Fama is thanked for supplying many of the photographic materials used in this book. The ‘Cutting Edge 3’ is an improvement of the Cutting Edge 2 (2006) and is translated initially from the first edition ‘Leren Opereren’ (2005).

We want to acknowledge the help of Dr. Jos Ensink, Dr. Wim Back, Dr. Herman Jonker, and Dr. Stefan Cokelaere for their support of the equine and production animal sections.

Parts of this publication were previously published on Vetvisuals (, and we would like to thank André Romijn, from Roman House Publishers Ltd and Kathryn Jenner for their support.

 Jolle Kirpensteijn & Gert ter Haar

Chief Editors &

Chapter 1 Clinical problem solving in surgery

Freek J van Sluijs, DVM, PhD, DECVS (Small Animal)

with contributions from

Gert ter Haar, DVM, PhD, DECVS (Small Animal)

Jolle Kirpensteijn, DVM, PhD, DECVS (Small Animal) & DACVS

1.1       Introduction

1.2       Clinical decision-making

1.3       Purpose of surgery in animals

1.4       Methods for cutting or destroying tissue

1.5       Methods to control intra-operative hemorrhage

1.6       Nomenclature

1.7       References

1.1 Introduction

Surgery, literally meaning “handwork” from its Greek origins, is the art of treating a patient for a medical condition by using manual and/or mechanical methods. In doing so, the surgeon attempts to achieve a particular medical outcome. Surgical skills alone are not enough to achieve the intended outcome, and other factors surrounding both the patient and the owner also play an important role. The well-known expression “the operation was a success, but the patient died” may lead one to believe that surgery is purely the act of performing an operation. This, however, is rather short sighted because many more factors (including ethical and economic) are involved in the surgical process before, during and after the operation, which may last weeks to months after the actual procedure itself (Table 1).

Table 1. Factors influencing surgical outcome

Patient-related factors

  • Age
  • Bodyweight and condition
  • Concurrent disease

Surgeon-related factors

  • Skills
  • Training
  • Experience

Practice-related factors

  • Surgical theatre
  • Personnel (surgery and anesthesia)
  • Hospitalization facilities

Client-related factors

  • Education
  • Finances

Age, a patient-related factor, is not, as such, a reason to refrain from surgery, but very young and very old patients present special considerations. Young patients have an increased risk of developing hypothermia and hypoglycemia, whilst geriatric patients may suffer from a subclinical organ dysfunction, which may affect convalescence. Wound healing may be delayed in patients with severe malnutrition and obese patients have a higher risk of complications during and after surgery. Concurrent diseases such as heart disease or renal failure may increase anesthetic risk and should be identified and managed before surgery.

Surgeon-related factors are based around the skills of the surgeon, the level of training and experience with the procedure that will be performed.

Practice-related factors include the surgical theatre (overpressure ventilation, electrical safety, management of hygiene), the personnel (presence of specialists or technicians qualified in anesthesia, adequate surgical assistance) and facilities to hospitalize patients requiring prolonged or intensive care.

Client-related factors are the ability of the client to understand the procedure and instructions for appropriate aftercare, and the willingness or ability to pay for the costs of treatment.

1.2 Clinical decision-making

Clinical decision-making in surgery is primarily focused on the question of whether an operation is the best treatment for the disease concerned. The risks and benefits of an operation must be weighed against the risks and benefits of other therapies. Attention should also be paid to treatments that may support or expand the effect of surgery (physiotherapy, radiation therapy, chemotherapy). Ideally, this assessment is based on the proven efficacy of eligible treatments. In veterinary medicine the cost of treatment is an important factor that must also be taken into consideration. A stepwise approach can help to weigh the costs against the expected results at critical stages in the decision-making process. A diagnostic and therapeutic scenario (or check list) is a detailed description of such an approach. In the scenario all steps of the procedure are described in the sequence in which they should be performed. The scenario may be represented graphically in an algorithm or flow sheet.

Diagnostic and therapeutic scenarios are based on evidence from clinical trials and are developed by scientific professional organizations with input from scientists and practicing veterinarians. When a professional organization has published a scenario, it should be binding for all professionals. Disciplinary judges will use the scenario as a standard for professional conduct to which the action of veterinarians is compared.

Unfortunately, evidence-based scenarios are still rare in veterinary medicine. But in the absence of formal scenarios, veterinary surgeons may develop their own algorithms. An example is given in Figure 1, which shows an evidence-based scenario for the diagnosis and treatment of anal sac carcinoma in the dog.

The algorithm starts after an anal sac adenocarcinoma has been diagnosed by fine needle aspiration biopsy. Additional tests are undertaken (chest X-ray or CT, abdominal ultrasound) to stage the disease. A stepwise approach is followed to ensure that each decision is based on a realistic expectation of the results that can be achieved. These are derived (for this example) from two clinical studies that describe survival in 113 and 130 dogs with anal sac carcinoma.1, 2 In these studies, survival was correlated to the clinical stage with median survival times ranging from 2 (stage 4) to 40 months (stage 1). The algorithm illustrates that in advanced stages more treatment modalities are necessary to obtain shorter survival times. The expected survival may help to balance the costs of treatment against the outcome. The algorithm also depicts the sequence in which decisions are made.

Stage 1 is the simplest situation: a small tumor without regional or distant metastasis. Treatment consists of one modality (resection of the tumor) and is expected to produce good long-term results. In stage 2 the tumor is large (> 10 cm2) but there are no regional or distant metastases. If the tumor cannot be removed it may be treated by radiation to reduce the size until it has become resectable. Life expectancy after treatment is less than in stage one, but still acceptable. Stage 3 is characterized by regional metastases from a small or large tumor. If the metastases are resectable, they will be removed; the same applies to the primary tumor. Radiation therapy will be used preoperatively or intra-operatively if the metastases or the tumor are too large for removal or postoperatively. When their size has been reduced sufficiently, the tumor and the metastases are resected. The costs in this scenario increase with the number of treatments, whilst the life expectancy decreases to half of that in stage 2. In stage 4, the disease has spread to distant sites. Life expectancy is short, and treatment is mainly palliative.

The advantage of the algorithm is that it provides insight into the costs and benefits of treatment in various stages of the disease. This helps the veterinarian and the owner to balance these aspects. The algorithm’s limitation is that it displays median survival of a group of patients – individual patients may have a longer or shorter survival. One should be aware of this limitation when using algorithms. 

Figure 1. Diagnostic and therapeutic algorithm for anal sac carcinoma in the dog 

An important aspect in the anal sac adenocarcinoma example is the assessment whether the tumor (or the lymph node) is resectable. In general, tumors are resectable if they can be removed with safe margins without causing damage to nearby vital structures (Figure 2). In the anal sac adenocarcinoma example, nearby vital structures are the external anal sphincter and the pudendal nerve. The close proximity of the sphincter to the anal sac excludes resection with wide margins; however, the tumor is resectable if it can be removed with narrow margins without causing severe damage to the sphincter. Vital structures near enlarged lymph nodes may include the rectum and colon, the urinary bladder, prostate and ureters, the aorta and the external and internal iliac arteries.

Figure 2. Removal of a tumor in the anal sac with safe margins

Before asking whether or not the tumor is resectable, the surgeon must assess whether the patient is operable. The American Society of Anesthesiologists has developed a qualification system for the physical status in human patients that is also used in veterinary medicine. Patients are divided into 5 classes:

Table 2. ASA classification of anesthetic risk[*]

I           A normal healthy patient

II         A patient with mild systemic disease

III        A patient with severe systemic disease

IV        A patient with severe systemic disease that is a constant threat to life

V         A moribund patient that is not expected to survive without the operation

Patients in category I-IV are usually operable, provided that sufficient knowledge, experience and equipment are available to deal with complications. In group V, there is little choice, but this category may be decreased to a lower grade by providing adequate supportive therapy. An example of this is hyperkalemia in a cat with urethral obstruction. If a catheter can be inserted, fluid therapy may move the patient from category V to category IV or III and reduce the risk of cardiac arrest and other problems during surgery and anesthesia. 

1.3 Purpose of surgery in animals

  1. Prophylactic surgery: for instance, to prevent neoplastic disease, e.g., ovariectomy (OVE) for mammary gland tumors, excision of actinic dermatitis from the auricle or nasal plane for squamous cell carcinoma (SCC), and castration for cryptorchid testicles.
  2. Therapeutic surgery: in the treatment of e.g., wounds, lesions, inflammation, anatomical changes, tumors
  3. Palliative surgery: to improve but not completely cure the disease that the animal is afflicted with (e.g., debulking surgery)
  4. Diagnostic: e.g., biopsy, operations which reveal a disease (like endoscopic exploratory surgery or an exploratory laparotomy)
  5. Surgery to increase the animal’s utility for certain purposes: e.g., castration, dehorning
  6. Experimental surgery for biomedical research

1.4 Methods for cutting or destroying tissue

  1. Cutting with sharp instruments
  2. Cutting or destroying tissue using high frequency currents: electrosurgery (‘electric knife’) and radiosurgery
  3. Destroying tissue by freezing (and thawing): cryosurgery or cryonecrosis
  4. Destroying tissue by the direct application of hot metal or by chemicals: cauterization
  5. Localized thermal effect using Light Amplification by Stimulated Emission of Radiation (‘laser’ surgery)
  6. Ultrasonic ablation: e.g., Ultrasonic Surgical Aspirator (CUSA)
  7. Controlled ablation (coblation)
  8. Cutting with radioactive devices (focused radiation therapy including gamma knife)

The latter three devices are rarely available for general veterinary practice due to costs but can be used in specialized (university or private practice) clinics or research facilities. Methods 1-5 will be discussed in length in the upcoming chapters.

1.5 Methods to control intra-operative hemorrhage

  1. Pressure
  2. Mechanical devices (sutures, clips and ties)
  3. Coagulation devices
  4. Laser devices
  5. Sealing devices (e.g., the LigaSure, ENSEAL)
  6. Drug carrying devices, e.g., gel foam or biomatrix

1.6 Nomenclature

The best way to name operations is to use a combination of anatomical terms and Greek suffixes, thereby describing the location and type of operation. Exceptions are operations named after the inventor or surgeon. Examples:

–tomy (cutting):

  • thoracotomy: opening the thorax
  • gastrotomy: incising the stomach

–stomy (making an opening):

  • colostomy: making an artificial opening of the colon on the surface of the abdomen
  • gastroduodenostomy: creating an anastomosis between stomach and duodenum

–ectomy (excision):

  • splenectomy: removing the spleen
  • ovariohysterectomy: removing the uterus and the ovaries
  • ovariectomy: removing the ovaries
  • orchidectomy: removing the testicles (castration)

–plasty (shaping, forming):

  • episioplasty: reconstruction of the vulva

–centesis (perforating or draining):

  • paracentesis: penetrating a body cavity for the aspiration of liquid
  • cystocentesis: penetrating a urinary bladder for the aspiration of liquid

–pexy (attaching):

  • gastropexy: attaching the stomach to the abdominal wall to prevent torsion (volvulus)
  • colopexy: attaching the colon to the abdominal wall to prevent a rectal prolapse

–rrhaphy (suturing or closing):

  • inguinal herniorrhaphy: suturing an inguinal hernia
  • diaphragmatic herniorrhaphy: suturing a diaphragmatic hernia
  • perineal herniorrhaphy: suturing a perineal hernia
  • temporary tarsorrhaphy: temporarily suturing upper to lower eyelid

It should be noted that the field of surgery extends beyond the surgical procedure alone. Many other therapeutic modalities are used too, such as wound dressings, pharmacotherapy, radiation- and physiotherapy, etc.

1.7 References

1. Williams LE, Gliatto JM, Dodge RK. (2003) Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995). Journal of the American Veterinary Medical Association, 223(6):825–31

2. Polton GA, Brearley MJ. (2007) Clinical stage, therapy, and prognosis in canine anal sac gland carcinoma. Journal of Veterinary Internal Medicine, 21(2):274-80

3. and (not peer-reviewed documents)

[*] The original qualification has a sixth category that is not applicable to veterinary medicine: a brain-dead patient whose organs are removed for donor purposes.

1.8 CVs of Authors

Prof. Frederik Johan van Sluijs was born in 1947 in The Hague and received his DVM from the Faculty of Veterinary Medicine, Utrecht University, in 1974. Freek did a rotating internship and residency in anesthesiology and clinical care and finalized his Ph.D. in Gastric Dilation-Volvulus in the Dog at Utrecht University. After his assistantship at the Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, he became a full professor in 1990 until 2012. He was Vice-Dean Faculty of Veterinary Medicine, Director Bachelor & Academic School of Veterinary Medicine, and Head of Department Clinical Sciences of Companion Animals at Utrecht University. He became Deputy Professor of Companion Animal Surgery at the Klinik für Kleintierchirurgie, Vetsuisse Faculty, the University of Zürich, in 2012 until 2015. He was a founding member and President of both the EBVS and the ECVS. Email:

Dr. Gert ter Haar is from the Netherlands and studied veterinary medicine at the Faculty of Veterinary Medicine in Utrecht. He graduated in February 1997 with differentiation in Small Animal Medicine and Surgery. After having worked for a few months in private practice, Gert accepted a Clinical Rotating Internship position at the Department of Clinical Sciences of Companion Animals at the Utrecht University, followed by a Residency in Small Animal Surgery from September 1998 – September 2001 in the same Department. In September 2001, he became Assistant Professor in Veterinary Surgery at the university where he trained, dealing mainly with Ear-, Nose- and Throat (ENT) and upper airway diseases. In July 2002, he passed the surgical specialist certifying examination held in Vienna and became a Diplomate of the European College of Veterinary Surgeons. He then became Head of the Department of ENT at the University of Utrecht in February 2003. Also, in 2003 he became the secretary of the International Veterinary Ear, Nose and Throat Association (IVENTA), a specialist association affiliated with the World Small Animal Veterinary Association (WSAVA). His research on hearing in dogs led to his Ph.D. thesis, a 220-page book entitled “Age-related hearing loss in dogs.” in 2009. On the same day, he became President of the IVENTA and the representative of the IVENTA to the WSAVA. He gave over 200 national and international lectures on ENT medicine & surgery, hearing research in dogs, and soft tissue/reconstructive surgery in dogs and cats. He joined the Royal Veterinary College’s surgical team in London, the United Kingdom, in September 2011, where he is working as a senior lecturer in soft tissue surgery and head of the ENT department and ENT, Audiology and Brachycephaly clinics. In 2017, Gert started working in private practice for Anicura in Utrecht, The Netherlands. His current research involves a hearing loss in dogs and cats and brachycephalic obstructive airway syndrome.

Dr. Jolle Kirpensteijn graduated from the Utrecht University Faculty of Veterinary Medicine, Holland in 1988 and finished an internship in small animal medicine and surgery at the University of Georgia in the United States of America in 1989. After his internship, he completed his residency training in small animal surgery and a master’s degree at Kansas State University, USA. The residency was followed by a fellowship in surgical oncology at the Colorado State University Comparative Oncology Unit, USA. In 1993, Jolle returned to Europe to accept a surgical oncology position and soft tissue surgery at Utrecht University. In February of 2005, he was appointed Professor in Surgery at the University of Copenhagen and in August 2008 Professor in Soft Tissue Surgery at Utrecht University. Jolle is a Diplomate of the American and European College of Veterinary Surgeons. Jolle received the title Founding Fellow in Surgical Oncology (2012) and Minimally Invasive Surgery (Small Animal Soft Tissue) (2017) of the American College of Veterinary Surgeons (ACVS). In September 2013, Jolle accepted the Chief Professional Relation Officer position at Hills Pet Nutrition in the USA. Here, he played an integral role as the interface between the company and the profession at large. In 2018, he was promoted to the Chief Professional Veterinary Officer position in the US, where he leads all professional activities in the United States. Jolle has published over 100 peer-reviewed articles, given more than 250 lectures worldwide, and has received the prestigious BSAVA Simon Award in 2007, Hills Voorjaarsdagen Excellence in Healthcare Award in 2009, WSAVA President’s Award, and honorary membership to the Netherlands Association of Companion Animal Medicine (NACAM) in 2017. His main clinical and research interests are professional social media and digital innovations, surgical oncology, and endoscopic & reconstructive surgery. Check out his podcasts at and

Chapter 2: Principles of asepsis, disinfection and sterilization

Gert ter Haar, DVM, PhD, Dipl ECVS (Small Animal)

Jos Ensink, DVM PhD, Dipl ECVS (Equine)

F. Herman Jonker, DVM PhD, Dipl ECAR, Dipl ECBHM

2.1    Introduction                                                                                                                             

2.2    Asepsis

2.2.1    Introduction                                                                                                                        

2.2.2    Rules for aseptic techniques                                                                                               

2.3    Sterilization                                                                                                                              

2.3.1    Introduction                                                                                                                        

2.3.2    Cleaning                                                                                                                              

2.3.3    Wrapping                                                                                                                            

2.3.4    Steam and heat sterilization                                                                                                

2.3.5    Filtration                                                                                                                             

2.3.6    Radiation                                                                                                                             

2.3.7    Chemical sterilization                                                                                                         

2.3.8    Gas plasma                                                                                                                          

2.4    Antiseptics and disinfectants                                                                                                  

2.4.1    Aldehydes                                                                                                                           

2.4.2    Alcohols                                                                                                                              

2.4.3    Chlorhexidine                                                                                                                     

2.4.4    Iodine compounds                                                                                                              

2.4.5    Phenols                                                                                                                               

2.4.6    Quaternary ammonium compounds                                                                                   

2.4.7    Others                                                                                                                                 

2.5    Sterilization indicators                                                                                                            

2.6    Preparing the operation                                                                                                         

2.6.1    Preparing the patient                                                                                                           

2.6.2    Preparing the surgeon

2.6.3   Operating gowns

2.6.4   Gloves

2.6.5   Draping the sterile field

2.7    References and recommended reading

2.1 Introduction

Wound infections are common, potentially serious and often expensive complications of surgery. Around 3-5% of all companion animals undergoing an operation will develop post-operative wound (or surgical site) infections in spite of extensive measures limiting bacterial contamination during surgery and the widespread use of antibiotics (Figure 1). The impact of these infections may vary from minor and rapidly overcome by the animal’s immune system, to life threatening with disastrous consequences.

An understanding of all of the factors that play a role in the origin of wound infection is essential, particularly since the number of (surgical) procedures under anesthesia in patients with a high risk of postoperative infections continues to increase. The issue of antibiotic-resistant micro-organisms has also become a serious problem in veterinary medicine, as these drugs can no longer be relied upon as a solution for every surgical infection. In this regard, strict adherence to aseptic techniques to minimize wound contamination and prevent infection are still the mainstays of successful surgery.

Figure 1. Clinical signs of inflammation are present after prescrotal orchidectomy (castration) in a dog. The classic signs include redness, swelling, pain and heat.

This chapter will cover the principles of asepsis as well as disinfection and sterilization. Chapter 6 will further discuss surgical infections, antimicrobial prophylaxis and the treatment of surgical infections.

2.2 Asepsis

2.2.1 Introduction

Asepsis describes the condition in which living pathogenic micro-organisms are absent. Aseptic techniques can be defined as those methods and actions that achieve asepsis and thus prevent wound contamination during surgery. This not only includes appropriate preparation of the surgical environment, but also the surgical site itself, the operating team and the surgical instruments. In order to achieve this, it is important to work with and adhere to a strict aseptic protocol. It is impossible to eliminate all micro-organisms from the surgical site and the surgical field; however, an aseptic technique will limit the exposure of the patient to low numbers of micro-organisms which are not harmful under normal circumstances.

The most common terms used in the area of asepsis, disinfection and sterilization are defined in Table 1.

Surgical infectionsInfections that develop in the operating site within 30 days after surgery. In the case of surgical implants, infections developing within one year of surgery are considered as surgical infections.
AsepsisThe absence of pathogens in living tissue
Aseptic techniqueMethods and actions that achieve asepsis and prevent contamination during surgery
SterilizationThe process of destruction of all micro-organisms through chemical or physical means such as heat and radiation
DisinfectantsChemical compounds that destroy pathogens on inanimate objects, but do not necessarily inactivate all viruses and bacterial spores
DisinfectionThe use of germicidal compounds on inanimate objects
AntisepsisThe use of antimicrobial chemicals on living tissue. Some antiseptics are diluted forms of disinfectants that may be used on tissue without causing damage.
Table 1. Commonly used terms in the fields of asepsis, disinfection and sterilization

2.2.2 Rules for aseptic techniques

Working with disinfected or sterilized instruments at the start of an operation is no guarantee for contamination-free surgery. In order to ensure that the instruments used, and the wound remain sterile, a number of rules must be observed. These rules ideally should be laid down in a standard operating protocol (SOP) for each operating room (OR). The main rules are:

  • Members of the surgical team must stay within the sterile field at all times.
  • Talking during an operation should be limited to a minimum, as talking causes the release of moisture droplets loaded with bacteria.
  • Movements in the OR should be restricted and minimalized as movement creates air turbulence which may cause contamination. This also means that only those people who are strictly necessary for the procedure should be present in the OR.
  • All material should be sterilized and only handled by ‘scrubbed’ team members, and vice versa – ‘scrubbed’ team members should only handle sterile material.
  • When there is doubt about the sterility of material or a tool, it should be considered contaminated.
  • Operating tables are considered sterile only on table-top level; everything that hangs over the edge is to be considered as contaminated since the surgeon cannot control what happens to it.
  • Operating gowns are sterile when they are unwrapped, but once donned, only the following areas are considered sterile: from hip level to mid-thorax and from the gloved hand to about 10 cm above the elbow. In large animal surgery, extra care should be taken to keep the gown sterile higher up the arm.
  • Sterile objects presented in a broken or wet wrapping should be considered contaminated or not sterile.

2.3 Sterilization

2.3.1 Introduction

A complete destruction or elimination of vegetative bacteria, bacterial spores, viruses, prions, fungi and fungal spores can be achieved by physical or chemical sterilization. Critical (surgical instruments, implants, needles, etc.) and semi-critical items (items that come into contact with mucosa and skin, e.g. endoscopic equipment) should be subjected to sterilization. Physical sterilization includes the use of heat (steam/thermal energy is the most commonly used method in veterinary practice), filtration and radiation (mainly used in the industrial preparation of sterile material). Ethylene oxide is the most commonly used means of chemical sterilization, but physical sterilization is considered more reliable. Cold sterilization refers to the process of soaking instruments in a potent disinfectant such as glutaraldehyde or hydrogen peroxide. Thorough cleaning should precede all methods of sterilization.

2.3.2 Cleaning

Organic and inorganic (cement, glue, carbon deposits) debris must be removed from instruments prior to sterilization as they can lead to corrosion and rusting of instruments, prevent contact of the sterilant with the item’s surface, and can lessen the effectiveness of an agent as a result of chemical reactions with the disinfectant. Since debris is difficult to remove once dried, the first step of the cleaning process after using the instruments is immersion in a disinfectant or a soak in cool water. Cleaning itself can be done by hand (especially delicate instruments) or in a dishwasher (washer decontaminator or sterilizer); the latter method also includes thermal disinfection (Figure 2). While manual cleaning is cheaper, it is less efficacious and the cleaning tools used, brushes in particular, are a potential source of contamination and therefore need to be sterilized or disinfected prior to use. Chemicals used during washing up should be well rinsed in order to avoid a chemical interaction with products used at a later stage. The cleaning of instruments may also be carried out with an ultrasonic cleaner. Before wrapping and sterilization the surgical equipment has to be dried properly, preferably with filtered, medical grade compressed air.

Figure 2. Cleaning can be done by hand (especially delicate instruments) or in a dishwasher (washer decontaminator or sterilizer).

2.3.3 Wrapping

The wrapping and instrument packing area should be a clean and controlled environment, only visited by trained personnel. Instruments with hinges should be opened maximally and packs not too densely packed in order to maximize the surface area for contact with the sterilizing agent. The wrapping material used for the instruments to be sterilized should satisfy the following criteria:

  • it should be permeable to the sterilizing medium
  • it should protect against contamination once sterilized
  • it should be easy to open, but this should not happen without visible damage to the wrapping

The most commonly used wrapping materials are paper, laminate pouches and stainless-steel drums or cassettes. Instruments should be packed in such a way that they are protected from damage and cannot perforate the wrapping material. Dry paper is an excellent barrier against bacteria (Figure 3). In order to limit the risk of contamination through damage, a double layer is used. This double layer also allows sterile unwrapping: an assistant opens the outer layer whilst the operating team opens the sterile inner layer. Laminate pouches are a combination of transparent foil and paper. The advantage of these pouches is that the content is clearly visible. Other forms of wrapping include closed drums, containers and cassettes. Closed drums are unsuitable for sterilization in an autoclave, as the steam cannot pass through the drum; cassettes and containers have vents or filters, which allow the passage of steam. Inside the container is an inner layer of wrapping material, usually paper, which can be used after unwrapping as a sterile cover for the instrument table. Closed drums may be sterilized in a dry-heat sterilizer.

Figure 3. Dry paper is an excellent wrapping material for surgical packs.

The wrapping material must have or be fitted with an indicator which changes color at the correct sterilization temperature or chemical contact and shows whether or not the product has been sterilized (see 2.5 for sterilization indicators). Once sterilized, packages should be properly labelled (type of instrument, sterilization date, expected expiration date and initials of person performing the sterilization procedure) and stored in an airflow-, temperature- and humidity-controlled environment.

2.3.4 Steam and heat sterilization

Dry heat kills micro-organisms through a combination of oxidation and dehydration (a relatively lengthy process and not suitable for certain material such as textiles, rubber and silicone tubes), whilst moist heat kills through coagulation and denaturation of cellular protein. Water catalyzes this process and allows for sterilization at lower temperatures compared to dry heat sterilization. The time of exposure and the temperature needed to kill bacteria depend on their individual sensitivity to heat, which in turn depends on the type of organism and the environment to which it has adapted. Bacterial spores, for example, are much more resistant than the bacteria themselves. Pressure, too, is an important parameter. If steam is kept in a closed compartment (moist heat; autoclave), an increase in pressure will result in an effective increase of temperature. If the exposure to steam at a specific temperature and pressure is long enough, the content will become sterile. As a rule of thumb, a time of 15 minutes at a temperature of 121 °C and a pressure of 2 atmospheres is sufficient to kill even the most resistant micro-organisms and will sterilize all contents of an autoclave (steam sterilizer). Higher temperatures allow a shorter exposure time; for example, at 134 °C, only 4 minutes is necessary. Textiles and rubber or silicone tubes may be sterilized at 121 °C, whilst metal instruments are usually sterilized at 134 °C.

The term autoclave literally means ‘self-closing’: the door of the sterilization chamber is kept closed by the pressure inside. Different types are available, but gravity displacement and pre-vacuum autoclaves are the most common in veterinary practice. Gravity displacement autoclaves are most frequently used. The action mechanism of this sterilizer is based on the principle that air is heavier than steam. The steam is forced into the chamber under pressure and surrounds the material, pushing the air downward, where it can exit through a heat sensitive vent until all air is replaced by steam. In pre-vacuum sterilizers, the air is actively pumped out of the chamber, thereby creating a vacuum, after which steam is injected into the chamber. This allows for shorter sterilization times, but this type of sterilizer is more expensive.

2.3.5 Filtration

Sterilization by filtration is a technique often used for the air supply in the OR (laminar flow ventilation); however, liquids may also be filtered and cleared of micro-organisms and particles.

2.3.6 Radiation

Sterilization using ionizing radiation (e.g. Cobalt 60 or gamma) is used for material that is sensitive to heat or chemical sterilization, such as suture material, swabs and disposable operating gowns. Due to its high cost, this technique is often limited to industrial use and not suitable for veterinary practice. Even though radiation may be suitable for materials, which do not tolerate heat, it may change the composition of certain material (plastic, bone grafts) and drugs. Finally, the use of radiation units is associated with significant safety regulations and radiation is considered to be environmentally unfriendly.

2.3.7 Chemical sterilization

Ethylene oxide is the most commonly used product for chemical, low-temperature sterilization. Ethylene oxide is a colorless and odorless gas with a high capacity of penetration and can thus rapidly penetrate permeated wrapped material and objects to be sterilized. This technique is recommended only for objects that cannot be sterilized by steam. Ethylene oxide is extremely toxic, and objects sterilized by this means must be aired thoroughly before use.

Ethylene oxide is an alkalizing agent that kills micro-organisms through the denaturation of protein, DNA and RNA, and is effective against vegetative bacteria, spores, fungi and viruses. It is supplied as a gas mixture with a carrier gas (usually carbon dioxide or hydrochlorofluorocarbon) in order to reduce its inflammability; mixed with air or oxygen it is highly explosive and inflammable.

Sterilization with ethylene oxide is also influenced by the concentration of the gas, temperature, humidity and exposure time. Doubling the concentration of the active substance will halve the time needed; whilst the activity against organisms will double with every 10 °C increase. The optimal temperature lies between 50 and 60 °C. The humidity should not increase too much, as the interaction between ethylene oxide and water may lead to undesirable condensation products which may damage material such as rubber and plastic. The optimal humidity lies between 20 and 40%.

After sterilization with ethylene oxide, materials need to be well aired to permit the evaporation of absorbed chemicals, as residues of ethylene oxide may be harmful to living tissue. A minimum airing time of 7 days in a well-ventilated area is generally recommended. This time may be reduced to 12-18 hours if a special aeration chamber (aerator) is used.

As with all chemical products, care should be taken when handling ethylene oxide as exposure to this substance may cause irritation to the skin and mucous membranes, nausea and vomiting. In addition, there are safety concerns regarding carcinogenic, mutagenic and neurologic effects.

2.3.8 Gas plasma

Gas plasma sterilization is a relatively new, low-temperature sterilization method without known health risks, and is suitable for heat- or moisture-sensitive instruments. This technique makes use of reactive ions, electrons and neutron particles for sterilization. An aqueous solution of, for example, hydrogen peroxide is injected into a chamber, where it is transformed by electromagnetic energy into a reactive ionized plasma phase, which interacts with micro-organisms. In this way, instruments may be sterilized at a relatively low temperature (approximately 50 °C) and within a short time, after which they may be used immediately as no aeration is necessary. Gas plasma is unsuitable, however, for liquids or objects made from vegetable fibers, such as paper, linen and flexible scopes, as these materials absorb hydrogen peroxide and thereby inhibit sterilization.

2.4 Antiseptics and disinfectants

Antiseptic chemicals are intended for use on living tissue, whilst disinfectants are used on non-living materials only as they often cause tissue damage. A certain substance may have an antiseptic action at low concentrations; whilst high concentrations may act as a disinfectant and be toxic to tissue.

2.4.1 Aldehydes

These substances are used for cold sterilization, but due to their antimicrobial action are also, and in particular, used as disinfectants. Glutaraldehyde is effective against a wide range of micro-organisms, including bacteria (even spores after sufficient exposure), viruses and fungi. The antimicrobial activity is increased in alkaline solutions, but the high pH also increases the polymerization speed of glutaraldehyde, thereby shortening its shelf life. The substance is therefore supplied as an acid solution, and is activated prior to use by adding an activator, which turns it into an alkaline solution. This mixed solution should be used within 2 weeks.

The antimicrobial activity increases with a higher environmental temperature but decreases in the presence of organic material. This is why the tools or surfaces to be disinfected should be thoroughly cleaned first with a sterile saline solution. The exposure time of glutaraldehyde should be at least 20 minutes.

Glutaraldehyde is extremely irritating to skin (use gloves!) and other tissues and can therefore only be used for disinfection and sterilization, not for antisepsis. When using glutaraldehyde, there should be adequate ventilation or extractor hoods for the exhaust of toxic fumes.

Glutaraldehyde is not corrosive and is suitable for the sterilization of delicate instruments with small lenses, such as endoscopes. Prior to use, such instruments should be thoroughly rinsed with sterile saline to remove any remaining glutaraldehyde. Since safer alternatives are available, the use of glutaraldehyde is decreasing in veterinary medicine.

2.4.2 Alcohols

Alcohols are widely used in veterinary practice, although they are only effective against certain vegetative bacteria (through protein denaturation and interference with the metabolism and lysis of cells) and have a poor action against spores, fungi and viruses. They are mildly degreasing, are inactivated by organic debris and have no residual action after evaporation. Ethyl alcohol and (iso)propyl alcohol are the most efficient skin antiseptics with the least side effects. Ethanol (= ethyl alcohol) is commonly used at a concentration of 70 to 80%. This allows a very rapid and effective reduction in pathogens, and the resident flora is also reduced considerably. Isopropyl alcohol reportedly has a higher bactericidal but lower virucidal activity then ethyl alcohol, but is also a more effective fat solvent, limiting its potential use on the skin.

2.4.3 Chlorhexidine

Chlorhexidine diacetate (a solution) and chlorhexidine gluconate (a scrub preparation) have a rapid and lasting action against bacteria, including methicillin-resistant Staphylococcus strains, but a variable and inconsistent efficacy against viruses and fungi. Chlorhexidine exerts a bacteriostatic effect in low concentrations (0.05%-2%) by binding to the protein of the stratum corneum of the skin. In higher concentrations (2%-4%) it causes coagulation of cellular contents, creating a bactericidal persisting residue, killing any bacteria that may emerge from the sebaceous glands or hair follicles during the operation. This makes the substance highly suitable as a disinfectant for surgeon’s hands.

Chlorhexidine has a low toxicity when used as a skin cleaner or as an aqueous solution for wound asepsis, rinsing of the mouth or the mucosa of the urinary tract. Even though it may be toxic for fibroblasts in vitro, rinsing with diluted chlorhexidine has no negative effects on wound healing. The lowest known bactericidal concentration (0.05%) of chlorhexidine diacetate (0.05%), when used intra-articular, however, may cause synovial ulceration, inflammation and fibrin accumulation in some species, and should be avoided. Chlorhexidine is noted to be neurotoxic and ototoxic and can cause ocular damage in higher concentrations.

2.4.4 Iodine compounds

Inorganic iodine has a very wide antimicrobial range when compared to other substances. It kills bacteria, fungi and viruses, but efficacy against spores is dependent on a prolonged contact time. It is active at low concentrations to these organisms, which do not develop resistance to the iodine compounds.

Less desirable properties of iodine are its odor, tissue irritability, staining and corrosiveness. Iodophors are complexes of inorganic iodine and a carrier substance, such as polyvinyl-pyrrolidone (PVP), which together create povidone-iodine (as used in Betadine solution and shampoo). This complex has the bactericidal action of iodine but lower tissue irritability and staining properties. The iodine in this compound, however, is strongly bound, which may make the standard 10% solution insufficiently bactericidal. Dilution of this standard solution will lead to the release of more free active iodine and a higher bactericidal action. The skin should be thoroughly cleaned prior to iodine application as organic debris may reduce the bactericidal action of iodine. Washing with a povidone iodine solution should take several (at least two) minutes in order to allow the release of sufficient free iodine. The toxicity of iodine compounds is low, although individual hypersensitivities (mainly adverse skin reactions as erythema, oedema, papules and wheals) may exist. Iodine has some residual activity.

2.4.5 Phenols

Phenol, cresol and other coal tar derivates, such as hexachlorophene, are generally considered inferior to chlorhexidine and povidone iodine. Hexachlorophene has a relatively slow action but a prolonged residual activity, and its effect is not hampered by organic material. Its inactivation by alcohol and proven neurotoxicity make it unsuitable for practical use.

2.4.6 Quaternary ammonium compounds

Quaternary ammonium compounds, such as benzalkonium chloride, are cationic surfactants that dissolve lipids of bacterial cell walls and membranes. However, they are not effective against viruses, spores and fungi and are inactivated by organic debris and by soaps.

2.4.7 Others

Hydrogen peroxide is used to clean highly contaminated wounds, but it is a poor antiseptic. It is particularly effective against spores, but the 3% and higher concentrations may cause tissue damage. Hydrogen peroxide is also used to improve the cleaning of instruments in combination with an alkaline detergent.

Parachlorometaxylenol and triclosan have no obvious advantages over the commonly used antiseptics in veterinary practice. Triclosan is currently also used in certain suture materials (e.g. Vicryl-plus®). It has broad bacteriostatic properties but is less effective than chlorhexidine and povidone-iodine; its residual effect is intermediate between these products.

Polyhexanide (PHMB), a polymeric biguanide and cationic preservative, inhibits the growth of microorganisms and aids in the removal of dirt and debris from chronic wounds. It is commonly used as an antiseptic in chronic and burn wounds in people, but studies in animals are currently lacking. It has less toxicity on primary human fibroblasts and keratinocytes then other topical antiseptics.

2.5 Sterilizing indicators

The simple placing of materials or objects in a sterilizer and switching on the machine are no guarantee that the end product is indeed sterile. Failure to obtain a sterile product may be caused by insufficient cleaning, mechanical malfunction of the system, inappropriate use of the sterilizer or the incorrect wrapping of the instruments. The use of sterilizing indicators enables evaluation of the effectiveness of the sterilization. Indicators undergo a chemical or biological change due to the combination of temperature and exposure time.

Chemical indicators, which are available for steam, gas and plasma sterilization often consist of paper strips or tape that have been impregnated with a substance that changes color after reaching a certain temperature. It should be noted that this technique only measures one criterion (temperature) but gives no information about the duration of exposure. For this reason, some autoclaves are fitted with temperature-time writers, which register both the temperature and exposure time (physical indicator).

The use of biological indicators is the surest way to assess sterility. A strain of highly resistant, non-pathogenic, spore-forming bacteria (Geobacillus stearothermophilus for steam, Bacillus atropheus for ethylene oxide) can be added in a small glass container or on a paper strip. After sterilization, the content of the container or strip is cultured; in the case of growth, the sterilization was insufficient.

For both methods, the indicators should be placed in several locations in the sterilizer (e.g. in the center, in a corner or on the outside of an instrument) as the conditions within the sterilizer are not necessarily identical everywhere.

2.6 Preparing the operation

Complications arising after the surgical intervention may often be reduced or even prevented by the correct preparation of the surgeon and the patient. The skin of both the surgeon and the patient is colonized with transient and resident pathogens present in the environment (see 2.6.2 on preparing the surgeon). The skin of the patient normally forms a barrier against environmental pathogens, but this barrier is broken during surgery. The surgical environment, the surgeon and the patient are prepared in order to remove transient flora and reduce the number of resident florae so as to minimize the number of bacteria that may contaminate the wound during the operation. This section will deal specifically with the preparation of the patient and the surgeon, although the design of the OR should also be taken into consideration.

2.6.1 Preparing the patient

Most companion animals that need to undergo an operation are reasonably clean, but pets that spend much time outdoors and large animals kept in stables may need to be washed in order to clean off dirt and to reduce the bacterial population of the skin and coat. The clipping or shaving of hair from the operating field should be undertaken outside the operating room. A wide margin should be kept allowing for a prolongation of incisions, if necessary, and to prevent contamination from the margins. Hair may be removed by either wet (blade) or dry (clippers) shaving. Due to the epidermal damage caused, shaving (and wet shaving in particular) may lead to a tenfold increase in postoperative wound infections. For this reason, it is best to shave immediately prior to the operation.

After positioning the patient, loose hair may be removed together with organic debris. This is followed by an initial surgical site preparation with a soap containing povidone iodine or chlorhexidine. After washing, the field should be rinsed with water, saline or alcohol.

Depending on the protocol used – which may vary depending on the institute and species – this is followed by 1 to 2 washes with the products mentioned above (Figure 4). This washing should be restricted to the area of the expected incision followed by circles around this area (‘from inside to outside’ and ‘from clean to dirty’) until the used swabs (4×4’s) come away visibly clean. After the area is made dry with clean 4x4s, a final antiseptic solution (alcohol with chlorhexidine or povidone iodine after degreasing the skin with alcohol) may be applied. Once this is dry, the patient may be draped.

Figure 4. The wound area on the lower leg of a cat is cleaned prior to the operation. This should be performed as gentle as possible.

2.6.2 Preparing the surgeon

A surgeon should change into special operating clothes, which are clean, comfortable and only worn in the operating room in order to reduce environmental contaminants to a minimum. For the same reason, the surgeon should wear special operating shoes or clogs which should be kept clean and not leave the operating room (Figure 5).

Figure 5: The surgeon, nurse and sterilizing assistant should wear special and clean clothing.

During preparation of the operation, all head and facial hair should be covered with a disposable or washable cap or bonnet, as hairs are easily contaminated with environmental bacteria. If these hairs fall out during surgery, they may contaminate the surgical field. The use of surgical headwear leads to a proven reduction in wound infections. A disposable mask will protect the wound against sweat droplets and nasal discharge from the surgeon, but it does not constitute an effective bacterial filter. However, when donned correctly, they direct the airflow away from the operating wound and may thereby reduce the risk of wound infection. Although this has never been proven by clinical research, surgical specialists nevertheless see this as an important part of the ‘antiseptic attitude’. Mouth masks should be replaced after every operation in order to avoid saturation with moisture.

Once properly dressed, the surgeon should aseptically prepare the skin of his/her arms to eliminate any transient and/or resident flora. Transient flora consists of micro-organisms which have arrived by coincidence on the skin, but which do not multiply and generally die spontaneously over time. Transient flora mainly resides at the surface and can largely be eliminated mechanically (by washing). Resident flora comprises the natural bacterial population of the skin. These are mainly micrococci, in particular Staphylococcus pseudoepidermidis, corynebacteria and sometimes Staphylococcus aureus in dogs and cats. However, other pathogens may also colonize the skin. Resident flora is more deeply located and more difficult to eliminate than transient flora. Special washing protocols have been designed to decrease resident flora and limit their potential contamination of the surgery site. These protocols may vary according to country or region. In the Utrecht University Department of Clinical Science of Companion Animals, we use, for instance, the Dutch national working group Infection Prevention protocol for the cleaning and aseptical preparation of hands. Alternatively, an international hand hygiene protocol, in multiple languages, is available via (Figure 6).

Figure 6. An international hand hygiene poster in multiple languages is available via

The popularity of antibacterial soaps has decreased since it was revealed that the reduction of transient bacteria, they bring about is equivalent to that of ordinary soap, and considerably less than the rubbing-in of alcohol-based solutions. Most commercial cleansers of the surgeon’s hands are a combination of alcohol and antiseptics such as chlorhexidine. The addition of chlorhexidine does little to contribute to the initial rapid bactericidal effect obtained by alcohol alone, but it delays the regrowth of residential flora as a result of its residual activity.  This residual activity ensures that the number of bacteria inside the surgeon’s glove remains low for several hours and is vital in view of the frequent occurrence of mini perforations in operating gloves. In surgery, alcohol antisepsis with residual action has largely replaced lengthy scrubbing with water and (disinfecting) soap.

The Dutch working group Infection Prevention has drawn up the following guidelines for preoperative aseptical preparation of hands (2012):

  • wash hands with water and soap; use a soft brush for the nails and knuckles to remove visible dirt
  • dry well with clean paper towels
  • rub hands and arms with antiseptic solution according to manufacturer’s guidelines
    • for instance, 5-10 ml chlorhexidine 0.5% in ethanol 70% until the skin is dry, followed by another rub with 5-10 ml chlorhexidine 0.5% in ethanol 70% until the skin is dry OR
    • rub hands and arms with 80% ethanol (Sterilium®) solution for 90 seconds, starting with the fingers and spreading to the entire hand and onto forearms, ensuring hands remain moist for the entire application time.               
  • Don operating clothes (disposable or not) and gloves

For every subsequent operation during the same session, a simple disinfection is sufficient (unless the surgeon has left the OR between operations).

2.6.3 Operating gowns

Operating gowns should always be used in the case of invasive surgical procedures. They should be impermeable to water and bacteria and should be fire resistant (in case laser or electrocoagulation techniques are used). Both cotton, reusable gowns (cheaper, but they need to be washed and stored) or disposable gowns (more expensive and wasteful, but less risk of contaminating the operating environment caused by fluid penetration) are available. Most studies show that the use of disposable gowns decreases the contamination rate and, to some extent, the surgical infection rate as well. The surgeon takes the gown from its sterile wrapping and opens it in such a way that the arms can be put into the sleeves without exteriorizing the hands (the gown is opened at the back; the front is in one piece). The gown can then be tied or closed at the surgeon’s back by an assistant, who should take care not to touch any part of the gown that needs to remain sterile. Once the surgeon has gloved, he may hand the disposable gown’s sterile, detachable, cardboard tab to an assistant, who will help to fasten the gown. The tab is found in the front of the gown and is attached to a fastening strap. Once the assistant has a hold of the tab, the surgeon may spin around until the gown is wrapped around his body and can take the fastening strap from the assistant. It is important that the assistant retains the detachable cardboard tab, as it has been contaminated during the exercise. The surgeon can now tie the fastening strap to the strap found on the left-hand side of the gown (Figure 7).

Figure 7: Surgeon wearing a sterile disposable operating gown

2.6.4 Gloves

The use of gloves during surgical procedures is always recommended. This not only results in a reduction in bacterial contamination of the operating field by the continuously present residential flora on the surgeon’s hands, but also prevents the development of allergies and contact dermatitis against blood and blood protein, which may arise due to permanent exposure.

Most gloves are made of latex, intended for single use and available in various sizes. Wearing the correct size is of great importance for the surgeon. Oversized gloves may complicate the handling of instruments and suture material; whilst undersized gloves may lead to a decreased sensitivity of the fingers.

Gloves usually contain magnesium silicate powder to facilitate their donning. Once donned, the outside of the gloves should therefore be rinsed briefly before they come into contact with the patient to prevent any possible tissue reactions against this substance. In some cases, the surgeon may develop a skin reaction to the latex or the powder. Hypoallergenic gloves made of non-latex materials such as vinyl, nitrile rubber or neoprene and powder-free medical gloves are also available.

Gloves should be inspected before and at regular intervals during the surgical procedure for perforations and other defects. Studies have shown that 2.7% of all gloves leak water, and up to 13% have undiscovered perforations after the procedure. In some (orthopedic) procedures, a double glove technique is used.

Gloves may be put on using a closed or an open technique. Closed gloving is preferred, as this prevents accidental contact between the surgeon’s fingers and skin and the outside of the gloves. With experience, it is possible to put on gloves using this method rapidly and safely, in particular when using disposable operating gowns. It is important to ensure that the cuff of the gloves reaches well over the cuff of the operating gown.

Closed gloving procedure (Figure 8)

8.1 The gloves are positioned with the cuffs pointing towards the surgeon.
8.2 The right-hand glove is picked up by the folded cuff with the ‘closed’ left hand (still inside the sleeve of the operating gown).
8.3 The right-hand glove is placed over the right hand, with the thumb of the glove on the thumb of the ‘closed’ right hand and the glove fingers pointing towards the elbow.
8.4 The edge of the inside glove cuff (closest to the right hand) is grasped at its base by the ‘closed’ right hand. The outer base of the cuff (closest to the left hand) is taken by the ‘closed’ left hand…
8.5 …and pulled over the back of the right hand.
8.6 With the cuff held in place by the left hand, the right-hand fingers are put into the glove.
8.7 The inside (uppermost) free cuff edge is taken by the ‘closed’ left hand…
8.8 …and is pulled over the right wrist.
8.9 The fingers are positioned into the glove with help of the ‘closed’ left hand.
8.10 The cuff is pulled downward by the ‘closed’ left hand.
8.11 The folded cuff of the left-hand glove is picked up by the right hand.
8.12 The left-hand glove is placed on the ‘closed’ left hand, with the glove thumb over the left-hand thumb and the other glove fingers pointing towards the elbow.
8.13 The inside cuff is grasped at its base by the ‘closed’ left hand. The outer cuff base is taken by the right hand…
8.14 …and is pulled over the back of the left hand.
8.15 The inside (uppermost) free cuff edge is then taken by the right hand…
8.16 …and is pulled upwards over the wrist.
8.17 With the glove held in place by the right hand, the fingers of the left hand are slid into the glove.

Open gloving procedure (Figure 9)

9.1 The gloves are positioned with the cuffs pointing towards the surgeon.
9.2 The left hand picks up the right-hand glove by the folded cuff base.
9.3 The fingers of the right hand are slipped into the glove. Take care to insert the thumb on the correct side and not to touch the sterile parts of the glove (outside of the glove).
9.4 Using the left hand, the folded cuff base of the glove is pulled over the cuff of the operating gown, taking care not to touch the gown with the left hand.
9.5 The cuff is released by the left hand.
9.6 The index and middle finger of the right hand are slid under the free cuff edge of the left-hand glove.
9.7 The left-hand glove is picked up by carefully slipping 2 fingers into the folded cuff…
9.8 …and the left hand carefully slipped into the cuff.
9.9 With a smooth movement, the right hand pulls the free cuff edge over the cuff of the operating gown whilst the left hand is further inserted into the glove.
9.10 With a smooth movement, the right hand pulls the free cuff edge over the cuff of the operating gown whilst the left hand is further inserted into the glove.
9.11 The index and middle finger of the left hand are slid under the free cuff edge of the right-hand glove.
9.12 With a smooth movement, the left hand pulls the free cuff edge over the sleeve of the operating gown, whilst the right hand is further inserted into the glove.
9.13 The end result.

2.6.5 Draping the sterile field

For the draping of the sterile field, both cotton and disposable drapes are available. Disposable adhesive drapes are preferable as they are easy to put on and stay in place without the need for towel clamps, which cause micro-perforations of the skin. Furthermore, contamination, such as blood and fecal material, may be difficult to remove from cotton drapes. In the standing animal, draping is more complicated and draping with laces or adhesives are preferred.

The drapes should be positioned in such a way that a breach in asepsis is avoided. All visible parts of the patient and the operating table should be covered. The operating field itself should remain exposed, with a small margin on all sides to allow prolongation of the incision if necessary, and the placement of active or passive wound drains.

By placing the drapes, a surgical field is created which is only considered sterile at the level of the operating wound and above (but not beneath, i.e. the hanging sides of the drapes, and the front of the surgeon’s gown, from below the shoulders to the waist and including the arms. The gloved hands of the surgeon and the operating team should therefore remain within this area at all times!

2.7 References

  1. Auer JA, Stick JA. (2012) Equine Surgery. 4th edition. St Louis, Missouri: Elsevier Saunders. Chapters 9 and 10.
  2. Johnston SA. & Tobias KM (2018) Veterinary Surgery Small Animal. St Louis, Missouri: Elsevier Saunders. Chapters 11 and 13.
  3. Fossum TW. (2018) Small Animal Surgery. 5th edition. St Louis, Missouri: Elsevier Saunders. Chapters 1, 2, 5 and 6.
  4. Werkgroep Infectiepreventie. (2013) Ziekenhuizen preoperatieve handdesinfectie. Richtlijn NEN-EN 12791

Recommended reading

  1. Lemarie RJ, Hosgood G. (1995) Antiseptics and disinfectants in small animal practice.  Compendium of Continuing Education for the Practicing Veterinarian, 17(11):1339
  2. Allen G, Josephson A. (1995) Meeting infection control standards in the operating room. AORN Journal, 62:595
  3. Osuna DJ, DeYoung DJ, Walker RL. (1990) Comparison of three skin preparation techniques in the dog. Part 1: Experimental trial. Veterinary Surgery, 19(1):14-9
  4. Osuna DJ, DeYoung DJ, Walker RL (1990) Comparison of three skin preparation techniques in the dog. Part 2: Clinical trial in 100 dogs. Veterinary Surgery, 19(1):20-3
  5. Garibaldi R, Maglio S, Lerer T, et al. (1986) Comparison of nonwoven and woven gown and drape fabric to prevent intraoperative wound contamination and postoperative infection. American Journal of Surgery, 152(5):505-9
  6. Kac G, Masmejean E, Gueneret M, et al. (2009) Bactericidal efficacy of a 1.5 min surgical hand-rubbing protocol under in-use conditions. Journal of Hospital Infection, 72(2):135-9

CV’s Authors

Dr. Jos Ensink, DVM, Ph.D., Diplomate ECVS, graduated from the Utrecht University Faculty of Veterinary Medicine, The Netherlands, in 1987. In the same year, she started her internship, followed by her residency at the Dept of General and Large Animal Surgery of Utrecht University, later Department of Equine Sciences. In 1995 she got her Ph.D. with the thesis entitled “Pharmacokinetics and clinical aspects of oral broad-spectrum penicillins in the horse.” Since 1994 she is a specialist in Equine Surgery of the RVNA, and in 1997 she became a Diplomate of the ECVS (Large Animal Surgery). Her primary clinical and research interests are soft tissue surgery, oncology, and ophthalmology.

Dr. F. Herman Jonker, DVM, Ph.D., Diplomate ECAR, ECBHM (np), graduated from the Utrecht University Faculty of Veterinary Medicine, The Netherlands, in 1981. In 1982 he started as an intern at the former Dept of General and Large Animal Surgery of Utrecht University. In 1983 he switched to the Dept of Obstetrics, Gynecology and AI, now the Department of Farm Animal Health. In 1993 he got his Ph.D. with the thesis entitled “Cardiotocographic Monitoring of the Bovine Fetus.” Since 2000 he became a Diplomate of the ECAR (European College of Animal Reproduction). His main clinical and research interests are obstetrics, perinatology, and reproductive surgery.

Chapter 3 Surgical instruments

Jolle Kirpensteijn, DVM, PhD, Diplomate ACVS & ECVS (Small Animal)

Gert ter Haar, DVM, PhD, MRCVS, Diplomate ECVS (Small Animal)

with contributions from

Lars FH Theyse, DVM, PhD, Diplomate ECVS (Small Animal)

Based on the previous edition of and with contributions from

Wim Klein, DVM, PhD, Dipl ECVS (Equine)

3.1       Introduction

3.2       The surgical knife

3.3       Scissors

3.4       Forceps

3.5       Needle holders

3.6       Tissue forceps and bone-holding forceps

3.7       Vascular or artery forceps (hemostats)

3.8       Retractors

3.9       Emasculators

3.10     Towel clamps

3.11     Spay hooks

3.12     Periosteal elevators and bone-cutting instruments

3.13     Suction tips

3.14     Miscellaneous instruments

3.15     Cleaning your instruments

3.1 Introduction

Surgical instruments are made of stainless steel. Stainless steel has a high, but not complete, resistance against corrosion. Carbon inlays are sometimes used for parts needing extra strength and which are prone to excessive wear and tear by frequent use (such as needle holders). Fine instruments are made of titanium alloys and require extra care when cleaning and sterilizing. Gold-colored handles indicate instruments of superior quality.

3.2 The surgical knife

The surgical knife used to cut tissues is referred to as a scalpel and is usually made up of a Bard-Parker-type handle (Figure 1a) with a disposable blade. The most commonly used disposable blades are numbers 10, 11, 12, 15 and 22. Every type of blade has a special shape and purpose (Figure 1b). Disposable blades guarantee a sharp knife at all times and create less trauma than non-disposable ones and are therefore usually recommended. However, disposable blades should not be used in joints or for deep cuts in solid connective tissue since there is an increased risk of breakage and loss of part of a blade in these situations. For these special indications, other scalpels are available.

In otorhinolaryngologic, reconstructive, ophthalmic and some orthopedic surgeries, very small, disposable, so-called ‘beaver’ blades are used. These blades are used for delicate incisions; for instance, a 6400-rounded blade can be used during partial meniscectomies. Several blade types are available, and they require a specific beaver blade holder (Figure 1c).

Figure 1C. Beaver blade and holder

The ‘pencil grip’ is used for short or sharply curved incisions. In this grip, the muscles of the hand and the upper arm are used to direct the scalpel, allowing small and accurate movements. As the scalpel is held almost vertical and mainly uses the tip of the blade, it is only in partial contact with the wound edges. This facilitates the making of curves and improves the accuracy of the incision (Figure 2).

Figure 2. Pencil grip

The ‘fingertip grip’ or ‘palm grip’ is used for long, slightly curved or straight incisions. The scalpel is held more horizontally so that the blade is in contact with the tissue over a longer distance (using the belly of the blade; Figure 3). This grip stabilizes the scalpel and reduces the effect of the variable blade pressure on the depth of the incision. In this grip, the scalpel is predominantly guided by the arm muscles. There is less radial deviation, which makes the grip less tense.

Figure 3 .The palm grip

The incision should be made with a fluid movement without removing the blade from the wound. This avoids the ragged edge of several subsequent incisions. When cutting through the skin, the free hand may pull the skin tight for better control of the scalpel pressure and hence the depth of the incision (Figure 4).

Figure 4. The pencil grip used for an incision

When making a stab incision, the scalpel is placed perpendicular to the tissue and is pushed downwards until the resistance of the upper layer is overcome and the scalpel penetrates into the tissue. As this often occurs abruptly, stab incisions are only carried out if there is sufficient room beneath the surface for the scalpel to enter without causing damage (Figure 5a and 5b). Examples include the opening of liquid- or gas-filled cavities (abscess, hygroma) or organs (urinary bladder, stomach).

Figure 5A. A stab incision
Figure 5B. The stab incision continued

Care should be taken when fitting or removing blades in order to avoid iatrogenic trauma to the patient, assistant or veterinary surgeon (Figure 6). The blade can be attached to the handle using either a special instrument or a needle holder. The blade should be grasped with the cutting edge facing away from the operator, and the central ridge of the handle pushed into the central blade socket. The authors prefer this technique over using fingers to grasp the blade to avoid iatrogenic trauma. To remove the blade, the end should be lifted with a needle holder and the handle pulled away from the blade.

Figure 6. The correct way to put a blade on a blade holder. The blade can be attached to the handle using either a special instrument or a needle holder. The blade should be grasped with the cutting edge facing away from the operator, and the central ridge of the handle pushed into the central blade socket.

3.3 Scissors

Scissors consist of the following parts:

•           blades

•           joint

•           legs

•           eyes

Scissors are held in the index-ring finger-thumb grip or three-point grip, where the fingers form a triangle with a wide base, resulting in a stable grip and good guidance control.

There are two types of scissors: dissecting scissors and ligature scissors. Dissecting scissors have smooth, polished blades with rounded tips for minimal tissue trauma. They are used for both cutting and blunt dissection. Cutting is considered as sharp trauma, dissection as blunt trauma. Sharp trauma damages less tissue than blunt trauma, but the damage itself is usually more severe and more difficult to repair than that following blunt trauma. Blunt dissection is primarily used if the area where the tissue needs to be parted is not clearly visible and there is a danger of accidentally transecting blood vessels or nerves. Dissecting scissors may be straight or curved. Straight scissors are used only if cutting in straight lines is necessary (for example, the opening of the abdomen along the midline). Curved scissors are used if cutting in a straight line is not absolutely necessary or if both cutting and blunt dissection are required.

The precision of cutting is largely determined by the amount of tissue positioned between the blades of the scissors. In order to cut with accuracy, the scissors should not be opened too wide; cutting small amounts of tissue with the tip of the scissors is easier to guide than the cutting of large amounts with the whole ‘bite’. When curved scissors are used for straight cutting, they should be held in such a way that the tip of the blades point straight ahead. When cutting with a ‘forehand’ hold, the convex side is best placed on the outside; in this way, the wrist does not need to be bent as much as the other way around (Figure 7a and 7b). The same applies when cutting in ‘backhand’ position. However, when changing from ‘forehand’ to ‘backhand’, the scissors should be rotated 180° on their long axis. In such cases, it is easier to hold the scissors with the convex side towards the operator in ‘backhand’ position; however, it may even be easier to avoid cutting ‘backhand’ altogether. Right-handed surgeons may achieve this by starting the incision at the extreme right-hand side; in this way, cutting is only necessary from right to left. Left-handed surgeons should start on the left-hand side.

Figure 7A. When cutting with a ‘forehand’ hold, the convex side is best placed on the outside; in this way, the wrist does not need to be bent as much as the other way around
Figure 7B. Scissors are held in the index-ring finger-thumb grip or three-point grip, where the fingers form a triangle with a wide base, resulting in a stable grip and good guidance control.

Slide cutting is a special form of cutting where the scissor blades are not alternately opened and closed but are kept at a fixed angle. The tissue is parted by pushing the scissors forwards without moving the blades; in doing so, the scissors act as a double knife. This method of cutting is used in particular for incising loose tissue layers, such as the peritoneum, pleura and pericardia.

Blunt dissection is obtained by inserting the scissors in closed position and opening them once inside the tissue to separate tissue layers. The round edges of the blades ensure that damage to delicate structures is avoided.

The most commonly used dissecting scissors are Mayo scissors (wide model; Figure 8a and 8b) and Metzenbaum scissors (narrow model; Figure 8c). These scissors should not be used for cutting suture material as this may make them blunt. Ligature scissors should be used to cut suture material (Figure 8d). Lister bandage scissors can be used to cut bandage material and aid in applying and removing bandages (Figure 8e).

Figure 8A and 8B. The most commonly used dissecting scissors are Mayo scissors. Figure 8C. Metzenbaum scissors. Figure 8D Ligature scissors should be used to cut suture material. Figure 8E. Lister bandage scissors can be used to cut bandage material and aid in applying and removing bandages.

3.4 Forceps

Forceps are surgical instruments used for delicate tissue handling, not fixation. Generally, two types of tissue handling forceps are distinguished: operating and dissecting forceps. Operating forceps are toothed (Adson, Adson-Brown), while dissecting forceps are not. The use of dissecting forceps has greatly diminished since the introduction of so-called atraumatic surgical forceps (Figures 9a and b). These forceps have a special profile which allow the fixing of the tissue with minimal pressure. Atraumatic forceps were originally designed for cardiac and vascular surgery and carry the names of famous (US) heart surgeons: DeBakey and Cooley. These forceps are now also used in gastro-intestinal surgery and urology, and increasingly for finer tasks in general surgery.

Figure 9 A. Debakey atraumatic forceps

Figure 9B. Surgical (operating) forceps. Note the difference in the teeth.

Forceps are held so that one leg is placed as a prolongation of the index finger, the other as that of the thumb (pencil grip) (Figure 9c).

Figure 9C. A Debakey forceps in a pencil grip

This allows the instrument to be guided with precision. If the forceps are held like the handle of a saucepan, however, deeper parts may only be reached by excessive bending of the wrist, which severely limits their manipulation (Figure 9d).

Figure 9D. Incorrect placement of forceps in the surgeon’s hand

If the forceps are used intermittently, for example when placing interrupted sutures, they can be held in the palm of the hand (Figures 9e and 9f).

Figure 9E. If the forceps is used intermittently, it can be placed in the palm of the hand
Figure 9F. If the forceps is used intermittently, it can be placed in the palm of the hand

3.5 Needle holders

Needle holders are delicate instruments that aid the passage of a needle with suture material through tissues. The most commonly used needle holders in veterinary practice are the Mathieu (especially in large animal surgery) and the Mayo-Hegar needle holders (small animals) (Figure 10a and 10b). The main difference between the two types is the force applied on the needle while opening and closing the ratchet.

Figure 10A. Mayo-Hegar needle holders
Figure 10B. Mathieu needle holders

The Mathieu needle holder has a graded lock, which should be pushed in all the way in order to release it again (Figures 11).

Figure 11. The Mathieu needle holder has a graded lock, which should be pushed in all the way in order to release it again

This results in maximal pressure on the needle every time the needle holder is opened, which may lead to a flattening of the curve in fine, curved needles. The larger Mathieu needle holder is therefore less suitable for fine needles and suture material.

The Mayo-Hegar needle holder is most commonly used in general soft tissue surgery. This needle holder can be opened in any position and is much more ‘needle friendly’ but is not very suitable for large needles. The Mayo-Hegar is therefore less appropriate for heavy-duty surgery.

Mathieu needle holders are held in the palm of the hand. The index finger may be positioned against the joint of the instrument to fine-tune the manipulation. The needle holder is opened by pressure on its legs until the toothed lock springs open. Mayo-Hegar needle holders are held in the thumb-ring finger grip (three-point grip) or in the palm grip. With the three-point grip, the fingers are placed as follows:

  • the thumb and ring finger in the eyes of the needle holder
  • the index finger extended against the joint
  • the middle finger bent over the lower leg, just above the eye (see Figure 12).
Figure 12. Three-point grip of a Mayo-Hegar needle holder

In this way, the hand forms a triangle with the largest possible base for improved stability. The position of the index and the middle finger ensure good dexterity.

The Mayo-Hegar needle holder is opened by pushing the eyes in opposite directions; the lock is released automatically, independent of the degree of closure. Left-handed surgeons should only use a left-handed Mayo-Hegar because of the lock releasing mechanism. When using the palm grip, the needle holder is held in the palm of the hand; no fingers are put through the eyes. The needle holder is opened and closed by pressure from the palm and surrounding fingers (Figure 13).

Figure 13. Closing and opening of a Mayo-Hegar needle holder using a palm grip

The Olson-Hegar needle holder is a combination of a needle holder and scissors. This combination allows a reduction in operating time but increases the risk of accidentally cutting a suture. Special needle holders are designed for ophthalmic surgery (See Chapter 15).

3.6 Tissue forceps and bone-holding forceps

Soft tissue forceps and bone-holding forceps are used to fixate and manipulate soft tissues and bone, respectively. Soft tissue forceps exist in two versions:

  • traumatic tissue forceps, e.g. Allis forceps, (Figure 14a)
Figure 14A. Allis forceps
  • atraumatic tissue forceps, e.g. Babcock or Doyen forceps, (Figure 14b)
Figure 14B. Doyen forceps

Atraumatic tissue forceps are used to avoid damage to delicate tissues. Babcock forceps for example, are used in cardiac and gastric surgery, while Doyen tissue forceps are mainly used in intestinal surgery. Both straight and curved versions are available. The use of traumatic forceps should be limited to tissues that are to be removed from the body. Bone-holding forceps are generally used during orthopedic procedures (fracture treatment) to realign and reduce bone segments (such as Kern bone holding forceps, Figure 15) or to temporarily stabilize fracture segments during osteosynthesis (for example, reduction forceps with speed lock, Figure 16).

Figure 15. Kern bone holding forceps
Figure 16. Bone reduction forceps with speedlock

3.7 Vascular or arterial forceps (hemostats)

The most commonly used vascular or arterial forceps are the Halsted mosquito forceps, the Kocher forceps (with pointed tips for a better grip), Pean artery forceps (wide tip) and the Kelly forceps (no sharp tips) (Figure 17a-c).

Figure 17A. Straight Halsted Mosquito forceps
Figure 17B. Curved Halsted Mosquito forceps
Figure 17C. Pean artery forceps

The nomenclature for the Pean is confusing because it is sometimes used to describe a longer version of a mosquito. These forceps are also known as Rochester Pean artery forceps. More specialized vascular forceps are available for cardiovascular surgery, such as the Mixter forceps (Figure 17d)

Figure 17D. Mixter vascular forceps

Mosquito forceps are mainly used for capillary bleeding or to aid in small vessel ligation; the others for larger vessels and vascular stumps. Artery forceps usually exist in straight and curved shapes and are also held in the three-point grip (Figure 17e).

Figure 17E. A curved Halsted Mosquito forceps in a three-point grip

3.8 Retractors

Tissue retractors will enhance access to a surgical site and improve visibility. They can be divided into finger-held retractors, hand-held retractors and self-retaining retractors.  The finger held retractors (e.g. the Senn retractor, Figure 18a) are the most straightforward, and are available in sharp and blunt versions.

Figure 18A. The Senn retractor

The Army-Navy (Figure 18b), Hohmann (Figure 18c) and flexible retractors are examples of handheld retractors. Hohmann retractors are commonly used in stifle surgery, for example, to distract the joint.

Figure 18B. The Army-Navy retractor
Figure 18C. A Hohmann retractor

Commonly used self-retaining retractors include:

  • Weitlaner retractors – with blunt tips for use in small cavities (Figure 19a)
Figure 19A. Weitlaner retractor
  • Gelpi retractors – with sharp tips for use in small cavities
Figure 19B. Gelpi self-retaining forceps
  • Collins retractors – for use in the caudal abdomen in the dog (Figure 19c)

Figure 19C. Collins retractor
  • Finochietto retractors – for use in the thorax (Figure 19d)
Figure 19D. Finochietto retractor
  • Balfour retractors – for use in the abdomen (Figure 19e)
Figure 19E Balfour abdominal retractor

3.9 Emasculators

The most commonly used crushing clamps for the castration of horses are Sand emasculators. They only crush and do not have a cutting edge (Figure 20). In piglets, the Hausmann emasculator, which has both a cutting and crushing blade, may be used. In cattle, Burdizzo emasculators are used for closed castration.

Figure 20 Sand emasculator

Elastrators are used to place a strong rubber band over the scrotum, used in certain countries for the castration of lambs. In the Netherlands, it is also used for tail amputations in lambs. Elastrators are forbidden by many countries (including the Netherlands) to be used in dogs and horses.

3.10 Towel clamps

Towel clamps are used to attach the drapes to each other (non-perforating) or to the skin (perforating). The most commonly used non-perforating towel clamps are Pean artery forceps (Figure 17c). Backhaus perforating towel clamps are mainly used in large animal surgery (Figure 21a and 21b), and the finer Jones towel clamps predominantly in small animals (Figure 21c).

Figure 21A and B. Backhaus towel clamp (large and small)
Figure 21C. Jones towel clamp

3.11 Spay hooks

The use of the Snook spay hook facilitates the grasping of the uterine horn during the neutering of the bitch or cat (Figure 22).

Figure 22. The spay hook

3.12 Periosteal elevators and bone-cutting instruments

Periosteal elevators aid in reflecting muscle, periosteum and other soft tissues from bone. They are available in various shapes and sizes (Figure 23).

Figure 23. Periosteal elevator

Bone-cutting instruments include osteotomes, saws, curettes, rongeurs and trephines. Army pattern osteotomes and Lambotte osteotomes, used with a mallet or hammer, are most commonly used in orthopedic surgery and neurosurgery (Figure 24a and 24b).

Figure 24A. Army pattern osteotome
Figure 24B. Lambotte osteotome
Figure 24C. Mallet

Most osteotomes come in a large range of sizes. Curettes have a cupped end that allows for the removal of bone or soft tissue from restricted sites (Figure 25a).

Figure 25A. Curette

For example, during bulla osteotomy or for cancellous bone harvesting (Volkmann and Spratt bone curette, Figure 25b).

Figure 25B. Volkmann and Spratt bone curette

Rongeurs are forceps with cupped jaws and blunted or tapered tips and are used to remove pieces of bone during neurosurgical, otologic and orthopedic procedures (e.g. a Ruskin double action rongeur, Figure 26).

Figure 26. Ruskin double action rongeur

Trephines, such as the Michel trephine, have a central stylet for removing bone from the shaft and are used to obtain samples of bone for biopsy (Figure 27).

Figure 27. Michelle trephine

3.13 Suction tips

Excessive fluids or blood may be removed by suction. The best-known suction tips are the Yankauer and Poole suction tips (Figure 28a and 28b), which are principally used in body cavities (abdomen, thorax).

Figure 28A. Yankauer suction tube
Figure 28B. Poole suction tube

More delicate suction tubes, such as the Ferguson Frazier suction tubes (available in several sizes, Figure 28c), can be used for removal of blood and/or irrigation in smaller spaces such as joints and the middle ear cavity, for example.

Figure 28C. Ferguson Frazier suction tube

3.14 Miscellaneous instruments.

Many other instruments have been developed to aid the surgeon in handling and manipulating tissues or to aid in osteosynthesis. For example, a Jacob’s hand chuck and key are one method of placing pins or wires in bone (Figure 29).

Figure 29. Jacob’s hand chuck

Wire or pin cutters (Figure 30) and instruments to stabilize and bend bone wires and pins, such as parallel action pliers, are frequently used during orthopedic procedures (Figure 31).

Figure 30. Wire cutter
Figure 31. Parallel action pliers

Instruments used for exploring wounds, cavities and pockets are called probes (Figure 32).

Figure 32. Eye probe

3.15 Cleaning your instruments

Instruments need careful cleaning, lubrication and dry storage after use. This prolongs the life expectancy of the instrument and protects against instrument failure and corrosion. The best way to guarantee a long instrument life is to use a standardized protocol for cleaning in which longer-term maintenance should have a part (Table 1). Long-term maintenance can be discussed with your local supplier.

Table 1. Abbreviated maintenance plan for surgical instruments

  1. Dismantle all instruments if possible
  2. Rinse and clean all instruments with clean water and a detergent
  3. Use soft brushes to remove adherent materials
  4. Use an ultrasonic cleaning apparatus to further remove debris
  5. Use an industry-style washing machine to clean the instruments, if available
  6. All instruments need to be carefully checked for wear and tear
  7. Jointed instruments should be treated regularly with adequate lubrication solutions
  8. Dry instruments and pack for autoclaving
  9. Autoclave instruments and store appropriately

Please note that there are many instruments made of other materials such as plastic and rubber. Each material will require a separate protocol for optimal cleaning. All protocols must be readily available for all personnel.

3.16 References

Bacon, N.J. (2012). Surgical instruments – Types and use. In: Baines, S., Lipscomb, V. and Hutchinson, T. (eds), BSAVA Manual of Canine and Feline Surgical Principles. (BSAVA), pp. 28-38.

Boothe, H. (2018). Instrumentation. In: Johnston, S.A. & Tobias, K.M. (eds), Veterinary Surgery: Small Animal (St Louis: Elsevier-Saunders), pp. 165-76.

Lapish, J. (2012). Surgical instruments materials, manufacture and care. In: Baines, S., Lipscomb, V. and Hutchinson, T. (eds), BSAVA Manual of Canine and Feline Surgical Principles. (BSAVA), pp. 22-27.

CV’s authors

Dr. Lars Theyse graduated from the Faculty of Veterinary Medicine, Utrecht University, the Netherlands, in 1989. After his graduation, he served in the cavalry of the Royal Netherlands Army. Immediately after, he started an internship and consecutive ECVS residency at Utrecht University. He was appointed lecturer and at a later stage associate-professor in Orthopedics, Neurosurgery, and Craniofacial & Oral Surgery. In 2006 he completed his Ph.D. in Clinical and Experimental Studies of Osteogenesis in Dogs. He received his Senior Qualification in University Teaching at Utrecht University in 2011. From 2014 to 2020, he was a member and chair of the ECVS Examination Committee. In 2015 he was appointed Professor in Small Animal Orthopedic Surgery at the Royal Veterinary College London, University of London, United Kingdom. Unfortunately, Brexit forced him to leave the RVC at the end of 2016. After a short stay in private specialist practice, he was appointed as Professor in Small Animal Surgery at Leipzig University, Germany, where he works. His clinical and research interests are distraction osteogenesis, bone, joint regeneration, fracture treatment, traumatology, and neurosurgery. Lars is a keen sportsman, including hockey, sailing, and skiing.

Chapter 4 Electro-, cryo-, laser and endoscopic surgery

Bart Van Goethem, DVM, Dipl ECVS (small animal)

with contributions from

Nico Schoemaker, DVM, PhD, Dip ECZM (small mammal & avian), Dipl. ABVP (avian)

Jos Ensink, DVM, PhD, Dipl. ECVS (large animal)

4.1 Electrosurgery

            4.1.1 Introduction

            4.1.2 Electrocautery




            4.1.3 Monopolar electrocoagulation and electrosurgery




            4.1.4 Bipolar electrocoagulation and electrosurgery




            4.1.5 Radio wave radiosurgery




            4.1.6 Vessel sealing




4.2 Cryosurgery

            4.2.1 Introduction

            4.2.2 Technique

            4.2.3 Applications

            4.2.4 Disadvantages

4.3 Laser Surgery

            4.3.1 Introduction

            4.3.2 Technique

            4.3.3 Applications

            4.3.4 Disadvantages

4.4. Endoscopic Surgery

            4.4.1 Introduction

            4.4.2 Technique

            4.4.3 Applications

            4.4.4 Disadvantages

4.5 References

4.1 Electrosurgery

4.1.1 Introduction

In electrosurgery or diathermy, heat is generated in the patient’s tissue due to an electric current, with the aim of using this heat for hemostasis or for making incisions. Electric current is the flow of free charge carriers – electrons and ions – from a positive electrode (the source) to a negative electrode or ground. Electric currents are defined by polarity and frequency. Current of a constant polarity is referred to as direct current (DC) whereas a current of alternating polarity is referred to as alternating current (AC). Its frequency is measured in cycles per second or hertz (Hz). The effect of an electric current on tissue mainly depends on its power (W; watt), which is determined by (and the product of) its voltage (V; volt) and current (A; amperes): W = V x A. Current flow through the tissues is described by Ohm’s Law, in which voltage (V) is the product of current (A) and resistance (Ω; ohm).

Electrosurgery requires an electrosurgical generator that changes the standard 50 or 60 Hz, low frequency electrical current into a useable high frequency 200 kHz to 5 MHz current. Since the neuromuscular system becomes refractory to electrical stimulation beyond a frequency of 100 kHz, there is minimal stimulation when using these high frequencies. The spectrum mentioned falls within the electromagnetic spectrum of low radiofrequency bands (AM broadcast signals 550-1550 kHz). Some units go as high as 3-4 megahertz (MHz) and occur in the range between AM and FM radio broadcasting. These are referred to as radio wave radiosurgery units (Figure 1).

Figure 1. Most electrosurgical units operate in the low radiofrequency bandwidth (AM broadcast). Radio wave radio surgical units operate in the high radiofrequency bandwidth (FM broadcast).

When heat is applied to a biological system, the effect is temperature-related and also dependent on application time. Between 38-60°C, tissues will warm and weld without obvious visual signs. At 60-65°C irreversible damage resulting from coagulation necrosis and protein denaturation is visible as blanching. At 65-90°C protein denaturation resulting in white/greyish discoloration occurs. At 90-100°C tissues dry and show puckering. Above 100°C solid tissue vaporization results in steam and smoke, and temperatures of 350-450°C result in immediate carbonization and char formation.

The use of electrosurgical equipment has some inherent risks. Most operating room fires are caused by the use of electrosurgical equipment. Regular checks of insulation and grounding pads should therefore be performed. Smoke generated by these devices contains many carcinogenic compounds. A smoke evacuation system is therefore highly recommended.

4.1.2 Electrocautery Technique

Electrocautery is sometimes erroneously used as a synonym for electrosurgery. However, in the former technique no electric current passes through the tissues or the patient. Instead, direct current is applied to a wire, connecting positive and negative poles of electricity, resulting in the wire becoming hot. When the probe, heated to a glowing temperature, is brought into contact with tissue, it will cauterize tissue directly. A distinction is made between low temperature (400-700°C) and high temperature (800-1200°C) electrocautery.

The direct current in penlight-type devices (Figure 2) comes from dry cells. These are technically simple and therefore economical devices. They are mainly intended for short, non-sterile surgical procedures. A sterile plastic sheath and adjustable sterile tips are available to allow their use in procedures where a sterile field is necessary.

Figure 2. A battery-powered instrument for electrocautery during non-sterile surgical procedures (Bovie Medical Corporation, Clearwater, USA) Applications

Companion animal

Distichiasis (hairs abnormally implanted on the eyelids) can be treated using a fine-tipped electrocauter introduced through the hair follicle opening and subsequent direct coagulation of the follicle.

Large and production animal

Dehorning or disbudding is the process of removing or stopping the growth of the horns of livestock (cattle, sheep, and goats). Electrocautery devices can be used to destroy the growth ring of the horn in young animals to prevent regrowth.

Exotic animals

No specific indications. Disadvantages

The heated metal instrument often welds to the charred tissue, resulting in possible char dislodgment and return of hemorrhage when the instrument is retracted.

4.1.3 Monopolar electrocoagulation and electrosurgery Technique

Monopolar electrosurgical systems consist of a generator box, an electrosurgical pen, and a return electrode. The electrosurgical generator will send concentrated electrical energy from the active electrode (electrosurgical pen) through the patient’s body to the dispersive electrode (patient return pad) and finally back to the generator (Figure 3).

Electrical current flows from the tip of the electrosurgical pen, where the charge is carried by electrons, to biological tissues where conduction is primarily due to the conductivity of the interstitial fluids, and thus predominantly ionic. Transition between the electronic and ionic conduction will be characterized by increased resistance (function of blood supply and tissue composition) and is referred to as impedance. The impedance of the tissues converts electrical energy into thermal energy (heat), which causes an increase in tissue temperature. The amount of thermal energy and the time rate of delivery will determine the heat and resultant tissue effects.

Figure 3. Electric current flows from the electrosurgical generator through the active electrode into the patient. The dispersed current is collected by the patient return pad and sent back to the generator.

The waveform sent by the generator can be adapted for desired effect. A cut waveform is continuous and of lower voltage (Figure 4). The cutting waveform produces an intense localized effect on the tissues, creating high tissue temperatures, vaporization, and subsequent cutting with little hemostasis. The generator power setting is between 50-80 W. The coagulating waveform is the highest voltage waveform but is interrupted. The higher voltage drives the electrical charge deeper into tissues. The significant delay in its on-off cycle allows for cooling between energy bursts. The generator power setting is in the range of 30-50 W. Variations in blended waveforms allow the tailoring of tissue effect towards cutting or coagulation.

Figure 4. Electrosurgical generators produce waveforms optimal for cutting (continuous low voltage), coagulation (interrupted high voltage) and blended forms for mixed effects.

Three different tissue effects can be exerted on the target tissue: cutting, fulguration and desiccation (Figure 5).

For electrosurgical cutting, the electrode is used in a non-contact mode. Current arcs to the tissue creating a spark (ionized stream) that directs intense heat (approximately 400° C) to tissue over a very limited surface area and vaporizes the intracellular content.

Fulguration is a tissue effect achieved by sparking the coagulation waveform to tissue in a non-contact mode. The energy application is of higher voltage than used for cutting but is intermittent. This will induce proteins to melt and form a coagulum, resulting in hemostasis. This setting is used to control oozing capillary beds in delicate, heat-sensitive tissues or to ablate neoplastic tissue.

Electrosurgical desiccation occurs when the coagulation waveform is used in contact mode. Contact with the tissues decreases voltage leading to less heat production, drying of the tissues and proteins melting, and the formation of a coagulum. This last effect can also be achieved indirectly via energy transfer to hemostatic forceps. Hemostasis is efficient for arteries up to 1 mm and veins of even 2 mm diameter. Collateral damage can occur up to 2 cm from the coagulation site.

Figure 5. Illustration of the different uses of monopolar electrocoagulation: A. coagulation of larger vessels is achieved in contact mode (desiccation); B. hemostasis of the capillary bed is achieved by creating a coagulum in non-contact mode (fulguration). Applications

Companion animal

Electrosurgical skin incisions have been shown to decrease operative time, blood loss and postoperative pain when compared to scalpel incisions. The correct power setting of the instrument and speed of moving the electrosurgical pen are essential to avoid abundant collateral thermal tissue damage that might impair healing. Capillary hemostasis is accomplished by moving the tip of the electrosurgical pen in the vicinity of a bleeding vessel and allowing a spark to coagulate the tissue. Bigger vessels are grasped with a hemostat and the monopolar electrosurgical pen is brought into contact with the metal instrument. The hemostat will act as an extension of the metal electrode tip and the vessel will thus be coagulated. During endoscopic surgical procedures tissue dissection is performed using J- or L-shaped monopolar electrode extensions (for example during cholecystectomy). For stronger tissues the monopolar electrosurgical generator can be connected to endoscopic scissors. The scissors will then act as a monopolar electrosurgical pen, coagulating the tissue brought into contact with them (Figure 6). After deployment of the current, the coagulated tissue can be cut without the need for changing the instrument.

Figure 6: Attaching the electrosurgical generator to (endoscopic) scissors allows the combined use of electrosurgical coagulation and mechanical cutting.


Making the skin incision using a monopolar electrosurgical pen is also used in large animals (horses). High power settings are needed to achieve sufficient hemostasis at the level of the large subcutaneous blood vessels. In consequence, delayed healing of the skin is expected. This type of electrosurgery is therefore often restricted to incisions that are left to heal per secundam (e.g. removal of large skin tumors).

Exotic animals

For larger exotic animals, comparable in size to dogs and cats, monopolar electrosurgical techniques can be used. The same principles and techniques, as described above for companion animals, apply. Disadvantages

Burns at the return pad remain a concern. The patient electrode should have a wide contact area so as to reduce the chance of concurrent concentration and patient burning (Figure 7). Malleable grounding pads are better in this regard when compared to the metal grounding plates used historically. Modern generators are therefore equipped with contact quality monitoring or return electrode monitoring: in case of improper return electrode contact they stop the current to prevent unwanted thermal damage.

Figures 7A. A patient burn wound and charred operating table cover caused by a direct coupling injury (lack of contact with the patient return pad) is detected after surgery.
Figure 7B. 7B. A burn wound in a patient that had direct contact with the metal table instead of the return pad.

In addition, the efficiency in acquiring hemostasis is only limited when the surgical field is wet. Also, when the electrode is used for making skin incisions, it is more difficult to control the depth of the incision compared to scalpel incisions.

The high temperature produces substantial amounts of smoke, limiting visibility during endoscopic procedures. The smoke plume resulting from the vaporization of tissue contains dangerous biological (viral, bacterial) and chemical (carcinogenic) substances. Laparoscopic use of monopolar electrocoagulation has the added risk of insulation failure and damage to surrounding organs caused by sparks.

Because current flows through the patient’s body, the use of monopolar electrosurgical techniques is contraindicated in patients with a pacemaker or other high-tech implantable devices (as middle ear and cochlear implants).

4.1.4 Bipolar electrocoagulation and electrosurgery Technique

Bipolar electrosurgery differs from monopolar electrosurgery in the sense that the current flow does not pass through the patient. Instead, current flows from one tip of the instrument (active electrode) to the other tip (passive electrode, Figure 8). Only tissues in contact with both tips of the instrument will receive current, allowing the desired tissue effect to take place with much less energy (30-50 W) and thus less risks for the patient.

Figure 8. Electric current generated in the electrosurgical generator flows to the active electrode, passes through grasped tissue and returns via the passive electrode to the generator.

Bipolar instruments exist in two basic forms: forceps and scissors (Figure 9). The hand instrument is activated by a hand or foot switch or by an automated function that activates the generator when conduction between the two tips is possible.

The bipolar forceps (much resembling normal tissue forceps) are effective in use for hemostasis since tissue grasped between its tips will be coagulated. The hemorrhaging vessel can be grasped between the tips of the forceps or the open tips can be placed on tissue, coagulating the superficial capillary bed in between them. Bipolar scissors are used to sever tissue while at the same time coagulating them. Modifications of these two instruments are available for endoscopic procedures.

Precise placement of the instrument allows effective coagulation of small vessels (≤ 3 mm diameter). Lateral thermal damage can occur up to 8 mm from the point of application.

Figure 9. Bipolar electrocoagulation is performed with forceps- or scissor-type hand instruments. Applications

Companion animal

Bipolar forceps are used for hemostasis in general surgeries (Figure 10) as well as in specific endocrine, cardiac or neurosurgical procedures. Active bleeding vessels are grasped and coagulated, and tissues can be coagulated prior to transection. Bipolar scissors are used to facilitate elaborate tissue dissection as needed during orthopedic (limb amputations) or oncological procedures (en-bloc resections). Endoscopic bipolar forceps and scissors are used in many laparoscopic (endoscopy of the abdominal cavity) procedures where transection of tissues is necessary (ovariectomy, ovariohysterectomy, orchiectomy, cryptorchidectomy), as well as in thoracoscopic (endoscopy of the chest cavity) procedures (opening of the mediastinum, pericardectomy).

Figure 10. Bipolar forceps used to achieve hemostasis during a prescrotal orchiectomy in a dog.


The use of bipolar forceps in horses is severely limited by the size of the vessels in the operative field. Its successful application is described in equine laparoscopic ovariectomy and equine cryptorchidectomy. During oncological procedures they can be used to achieve hemostasis of capillaries and smaller vessels.

Exotic animals

For larger exotic animals, comparable in size to dogs and cats, bipolar electrosurgical techniques can be used (Figure 11). The same principles and techniques, as described above for small animals, apply.

Figure 11. Bipolar forceps used to achieve hemostasis in an Iguana with dystocia. Disadvantages

Standard bipolar forceps take longer to coagulate a vessel compared to monopolar electrocoagulation. They tend to stick to carbonized tissue, which can result in disruption of the vessel seal when the forceps are removed. Closing the bipolar forceps completely, allowing both metal tips to actually come into contact with each other, leads to short circuiting. There will be no current flowing through the tissues and therefore no thermal tissue effect. Releasing the forceps will result in continuation of bleeding. Damage to the insulation material of bipolar scissors will also often lead to short circuiting.

4.1.5 Radio wave radiosurgery Technique

The radio wave radiosurgery generator (Figure 12) converts alternating current to high frequency direct current and extensively modifies and filters the resulting waveform. It operates at frequencies 10 times higher than typical electrosurgical generators. There is no need for intimate contact between the patient and the return pad since the emitted radio waves are collected via the wire antenna part of the return plate and directed to the generator.

Electrodes are manufactured in various lengths and shapes: fine-tipped electrodes deliver a very high current density resulting in precise cutting with minimal coagulation, a broad spatula-shaped electrode will deliver a lower current density resulting in desiccation or fulguration of tissue, and a loop electrode is used to scrape of layers of tissue (dissection, trimming of granulation tissue, removal of narrow-based masses).

Figure 12. The radio wave radiosurgery generator can be equipped with bipolar forceps/scissors and comes with a variety of monopolar electrode extensions suited for specific purposes. Applications

Companion animal

Radio wave radiosurgery devices are popular for oral surgical procedures (removal of gingival hyperplasia, benign oral tumors). Veterinary dermatologists, also, often use them to remove small, benign dermal proliferations.

Large animal

No specific indications.

Exotic animals

The reduced need for contact between the patient and the return plate, in combination with the ability to make precise, low-power incisions with minimal char, make these devices ideally suited for work on avian and small exotic species. Disadvantages

The emitted radio waves can be disruptive to the normal functioning of operating room monitoring equipment (ECG, video monitors). The same concerns regarding the use of electrical current in an operative setting exist for the use of radio waves (Figure 13).

Figure 13. This rabbit’s fur was set on fire after applying an energy-based device in the presence of a surgical field still wet from an alcoholic disinfectant.

4.1.6 Vessel sealing Technique

An improved form of bipolar electrosurgery has been developed for the purpose of secure vessel sealing only (LigaSure, Medtronic, Figures 14-15). This system operates at high current and low voltage. The tissue grasped between the electrode ends is compressed and locked. On activation, current passes from the active electrode through the grasped tissue to the passive electrode and back to the generator. The generator monitors tissue impedance and adjusts energy output to achieve hemostasis with less heat and minimal tissue carbonization. The result is welding of vessel collagen and elastin to form a translucent seal. Vessels as large as 7 mm in diameter can be sealed and will withstand three times systolic blood pressure. Lateral thermal damage occurs at 1.5-6 mm from the application site.

Figure 14. The Force Triad device (Medtronic) combines monopolar and bipolar electrocoagulation together with vessel sealing technology in one generator.

A great advantage of this system is that vessels do not need to be isolated from the surrounding tissues. This decreases surgical time and avoids potential dissection-related complications. There is no learning curve for use of the instrument since the energy cycle is electronically guided with an auditory signal at completion, instead of being operator dependent.

Some endoscopic forceps have a built-in knife that is used to cut the grasped tissue after completing the energy cycle (Figure 15).

Figure 15: Vessel sealing forceps for: A. minimally invasive surgery and B. conventional surgery (Medtronic). Applications

Companion animal

Vessel sealing instruments can be used during many conventional surgical procedures. Their benefit will be most pronounced in procedures where numerous ligatures need to be placed (splenectomy; resection of a spleen) or during dissection of delicate vascular tissues (adrenalectomy; resection of an adrenal gland or in an ovariectomy; Figure 16). In endoscopic surgery a 5- or 10-mm instrument with combined sealing and cutting function is used in common procedures, such as laparoscopic castration (severing the ovarian pedicle or the spermatic cord of abdominal testes) and thoracoscopic exploration (mediastinal dissection), as well as more advanced techniques (thoracoscopic pericardectomy).

Figure 16: The LigaSure hand instrument used for canine ovarian pedicle coagulation.

Large animal

Because of the ability to achieve hemostasis in large vessels, this instrument is ideally suited for use in large animals. It has many applications in conventional procedures (e.g. cutting the mesentery during enterectomy in the horse). The vessel sealing system is also used during laparoscopic procedures, such as ovariectomy or cryptorchid castration in horses.

Exotic animals

Vessel sealing instruments can also be used in small mammals. Indications are adrenalectomy in ferrets and castration procedures (ovariectomy, ovariohysterectomy or orchiectomy) in larger rodents or reptiles. Disadvantages

The instrument’s jaws may adhere to tissue and result in disruption of the seal during device removal. Thermal collateral damage should be considered when working near heat-sensitive structures. Although the costly hand instruments can be resterilized with gas (ethylene oxide) or plasma (hydrogen peroxide), their lifespan remains limited.

4.2 Cryosurgery

4.2.1 Introduction

Cryosurgery is the destruction of tissue by repeated cycles of controlled freezing and thawing. Freezing causes direct tissue damage by the formation of ice crystals and delayed tissue damage by vascular stasis, thrombosis and secondary ischemia. Tissue sensitivity to cryonecrosis will be dependent on its water content, cellularity and vascularity.

Freezing tissue to a temperature of -20°C results in the formation of intracellular crystals that rupture the cell’s outer membrane, whilst extracellular crystals lead to cellular dehydration; both result in cell death. Rapid freezing causes the greatest development of intracellular crystals. During slow thawing the phenomenon of recrystallisation occurs, during which crystals grow in size, increasing their damaging potential. Because pre-cooled tissue freezes faster than normal tissue, the freezing-thawing cycle is repeated once to maximize the necrotic effect.

After frost-induced necrosis, the underlying tissue recovers, going through the usual phases of inflammation, granulation, and epithelialization. Scar tissue formation is less when compared to that formed after burning.

4.2.2 Technique

Since success of the treatment depends on rapid freezing of the tissue, the cryogen needs to deliver extremely cold temperatures. In veterinary medicine liquid nitrogen (-196 °C) and nitrous oxide (-89 °C) are used more commonly than carbon dioxide (-79 °C).

There are different application techniques for freezing tissue:

  • Spraying steam (Figure 17) and droplets (liquid nitrogen) or pouring a liquid (carbon dioxide) directly on the tissue. This is the most effective application method, since evaporation of the liquid cryogen on the tissue surface (usually skin) removes a great amount of heat from the treated tissue.
  • Application via a contact probe that is either cooled by circulating liquid cryogen (liquid nitrogen) or by releasing a high-pressure gas through a small orifice in the tip (nitrous oxide). This allows better control of the area to be frozen and also achieves deep freezing. Post-incisional placement of the probe deep in a lesion permits freezing of masses from the inside.
  • A metal probe or cotton tip can be immersed in the cryogen (liquid nitrogen) and applied directly onto the tissue. This technique is only sufficient for small and superficial dermatological or ophthalmological lesions.
Fig 17A. cryospray steam applied to the leg of a horse and B.
Figure 17B. A contact cryoprobe used on the eye of a horse.

Monitoring the temperature of the treated area is essential since only 75% of the tissue frozen to -20°C will actually be destroyed. Visual inspection and manual palpation are not reliable for assessment because the outer edge of the ice ball is only 0°C. Instead, thermocouple needles can be inserted around the target area prior to application of the cold source. This allows accurate assessment of the induced necrosis, while preventing collateral damage to surrounding delicate tissues (muscles and nerves).

4.2.3 Applications

Companion animals

Benign cutaneous and neoplastic lesions are common in older animals. Cryosurgery is popular for their treatment since it can be performed without general anesthesia and on an outpatient basis. Some sedation or a local analgesic (when epinephrine is added this will enhance cryonecrosis through induced vasoconstriction) is used to counteract pain at the time of application.

Cryosurgery is also popular in ophthalmic surgery: a sterile surgical field is not required, and the fibrous support tissues of the eye are relative cryoresistant. General anesthesia is necessary to prevent unwanted movement during the procedure. Palpebral tumors, dermoids, distichiasis and corneal melanocytes can be successfully treated or destroyed. Glaucoma can be treated by transsceral focal destruction of the ciliary body (cyclocryotherapy).

Cryosurgery is further described as an adjunctive therapy in perianal fistulas and for the palliation of clinical signs in patients with oral tumors. Cryosurgical instruments can be guided through endoscopes and used for tumor destruction or palliation in luminal organs (bladder, urethra, colon, etc.).

Large animals

Common indications for cryosurgery in horses include the treatment of sarcoids (the most common skin tumor in this species). In addition, ocular tumors (e.g. squamous cell carcinoma) can be successfully treated using this technique.

Exotic animals

The most common indication for cryosurgery in birds is the resection of a cloacal papilloma. The high vascularization of the cloacal region makes traditional surgery less desirable because of the expected amount of hemorrhage.

4.2.4 Disadvantages

When cryosurgery is used for tumor ablation it is imperative to take tissue biopsies of the tumor and to drain lymph nodes prior to the procedure for tumor identification, grading and staging. In addition, verification of complete tumor removal with adequate margins necessitates taking post-cryosurgery biopsies.

Disadvantages of cryosurgery are the development of swelling (resolves within 48 hours to 1 week), the possibility of post-operative hemorrhage (in ulcerated tissues or via biopsy sites), the occurrence of a necrotic crust (sloughs between 2-8 weeks), depigmentation and the absence of hair regrowth in the treated area.

The surgeon should perform cryosurgery with care, as frost-burn lesions may easily occur during spillage or undesired spray effects. Accumulation of vaporous products leads to dangers of combustion or the potential for damaging the environment.

Freezing a tumor with major bony involvement may lead to a spontaneous fracture (destroying the cellular elements reduces bone strength by 70%) or to nitrogen embolism when liquid nitrogen is sprayed directly to cancerous bone.

4.3 Laser surgery

4.3.1 Introduction

Laser is the acronym for Light Amplification by Stimulated Emission of Radiation. Stimulated emission occurs when atoms in the lasing medium, excited to a higher energy state, return to their ground state and release the absorbed energy in the form of photons. Laser light typically contains a single wavelength (monochromatic), is nondivergent (collimated) and all parallel waves of laser light move in phase, reinforcing each other as they travel through space (coherent).

Interactions between laser light and tissue are divided into photochemical, photothermal and photomechanical, based upon whether the laser energy is converted to chemical energy, thermal energy or acoustic energy, respectively.

  • The photochemical effect occurs at low power densities (0.001-1 watt/cm2) and arises when a specific light wave induces a chemical reaction (e.g. adhesive curing of dental resins). In photodynamic therapy, laser light acts as an energy source to trigger a photochemical reaction. First, a tumor-specific photosensitizer is administered that will selectively bind tumor cells or that will exclusively be metabolized in tumor cells. The tumor is then exposed to laser light too low in energy to have a thermal tissue effect, but high enough to activate the photosensitizer. Upon activation the photosensitizer initiates a cascade of reactions, leading to the release of oxygen radicals that will destroy tumor cells. This technique is directed solely against tumor cells and avoids accidental damage to adjacent structures (i.e., highly specific).
  • Photothermal laser-tissue interactions occur when laser light is absorbed and converted to heat within the tissues (1-107 watt/cm2). The heat generated depends on the power setting (in watts or joules), the tissue exposure time, the modality used (contact or noncontact), and the absorption coefficient of the target tissue. Focusing the laser light delivers high-energy amounts in one specific place with minimal collateral heat. The result is precise cutting or even vaporization of tissue.
  • Photomechanical or photoionization occurs at high power levels (108-1012 watt/cm2) and results in direct tissue destruction through cell lipid bilayer membrane, protein and DNA destruction.

When laser light is focused on tissue it may be reflected, absorbed, scattered or transmitted through the tissue, depending on the physical characteristics of the laser light (wavelength, frequency and power) and the composition of the irradiated tissue (water, hemoglobin and melanin content).

Compared to conventional surgery, laser surgery leads to superior hemostasis, less post-operative swelling and decreased post-operative pain.

4.3.2 Technique

The lasing medium, which can be a solid crystal (neodymium or holmium), a liquid or a gas (carbon dioxide), determines the wavelength of laser light. The wavelength ranges from visible infrared to ultraviolet. Apart from its wavelength, the effect of the laser is determined by its energy production. Large appliances, such as those used in human medicine, may generate over 100 W. For use in companion animal medicine, 20 W is often sufficient. Laser systems used for medical purposes may be set either to continuous or pulsating light emission.

The most commonly used laser systems in veterinary medicine are the carbon dioxide (CO2) laser, the neodymium:yttrium aluminium garnet (Nd:YAG) laser and the diode laser.

  • Carbon dioxide lasers have a wavelength of 10.600 nm, which is well absorbed by water. The tissue effect is superficial (0.1-1mm) and the hemostatic potential is moderate. The focused beam will result in a precise incision with only little thermal damage to the wound margins. Adjusting the laser beam to a scattered effect will create hemostasis by coagulation or even remove tissue by photo-evaporation. In CO2 lasers, the infrared light (invisible to the human eye) is conducted to the target tissue using articulating hollow tubes with built-in mirrors. This unfortunately limits its application.
  • The Nd:YAG laser, with a wavelength of 1064 nm, is less absorbed by water. It therefore has a greater depth of penetration (up to 3 mm), creates more thermal damage and has a stronger hemostatic effect (capillaries and larger vessels). This laser is mainly used for tissue evaporation. Equipped with a focusing adapter, the laser can also be used to make incisions. A targeting laser (Helium-Neon) is added to visualize the beam for practical reasons. The laser beam can be guided through flexible quartz fibers allowing trans-endoscopic use (Figure 18).
  • The diode laser produces a beam with a wavelength between 600-1600 nm. It is comparable to the Nd:YAG laser in its tissue effect. The diode laser is often used in contact mode, reaching high temperatures at the tip and resulting in coagulation and tissue resection with limited lateral effect (< 0,1 mm). Its beam can also be guided through quartz fibers. The diode laser is popular because it is compact, user-friendly and economical.
Figure 18. Nd-YAG laser used to resect a vulvar tumor in the dog.

4.3.3 Applications

Companion animals

Photodynamic therapy is used merely for oncological purposes in the treatment of prostate carcinomas and superficial skin and oral tumors. Adhesive curing of dental resins is a routine part of orthodontic reconstructive surgery (dental fractures, malocclusions).

Carbon dioxide lasers are used in surgical oncology for skin incisions, tumor dissection or tumor ablation for curative or palliative intent (skin, tongue, perianal, ear canal, nose). In upper respiratory tract disorders CO2 lasers are successfully used for shortening an elongated soft palate or removing nodules from the vocal cords. Endoscopic application of Nd:YAG or diode lasers is used during ovariectomy (transection of the ovarian pedicle), the resection of polyps from the gastro-intestinal tract or redirecting the opening of an intramural ectopic ureter.


In horses, laser surgery is used for the treatment of various conditions of the upper respiratory tract, such as ethmoidal hematomas, epiglottal cysts or guttural pouch tympany. These procedures can be performed in the standing, sedated, horse with topical anesthesia on the mucosa. The laser energy is delivered through the laser fiber, which is passed through the instrument canal of an endoscope. The CO2 laser can be used to make skin incisions or for the dissection of tumors (equine sarcoid, squamous cell carcinoma).

Exotic animals

Photodynamic therapy can be used for the treatment of squamous cell carcinomas.

4.3.4 Disadvantages

Laser beams are highly energetic and easily reflected, and it is therefore imperative to take the necessary safety measures to protect the patient, surgeon and personnel in the surgical theatre:

  • The surgical theatre should not have any transparent windows in order to protect passers-by from exposure to laser light
  • All personnel present in the theatre should wear laser-specific protective goggles/glasses
  • The tracheal tube needs to be protected from laser energy during oropharyngeal application as the high oxygen concentration poses a real risk for combustion
  • The smoke plume resulting from the vaporization of tissue contains dangerous biological (viral, bacterial) and chemical (carcinogenic) substances
  • Because CO2 laser energy is highly absorbed by water, protection of the patient is possible by covering delicate exposed parts with wet towels.

4.4 Endoscopic surgery

4.4.1 Introduction

 Endoscopic procedures (Figure 19) allow access to, and visualization and manipulation of tissues or organs of interest in body cavities or body spaces without the need for large incisions through the tissues covering them. Video cameras and specialized equipment for the handling of these tissues allow for minimally invasive surgery (MIS). When an endoscopic procedure is combined with a mini-celiotomy or mini-thoracotomy for improved exposure, this is referred to as video-assisted surgery (VAS).

Figure 19. Illustration of the two different types of endoscopic surgery: A. laparoscopic-assisted cryptorchidectomy in a dog (video-assisted procedure) and B. laparoscopic cholecystectomy in a dog (minimally invasive surgery).

A basic endoscopy set consists of an endoscope, a camera, a light source and a monitor (Figure 20). The endoscope is connected to a camera that processes the image and sends it to a monitor. A strong light source, necessary for good visualization, is connected to the endoscope with a fiberglass cable. Digital recording devices may be added to the viewing circuit in order to log pathological lesions or surgical interventions. Depending on the type of procedure, insufflation of the cavity or space entered, with air, CO2 or saline will be needed to create a working environment. 

Figure 20. Basic endoscopic components consist of the camera (top left), light source (middle left), insufflator (bottom left) and the monitor (right).

Endoscopes can be flexible or rigid.

  • A flexible endoscope is designed to be passed directly into a natural orifice and to explore the luminal side of the organ system (respiratory, gastrointestinal or urogenital tract).
  • Rigid endoscopes can also be passed into a natural orifice to explore the luminal side provided this lumen runs straight (nasal passages, trachea, ear canal, vagina, female urethra). Additionally, rigid endoscopes can be passed through percutaneous cannulas, allowing inspection of cavitary organ systems (bladder, joints, abdominal or thoracic cavity).

Because procedures can be performed without the large incisions typical of conventional surgery, patients benefit from a smaller surgical wound with less post-operative complications (in particular wound infections, wound dehiscence, bleeding, seroma formation, abdominal herniation); less surgical trauma, resulting in decreased peri- and post-operative pain; a faster recovery with decreased hospitalization; less adhesions and a better cosmetic result. The surgeon benefits from the improved visualization and magnification on the monitor, which will increase diagnostic accuracy.

To perform surgical procedures and use minimally invasive surgery to its full potential, particular skills and experience are needed. Dry- and wet-lab training of these techniques is strongly encouraged.

4.4.2 Technique

Endoscopy with a flexible endoscope is performed by applying lubricant to the endoscope and subsequently passing the scope into the desired lumen. To avoid the lumen from collapsing around it, air is insufflated through the endoscope. Endoscopy of the gastrointestinal tract allows visualization of the esophagus, the stomach and the proximal part of the intestines (gastroduodenoscopy). The rectal approach allows inspection of the distal gastrointestinal tract (colonoscopy). The flexible endoscope has a working channel along which different instruments can be passed. Endoscopy of the respiratory tract includes inspection of the nasal cavities (rhinoscopy), of the trachea (tracheoscopy) and of the larger bronchi (bronchoscopy).

Otoscopy (Figure 21) allows visualization of the ear canal and tympanic membrane. Pathological changes are easily recognized due to the magnification and can be seen not only by the operator but also by assistants, students or even animal owners. The working channel allows passage of endoscopic instruments (suction/irrigation, biopsy forceps, grasping forceps, myringotomy needle).

Figure 21. Otoscopic removal of a middle ear polyp in a cat.

Vaginocystoscopy utilizes a rigid endoscope with fluid irrigation to distance the luminal structures.

For arthroscopy the joint space is dilated by pressurized infusion of saline. A hollow cannula filled with a blunt trocar is placed through a stab incision inside the joint. The trocar is retracted and replaced by an endoscope to allow visualization of intra-articular structures. When needed additional cannulas are placed for the introduction of instruments (palpation probes, curettes, burrs).

Thoracoscopy makes use of the free space that develops after the creation of a pneumothorax. Patients are positioned in dorsal or lateral recumbency and the endoscope is placed paraxiphoidally or intercostally, respectively.

For laparoscopic procedures it is necessary to inflate the abdomen to create a working environment. This is most commonly done with CO2 gas. Cannulas are placed in the ventral or lateral abdomen, the number and exact location depending on the type of procedure. Laparoscopic-assisted procedures use the endoscope to localize the problem and then bring it extra-corporeal through a mini-celiotomy.

4.4.3 Applications

Companion animal

Flexible endoscopy of the gastrointestinal tract is commonly performed. Esophagoscopy, gastroduodenoscopy and colonoscopy are part of the diagnostic work up of patients with chronic vomiting and diarrhea. Mucosal biopsies can be taken, and marginal resection of polyps is possible with the use of electrosurgical loop snares. The endoscope can also aid in placing gastric feeding tubes. Endoscopy is very successful (90%) in removing obstructing esophageal foreign objects.

Flexible endoscopy of the lower respiratory system allows inspection, removal of foreign objects and biopsy (histology, bacterial, mycotic) of suspected lesions. Rigid endoscopes are used for tracheoscopy (tracheal collapse, tumors) and rhinoscopy (foreign bodies, diagnosis of nasal pathologies (aspergillosis, tumors).

Otoscopy can be used to remove foreign bodies, diagnose ear canal tumors, extract middle ear polyps, and diagnose and treat middle ear disease (myringotomy).

Vaginocystoscopy is performed to diagnose congenital abnormalities of the urogenital system (persistent hymen, ectopic ureters) or developmental disorders (uroliths, polyps or tumors).

Arthroscopy of the elbow is used for diagnosis and treatment of elbow dysplasia. Cartilage flaps in shoulder OCD are arthroscopically removed and meniscal injuries or OCD lesions in the knee can be visualized and treated. Arthroscopy is also used for the minimally invasive repair of intra-articular fractures (verification of fragment apposition).

Thoracoscopy assists in the diagnosis of pathological conditions such as spontaneous pneumothorax (blebs/bullae), pyothorax (migrating grass awns) and pleural effusion (mesothelioma). The most commonly performed thoracoscopic procedure is subtotal pericardectomy, but its use has also been reported in thoracic duct ligation (chylothorax), correction of a persistent right aortic arch or persistent ductus arteriosus, partial lung lobe resection and many other procedures.

Laparoscopic exploration allows biopsies to be taken from the liver, gallbladder, kidneys, prostatic gland, lymph nodes, spleen and any intra-abdominal tumor. Laparoscopic-assisted biopsies from intestines and the reproductive tract are also possible. Laparoscopic-assisted placement of feeding tubes, incisional gastropexy for prevention of gastric dilatation/volvulus, removal of cryptorchid testis, ovariohysterectomy and resection of intestinal tumors can be performed. Laparoscopic ovariectomy, cholecystectomy, adrenalectomy, attenuation of portosystemic shunts and insulinoma resection have all been described. During laparoscopic abdominal exploration the endoscope can even be advanced into the bladder, allowing for removal of cystic calculi or polyps.


In horses, endoscopic surgery of the upper airways is often performed for diagnostic or therapeutic purposes. Cystoscopy can be performed in female and male patients to identify uroliths. Hysteroscopy in the mare is performed to diagnose and treat abnormalities of the uterine mucosa (e.g. cysts).

For diagnostic purposes laparoscopy is performed in the standing or recumbent animal, depending on where the abnormality is located. Common uses for laparoscopy are diagnostic laparoscopy, cryptorchidectomy, ovariectomy and diagnostic thoracoscopy. Other reported uses include inguinal hernia repair, ruptured bladder repair and ventral colopexy. Laparoscopy is often used for cryptorchid castration and ovariectomy (in the standing horse).

Exotic animals

Endoscopy is extensively used in avian medicine. Due to the presence of the air sac system no insufflation is necessary when performing an avian celioscopy.

The initial role for this instrument was to determine the sex of monomorphic species (such as parrots). The approach would always be on the left lateral side, as this is where the single ovary of birds can be found. For endoscopic evaluation of the coelom (Figure 22), the left lateral approach is still most commonly used. The 2.7 mm endoscope with a 30° angle view is considered the standard in avian endoscopy. The 30° angle view allows evaluation of a larger area without having to move the endoscope around. The scope is used in conjunction with a working channel, which enables the introduction of fine instrumentation for cutting and taking biopsies. Many different instruments have been developed specifically for use in birds.

Tracheoscopy is a very important technique to evaluate and treat the commonly seen tracheal obstructions in parrots caused by a fungal infection. To maintain anesthesia and oxygen flow into the respiratory system, air sac perfusion anesthesia has to be performed. This will enable free access to the trachea without the risk of suffocation. The trachea is usually not large enough to accommodate a working channel but will function as a working channel for the endoscope. For a tracheal obstruction in a parrot the size of an Amazon parrot (approximately 450 gram), a 1.9 mm scope with a 0° angle view is considered ideal. The small sized scope will allow the introduction of grasping forceps in the trachea alongside the scope, thus allowing removal of the obstruction.

Triple-entry endosurgery techniques have been described for avian medicine, but this should be considered a highly specialized area of surgery.

Endoscopic ovariectomy has also been performed in rabbits and ferrets. It is controversial, however, as this technique does not have a clear advantage over traditional surgery.

Endoscopy is also a great tool in reptiles, and especially in turtles. This technique prevents the need to saw through the plastron (lower shell of a turtle) to enter the coelom. Insufflation of the coelom is necessary in these species. Endoscopic-assisted ovariectomies have been described in turtles.

Endoscopy is also a great tool in the evaluation of the respiratory system in many different species of reptile.

Figure 22. Endoscopic evaluation of the coelom in a pigeon.

4.4.4 Disadvantages

The most common complications of endoscopic surgery occur during placement of the trocar-cannula combinations. Cartilaginous trauma can occur during arthroscopic procedures. Laceration of parenchymatous organs (spleen, liver) and perforation of luminal organs (bladder) can occur during laparoscopic procedures. Laceration of lung lobes and perforation of blood vessels or even the heart can occur during thoracoscopic procedures.

Many horses show a transient rise in rectal temperature and some abdominal discomfort after a laparoscopic procedure with CO2-induced pneumoperitoneum of longer duration. The risk of perforating (gas filled) intestines when introducing a trocar at the beginning of the procedure is real. Fasting for 36 hours before surgery is recommended to reduce this risk.

4.4.5 Health risks for the surgical team

The surgeon should be aware of the ‘chimney effect’: leakage of CO2 gas may occur around the cannula opening. When utilizing electrosurgical devices or lasers, the risks mentioned earlier relating to surgical smoke (irritation, mutagenic effect and transport of infectious pathogens) therefore also apply. If laser surgery is used for endoscopic tumor resection, the possible implantation of tumor cells near the trocar opening should be taken into account.

Endoscopy combined with electrosurgery or laser surgery in large animals will generate large amounts of carbon monoxide (CO) in the body cavities due to a chemical reaction with the carbon dioxide (CO2) present. This is of risk to the patient but also to the surgical team. In the patient, it may lead to methemoglobinemia and possible saturation problems.

4.5 References

Bartels, K.E., 2002. Lasers in veterinary medicine–where have we been, and where are we going? The Veterinary clinics of North America. Small animal practice, 32(3), 495–515.

Davidson, E.B. et al., 2001. Evaluation of carbon dioxide laser and conventional incisional techniques for resection of soft palates in brachycephalic dogs. Journal of the American  Veterinary Medical Association, 219(6), 776–81.

Divers, S.J., 2010a. Exotic mammal diagnostic endoscopy and endosurgery. The Veterinary Clinics of North America Exotic Animal Practice, 13(2), 255–72.

Divers, S.J., 2010b. Reptile diagnostic endoscopy and endosurgery. The Veterinary Clinics of North America Exotic Animal Practice 13(2), 217–42.

Dubiel, B. et al., 2010. Electromagnetic energy sources in surgery. Veterinary Surgery, 39, 909–24.

Podkonjak, K.R., 1982. Veterinary cryotherapy-1. A comprehensive look at uses, principles, and successes. Veterinary Medicine, 77(1), 51–64.

Sackman, J.E., 2012. Surgical Modalities: Laser, Radiofrequency, Ultrasonic, and Electrosurgery. In K.M. Tobias & S.A. Johnston (eds.), Veterinary Surgery Small Animal. St. Louis: Elsevier Saunders, pp. 180–86.

Smith, T.L. & Smith, J.M., 2001. Electrosurgery in otolaryngology-head and neck surgery: principles, advances, and complications. The Laryngoscope, 111(5),.769–80.

Van Lue, S.J. & Van Lue, A.P., 2009. Equipment and instrumentation in veterinary endoscopy. Veterinary Clinics of North America: Small Animal Practice, 39(5), 817–37.

Withrow, S.J., 1980. General principles of cryosurgical technique. The Veterinary Clinics of North America Small Animal Practice, 10(4), 753–97.


Dr. Bart van Goethem graduated from Ghent University and then worked for some years in private practice. He had his specialist surgical training at Utrecht University and later also completed a Ph.D. there. After working in referral practices, he returned to Ghent University, where he currently holds the position of Head of Surgery Clinics. He is an enthusiastic international lecturer and propagator of minimal invasive surgery, has medical publications (45+), wrote book chapters (4), and acts as a reviewer for scientific journals (7).

Dr. Jos Ensink, DVM, Ph.D., Diplomate ECVS, graduated from the Utrecht University Faculty of Veterinary Medicine, The Netherlands, in 1987. In the same year, she started her internship, followed by her residency at the Dept of General and Large Animal Surgery of Utrecht University, later Department of Equine Sciences. In 1995 she got her Ph.D. with the thesis entitled “Pharmacokinetics and clinical aspects of oral broad-spectrum penicillins in the horse.” Since 1994 she is a specialist in Equine Surgery of the RVNA, and in 1997 she became a Diplomate of the ECVS (Large Animal Surgery). Her primary clinical and research interests are soft tissue surgery, oncology, and ophthalmology.

Dr. Nico Schoemaker graduated from the Faculty of Veterinary Medicine in Utrecht in 1994. After graduation, Nico did an internship in Companion Animal Medicine at the Department of Clinical Sciences of Companion Animals and a Residency in Avian Medicine and Surgery at the same University. His residency led to certification as an avian specialist in the Netherlands, Europe, and the USA. In 2003 he defended his Ph.D. entitled; Hyperadrenocorticism in ferrets. He has ever since been working at Utrecht University at the Division of Zoological Medicine. His work involves seeing exotic animal patients, teaching both undergraduates and graduate students, and performing research with a focus on clinically relevant topics in small mammals and birds. Within the European College of Zoological Medicine, he is a founder diplomate of the small mammal specialty and a past-president.

Chapter 5 Suture materials and suture techniques

Jolle Kirpensteijn, DVM, PhD, Dipl. ACVS & Dipl. ECVS (Small Animal)

Gert ter Haar, DVM, PhD, Dipl. ECVS (Small Animal)

with contributions from

Jos Ensink, DVM PhD, Dipl. ECVS (Equine)

Freek J. van Sluijs, DVM, PhD, Dipl. ECVS (Small Animal)

Based on the previous edition of and with contributions from

Rien M.A. van der Velden, DVM, PhD

5.1 Suture materials

            5.1.1 Introduction

            5.1.2 Suture materials

               General suture materials

               Specific suture materials

            5.1.3 Suture needles

            5.1.4 Staples and clips

5.2 Suture techniques

            5.2.1 Introduction

            5.2.2 Handling needle holder, needle and suture

            5.2.3 The surgical knot

               Knot tying with instruments

               Knot tying by hand

               Cutting the sutures

            5.2.4 Interrupted suture patterns

               Simple suture

               Horizontal mattress suture

               Vertical mattress suture

               Cross-stitch or cruciate suture

            5.2.5 Continuous suture patterns

               Simple continuous sutures

               Lock-stitch suture

               Continuous mattress suture

               Continuous subcutaneous or subcuticular suture

               Far-near patterns

            5.2.6 Specific sutures for hollow organs

               The simple interrupted approximating technique

               The crushing technique

               The Schmieden suture

               The Lembert suture

               The Cushing suture

               Uterine suture (Utrecht method)

               Single or double suture layer

               Parker-Kerr suture

               Non-perforating purse-string suture

5.3 References and further reading

5.1 Suture materials

5.1.1 Introduction

Suture material, in its broadest definition, includes all materials that can be used to permanently close a surgical wound and/or stop bleeding from vessels, such as sutures, staples and (hemo)clips, and the needles needed to pass suture through the tissue.

5.1.2 Suture materials General suture materials

Suture materials may be classified in different ways; for instance, natural materials (catgut) can be differentiated from synthetic materials. A practical and clinically more useful classification is based on structure and absorbability. A differentiation is made between absorbable and non-absorbable and braided (multifilament) and single strand (monofilament) suture material. Applied to a number of well-known suture materials, this gives the following classification (Table 1):

Table 1. Suture materials: structure and absorbability

Monofilamentpolyglecaprone (Monocryl®) polydioxanone (PDS®) polyglycolate (Maxon®)steel wire polyamide (Nylon)
 polypropylene (Prolene®, surgilene®)
/chromic catgut polyglycolic acid (Dexon®) polyglactin 910 (Vicryl®)steel wire
 polyamide (Nylon) polyester (Dacron®, Mersilene®) silk

For absorbable materials, a further subdivision is made based upon the speed of absorption. A differentiation should be made between loss of tensile strength and disappearance of the material from the tissue (absorption). For all materials, the speed with which the strength decreases, exceeds that of absorption. This is clearly illustrated in Table 2, which includes the results of independent research and data from the manufacturers of commonly used veterinary suture materials.

Table 2. Absorbable material: structure, loss of strength and absorption time

NameStructure50% strength0% strength100% absorbed
Vicryl rapide®Braided5 days2 weeks42 days
Vicryl®Braided21 days1-2 months3 months
Monocryl®Monofilament7 days1 month3 months
PDS II®Monofilament>6 weeks 182 – 238 days

When choosing an appropriate suture material, besides the factors mentioned above, handleability, the knot security and the degree of tissue reaction are also of importance. Last but not least, the ease of suture removal after healing should be determined, for instance in wild(er) animals. The ideal material is easy to handle, causes little tissue reaction, has secure knots, retains its tensile strength as long as necessary, is easy to remove and rapidly dissolves afterwards. Unfortunately, there is no material that satisfies all these criteria, but recent developments have decreased the distance between the ideal and reality for certain materials. The traditional natural materials (catgut, chromic catgut and silk) are now considered obsolete for many procedures. Catgut may carry prions (BSE), which is a major argument against its use in human medicine. Stainless steel wire has a number of advantages (great strength, little tissue reaction) but is not easy to handle and therefore often less suitable for general veterinary practice. The synthetic braided non-absorbable materials are generally easy to handle but may cause a certain degree of tissue reaction and are easily colonized by micro-organisms. This may lead to suture granulomas and fistulas, which may be hard to treat and lead to a second surgery to remove the suture foreign body. In situations where the suture material remains in the body, the best option is therefore synthetic, absorbable multi-/monofilament suture material or synthetic nonabsorbable monofilament suture material. The choice of suture material is further determined by the speed of tissue recovery and the forces exerted on the sutures during healing. Non-absorbable suture material is an excellent choice for skin closure; monofilament is generally preferred over braided suture material because it has a decreased capillary function, allowing bacteria to enter the suture tract.

Suture thickness is expressed as a number, which not only indicates the diameter but also the suture strength (USP, United States Pharmacopoeia). Thickness is expressed as a whole number (strong) or with several zeroes (the more zeroes, the thinner the material). Materials with the same number may have a different diameter if they have different tensile strengths: e.g., catgut 0 is thicker than stainless steel 0. The choice of suture material size is determined by the forces exerted on the suture, which vary according to the tissues, motility of the region and species in which the material is used. In small animals, commonly used sizes are between 4-0 (intestinal sutures) and 0 (sutures in the linea alba of a large dog). In the horse and farm animals, sizes usually vary from 3-0 (intestinal suture in a foal) to 6 (linea alba of an adult horse). In specific organs, for example the eye, specific suture sizes between 5-0 and 10-0 are used. EP units (European Pharmacopoeia) are used alongside USP units. The EP unit merely indicates the thickness: 1 EP = diameter of the suture is 0.1 mm, 2 EP = 0.2 mm, 10 EP = diameter 1 mm (the largest size available). Specific suture materials

New types of suture material are being developed all the time. One of the latest advances in suture biomaterials is barbed sutures, which have gained popularity in reconstructive and endoscopic surgery (Figure 1). These self-anchoring barbed wires have barbs cut into the suture material that engage the tissue and prevent the suture from pulling out of the tissue, thus eliminating the need for a knot. These suture materials have significantly decreased surgical time (as tying knots endoscopically can be time-consuming) and are cosmetically more pleasing when used in superficial subdermal patterns. Barbed sutures have certain handling characteristics that should be recognized, however. Once the needle is pulled through the tissue and barbs engage the tissue, the suture cannot be removed by simply backing the needle out. The needle must therefore be positioned well and checked carefully before pulling the thread through the tissue. The learning curve associated with the use of this type of barbed suture material seems steeper than non-barbed materials.

Figure 1. Example of barbed suture material

5.1.3 Suture needles

Suture needles are characterized by the following features:

  1. diameter
  2. curvature
  3. suture attachment

The diameter is not identical over the entire length of the needle; the profile of the tip is generally different to that of its shaft, which is again different from that of the eye.

The main division is between round needles and cutting needles. Round needles have a round to oval shaft that tapers to a sharp point at the tip (like a sewing needle for textiles). In these needles, the shape of the needle pushes the tissue aside and the suture track matches that of the suture material, leading to a minimal risk of leakage along the suture and tearing of the tissue. However, tissue penetration is more difficult than with cutting needles, and this is especially notable at the moment of insertion. Round needles are mainly used in soft tissue and in locations where leakage via the suture path or tearing of the tissue are undesirable. Examples include suturing of the digestive tract and the bladder. Packaging for round needles has either a symbol of a circle with a dot in the middle or includes the words “taper point”.

Cutting needles also have a round or oval body, but the tips have cutting edges to improve passage. Usually there are three cutting edges, so the needle tip has a triangular profile; in the cutting needle, the tip of this triangle points inwards, and in the reverse cutting needle it points outwards. Approximately half of the length of the needle has the triangular shape; the remainder is round or oval. Since tissue is mainly compressed at the inside of the needle curvature, there is an increased risk with cutting needles that, when tightened, the material will cut deeper into the tissue than with reverse cutting needles. Needles that are supplied individually are usually cutting needles, while needles of atraumatic suture material (see below) are usually reverse cutting needles. This is depicted on packaging using a triangular symbol with the point directed downwards (reverse cutting).

The taper cut needle is an intermediate between a round and cutting needle. Most of the shaft is round but the tip is (reverse) cutting. Only a short length of the needle has the triangular shape in this model. The symbol included on packaging is a triangle (point down) in a circle. If the needle tip has more than 3 edges, it is referred to as trocar point. The needle is usually a little thicker than its round equivalent. Taper cut needles are used in tissues requiring a round needle path, but which have reasonably firm consistency, such as the canine gastric wall. A taper cut needle may also be a good choice for closing a rectal tear. The flat needle, usually with a taper point tip and made of extra-strong, black-colored material (Visi-black®) is a recent development (Figure 2).

Figure 2. Schematic representation of various needles types commonly used in surgery. A. Blunt needle; B. Taper point needle; C. Taper cut needle; D. Reversed cutting needle.

Besides these needle types, there are also a number of variants developed for specific uses, such as the spatula needle, used for sutures of the cornea. The shape of the needle is designed to create a needle path with minimal tissue trauma (see Chapter 15).

The curvature of the needle is given in eighths of a circle and varies from straight to 5/8 of a circle. Straight needles are rarely used nowadays; they are indicated for the penetration, at right angles, of a flat surface. An example is the suturing of an aural hematoma in the dog.

The curvature of the needle determines the pathway of the needle through the tissue (depth) and the angle at which the needle enters and leaves the tissue. Lightly curved (3/8) needles are used for superficial sutures in easily accessible areas (e.g., skin sutures), moderately curved (4/8) needles for tissue that is less accessible or that needs deeper sutures (e.g., perforating intestinal suture), and strongly curved (5/8) needles for tissue that is poorly accessible and requires deep sutures (e.g., closing an inguinal hernia).

In loose or detached suture needles, suture material needs to be threaded through the eye of the needle before use. This part of the needle is considerably wider than its shaft, and the suture material is also doubled up at this location, making the whole much bulkier at eye level than the diameter of the suture material itself, thus causing more trauma to the tissue (traumatic needles) than needles with suture material threaded into the needle (atraumatic needles). The large needle path created is a disadvantage, in particular in areas where leakage is undesirable, such as the intestine or the urinary bladder. The increased resistance caused by the ‘bulky eye’ leads to a stronger pull during tissue fixation and needle penetration, and thus more tissue trauma.

In atraumatic needles, the material is attached to the base of the needle during the manufacturing process. The transition from needle to suture is therefore much smoother. As the diameter at the eye level of the needle is similar to that of the thickness of the material, the needle track is narrower. As a consequence, less force is needed for needle penetration. These two effects make this type of suture more atraumatic.

5.1.4 Staples and clips

Staples are increasingly used in veterinary surgery. They are mainly used for skin closure or for suturing organs with specific stapling instruments. The major advantage of staples is their ease (and therefore speed) of use. In skin closure, stapling clearly saves time when compared to conventional suture techniques, and without loss of safety or cosmetic effect. While stapling the skin leads to an initial poorer cosmetic end result than the use of a continuous subcutaneous suture (the gold standard for skin closure), its outcome is certainly no worse than that of interrupted skin sutures.

When stapling organs (e.g., intestinal anastomosis or excision of a lung or liver lobe), some mechanical staplers carry out several actions simultaneously (Figure 3). When ‘firing’ such staplers, both segments are stapled and transected simultaneously. Mechanical staplers are expensive and only have a limited number of applications in veterinary practice. In most situations, the suturing for these applications can be carried out by hand. The exception to this is endoscopic surgery. Endoscopic staplers, designed specifically for this purpose, allow procedures to be performed within body cavities through a small incision, whereby the surgeon handles the instrument by remote manipulation (outside the body).

Figure 3. A stainless steel TA (Thoraco-Abdominal) stapler with cartridge often used for lung lobectomy

Endoscopic surgery has taken flight in human medicine and is also gaining popularity in veterinary surgery. The instruments required are expensive, and ‘remote operating’ via the screen requires special skills. The technique is therefore often reserved to more specialist surgeons, with the exception of laparoscopic spaying which is increasingly available in larger general veterinary practices as well.

Hemoclips are fasteners used to clamp off blood vessels. These clips exist in metal and absorbable material (polyglactin 910 and PDS®). Metal clips are V-shaped and are clamped around the blood vessel. The absorbable clips have a locking mechanism at the tip. Although this secures closure, absorbable clips are considerably bulkier than metal clips of the same size.

Hemoclips are placed around the blood vessel with special forceps. The size of the clip should match up with that of the blood vessel. The clip should be longer than the diameter of the (flattened) blood vessel so that the clip ends interlock well, and the locking mechanism (of the absorbable clip) engages completely free of the blood vessel. If the clips are too small, the tips may puncture the wall of the blood vessel, potentially resulting in bleeding – the opposite of what was intended by using clips in the first place.

The advantage of clips compared to ligatures is the relative ease with which blood vessels may be safely clamped in less accessible (deeply located) places. Less manipulation is needed than when ligating, although the blood vessels should be well separated from the surrounding structures for hemoclips as well. A drawback is that only relatively small blood vessels (diameter < 11 mm) can be clamped in this way.

5.2 Suture techniques

5.2.1 Introduction

An incision is often closed, by approximating the wound edges with suture techniques, to obtain healing by first intention. This generally requires exact apposition of the wound edges, which is achieved by suture techniques that are as simple and use as little suture material as possible. Sutures that are too tight or too numerous may cause ischemia of the wound edges, which may severely impair wound healing.

If a wound consists of several tissue layers, such as skin, subcutaneous tissue and muscle, each layer should be sutured separately. A wide range of suture techniques is available; the surgeon should know the pros and cons of each technique in order to make the best choice for the given situation.

There is an important difference between interrupted and continuous (or running) sutures. Interrupted sutures ensure wound closure by individual sutures. This was often considered to be the safest method in the past, as the unravelling of one single suture has no consequences for the wound closure as a whole. However, if something were to go wrong with a continuous suture (unravelling of a knot, suture breakage, tearing of tissue) this may have serious consequences as the entire suture line becomes loose. On the other hand, a well-tied knot should not become unfastened. Furthermore, the risk of spontaneous breakage of modern synthetic suture material when handled appropriately is minimal, while the risk of tissue tearing depends largely on the suture technique used (sufficient tissue taken up by the suture, not pulled too tight). Interrupted techniques may be indicated when the viability of part of the wound edge is questionable (e.g., traumatic wounds). As a drawback, interrupted sutures require more suture material to close the wound and leave more behind, mainly in the form of numerous knots. Also, tying interrupted sutures takes more time; each suture needs to be tied and cut separately.

An interrupted suture is also said to be less resistant to tension in the wound area. The pull of the independent sutures on the tissue is high, causing them to tear more easily. In continuous suture patterns, the tension is spread evenly over the entire length of the wound, leading to a lower pressure of the suture material on the tissue at the level of the perforation. This means a continuous suture tears the tissue less easily. The discussion as to whether to use interrupted or continuous sutures, for instance for the closure of the abdomen following a midline laparotomy in the dog and cat, has been going on for some time. A retrospective evaluation of more than 500 abdominal closures in dogs and cats, however, has shown that a continuous suture does not lead to an increased risk of tearing or wound dehiscence.

5.2.2    Handling needle holder, needle and suture

When placing the needle in the needle holder, three points should be observed:

  1. the position of the needle in the beak of the needle holder.
  2. the place on the needle where it is picked up.
  3. the angle the needle makes with the beak of the needle holder.

The needle is picked up close to the beak tip of the needle holder; gripping nearer the joint is more likely to damage the needle as the beak is wider and increases the risk of breakage. The needle should be picked up between the tip and the end (swage of needle). The closer the needle is grasped by the tip, the higher the chance that the tip will be damaged, making its use more cumbersome. The closer the needle is held by its swage/eye, the larger the part that will reappear after tissue penetration and the easier the needle can be picked up again. Control of the direction of the needle is more complicated the closer the needle is grasped to the end of the needle, i.e., the farther away from the tip. The farther away from the tip, the bigger is the chance that you will bend the needle during the insertion process. In soft tissue, the needle is therefore held closer to the end and in firm tissue closer to the tip.

The angle between the needle and the beak of the needle holder may vary from wide to narrow but is most commonly 90 degrees; it is also possible to turn the needle around its longitudinal axis. In this way, the needle holder only needs to be rotated along its longitudinal axis to push the needle through the tissue. At angles other than 90°, additional movement of the needle holder is necessary to make the needle move along the required needle path. These movements require extra space to maneuver, and the needle may be damaged over a large circumference. Paradoxically, the smaller the available space, the larger the tendency of the surgeon to hold the needle at a diverging angle.

The way in which the suture is fed through the eye of the separate needle depends on the type of eye. There are two types of needle eyes: closed and open (spring eye). The French eye needle is, in fact, a spring double eye; a second eye exists behind the open eye (Figure 04). In closed eye needles, the material is fed through the eye. In open eye needles, the suture material is pulled through a spring slot above the needle eye; after pulling the suture through this slot, the sides of the spring coil back into place and close the eye. By feeding the suture first through the underlying eye in a French eyed needle, extra fixation can be obtained. This enlarges the amount of suture material at the end of the needle even more and renders its passage through the tissue more difficult, thereby creating more tissue trauma. Additionally, pulling the suture through the spring can damage the suture. The part of the suture that was pulled into the spring eye should therefore not be included in the suture line to prevent suture failure.

Figure 4. Schematic representation of the various eyes of a needle. A. Rolled-end; B. Drilled-end; C. Regular eye; D. Single spring eye; E. Spring double eye.

Suture material is fed through an open (spring) eye needle as follows (right-handed method):

  • Grasp the needle with the needle holder, needle eye towards the right (the point towards you).
  • Pull the suture with your left hand along the lower leg of the needle holder towards the beak holding the needle, ensuring the suture is located under the needle.
  • Pull the suture just past the needle, then upward and sideways over the end of the needle. The right hand (holding the needle holder) keeps tension on the suture while it is pulled through the spring into the eye with the left hand.

When inserting the needle, the tissue is fixated using a tissue forceps, as close as possible to the place of needle insertion and until the needle has passed through the tissue completely.

The tip of the needle should be placed correctly at the first go. During needle insertion, a higher conical resistance must be overcome than during the rest of the passage; the position of the needle tip at insertion partially determines the resistance met (depending on the type of tissue). Insertion is easiest when the needle is inserted at right angles (perpendicular) to the skin.

The distance between the point of insertion and wound margin depends on the thickness of the layer to be sutured. The distance between insertion point and wound edge should be approximately equivalent to the thickness of the layer.

When pushing the needle through the tissue, the following general forces play a role:

  1. an insertion force, pushing the needle through the first layers to the intended depth.
  2. a driving force to push the needle parallel to the surface.
  3. a movement towards the surface of the opposite side.

This is possible, even though the needle has a rigid curve, because of the flexibility of the tissue (‘the tissue follows the curve of the needle’).

The degree of rotation depends on the shape of the needle. A 3/8 curved needle should be rotated over 135° through the tissue, a 4/8 needle over 180°. The hand position at the moment of insertion determines the ease with which the rotation can be obtained. There are two starting positions: pronation (with the back of the hand turned upward) and supination (with the palm upward). By starting in pronation, the wrist will automatically turn in the correct direction and the needle will naturally follow the correct pathway.

When passing through firm tissue, the needle should be grasped closer to the tip and must be (re)grasped again several times by placing the needle holder closer and closer to the eye of the needle; in doing so, the needle is gradually pushed through the tissue rather than pulled out using force at the tip. Grasping the needle by the tip of the needle should be avoided under all circumstances, as it will damage the tip and will render the passage of the needle more difficult during subsequent suturing.

Once the needle has been driven through the tissue up to the end of the needle, it should be pulled out at the other side. For this, the needle needs to be released and picked up again. This process of releasing the grip on the needle carries the risk that nearby structures are punctured; to avoid this, the needle should be stabilized during the ‘take-over’. This may be done in several ways:

  • extraction with the needle holder while the tissue is fixed with a forceps.
  • extraction with a forceps without fixing the tissue.
  • extraction with the use of a special fixation forceps.

When the needle holder is used for extraction, the needle is stabilized by fixing the tissue near the needle. The needle is released and picked up again by the needle holder at the other side. At extraction, the same forces come into play as with needle insertion and driving. Again, the needle holder can be held in either pronation or supination. In pronation, the wrist turns to supination with ease, making the rotating movement needed for the needle path. This movement enables pulling the needle out of the tissue without awkward twisting of the wrist. As a drawback, the needle needs to be repositioned in the needle holder before re-insertion into the tissue. Extraction of the needle in supination saves time, as the needle is in the correct position for the next suture insertion. Its disadvantage is that it is more difficult to follow the needle path, as it is awkward to further rotate the hand already in supination without excessive twisting of the elbow and shoulder.

Most needles are not curved over their entire length; at its end/eye, the needle is usually straight. As a consequence, the needle should no longer be rotated when the eye is pulled through. A continued rotating movement would make the extraction more difficult and lead to tissue damage as the eye ‘ploughs’ through the tissue. The end of the spring double eye needle in particular may cause a lot of damage with improper use.

When extracting the needle with tissue forceps, the forceps are transferred from the tissue to the needle. The needle holder will hold on to the needle until the tissue forceps have been placed at an angle of 90° to the needle. The needle is then pulled out of the tissue with the forceps, held in the left hand. Here similarly, the hand movement may start from pronation or supination. Pronation has the same advantages as described above; the disadvantage of being picked up again no longer applies.

This method requires fewer manipulations and is therefore faster but has as a disadvantage that the needle cannot be grasped well with normal surgical forceps; special suture forceps with flattened and polished inserts behind the teeth are needed. Additionally, the needles may damage finer forceps or by the force exerted on the forceps during the needle extraction.

When pulling the needle through the tissue, several factors play a role:

  1. the angle at which the suture material is pulled out of the tissue.
  2. the quantity of suture material pulled through the needle path.
  3. the roughness of the suture material.

The suture lies in the groove at the end of the needle eye; the angle at which the suture is pulled out of the tissue is equivalent to that at which the eye is pulled out of the tissue. A sharp or wide angle will cause increased ‘sawing’ effect and more trauma. The quantity of suture material pulled through the needle path depends on the type of knot used and the length of the material. A smooth monofilament suture material pulls through the suture tract with more ease and less resistance than multifilament materials.

5.2.3 The surgical knot

A knot is the entwining of two suture ends in a pattern that ensures a compact intersection allowing resistance to a certain tensile force. A single entwining is called a half hitch; a knot always consists of several half hitches. Additional half hitches may be symmetrical or not. In a knot with symmetrical half hitches, both strands participate in equal degrees to form the knot; each strand will leave the knot in opposite directions (symmetrical or square knot). In knots with asymmetrical half hitches, the hitches are formed by one single strand; the strands do not leave the knot at opposite directions. Symmetrical knots are more stable than asymmetrical knots, which are also known as ‘granny or slip knots’ (Figure 5).

Figure 5. Schematic representation of various surgical knots. A. Simple; B. Square knot; C. Surgeon’s knot; D. Slip knot or Granny

A typical surgical knot consists of three symmetrical throws, derived from the square knot. The difference with the square knot is that the suture ends of the first half hitch entwine twice rather than once. As in the square knot, surgical knots consist of three half hitches. They can either be tied with instruments or by hand. Knot tying with instruments

When tying knots with instruments, the needle holder and tissue forceps may be used. In the absence of professional assistance in the form of an operating assistant, this method is faster than tying by hand. Additionally, less suture material is used, making the method more economical.

The instrument knot is tied as follows:

  • The short end of the suture material is at the ‘far’ end of the incision; it is just long enough to be picked up by the needle holder. The long end is at the ‘near’ side.
  • The needle holder is placed in closed position upon the long end of the thread, parallel to the incision.
  • The long end of the suture is circled twice around the beak of the needle holder. The beak is opened, and the needle holder then grasps short end.
  • The first half hitch is tied by pulling with equivalent force on both ends, with the long end away from the surgeon (far side) and the short end (in the needle holder) towards the surgeon (near side). The hands should not be crossed (obscuring the view of the knot) but be pulled in parallel so that the knot is easily visible.
  • To obtain a ‘flat’ hitch, both ends need to be pulled with the same force.
  • The first half hitch should not be pulled too tightly; the wound edges should join evenly (appose) but should not come under pressure.

For the second half hitch, the position of the needle holder and movement are similar to that of the first, only inverted (mirrored).

  • The needle holder is placed in closed position at the far side of the incision, on the long end of the suture.
  • The long end is circled (intertwined) once around the beak of the needle holder. The beak is opened, and the needle holder then grasps the short end.
  • The half hitch is pulled tight by moving the long end towards the surgeon (to the near side) and the short end away from him (to the far side).
  • The second half hitch is tightened more than the first. If the first half hitch was tied correctly, this will not or hardly tighten the suture any further.

The movements for the third half hitch are identical to that of the first, the only difference being that the suture is only circled once around the needle holder beak.

  • The closed needle holder is placed on the long end of the suture, at the near side of the incision.
  • Again, the long end is circled around the beak of the needle holder.
  • The third and last half hitch is pulled tightly to prevent the knot from unravelling; the pulling force should, of course, be adjusted to the strength of the suture material (Figure 6a-zf).
Figure 6a. The needle holder is used to grab the swage (end) of the needle in the suture package.
Figure 6b. The needle is gently removed from the package. Knot tying by hand

Knots can be tied by hand in two ways: with one hand or two. Both methods have a number of variations and will be illustrated for both hands. Contrary to what might be expected, both hands are needed to tie knots with one hand. Knots are referred to as one-handed as all manipulations are carried out with the left hand (right-handed technique); the right is passive, and its only role is to keep tension on the long end of the suture. For two-handed knots, the right hand plays a greater role in the manipulation of the suture.

One-handed knots can be tied faster than two-handed knots, and this is particularly useful when the placing of sutures and the tying of knots alternate. In the two-handed knot, the force applied on both ends can be better gauged; but what is gained in precision is lost in speed. Both types of knots have their own indications. The one-handed knot is used when speed is particularly important, and precision plays a minor role (e.g., closing a skin incision); the two-handed knot is preferred when precision is essential (e.g., ligating blood vessels).

The two-handed knot is tied as follows (technique for right-handed surgeons; Figure 7a-z):

Figure 7a. The far side end (white) is held in the palm of the left hand, leaving the thumb and index free to manipulate the suture, while the near side end (purple) is held in the right hand.

Figure 7b. The left index finger and thumb are held in a pistol grip while the far side (white) suture is grasped by the other fingers. The right hand grasps the near side (purple) suture between thumb and index finger.

Figure 7c. The left hand is positioned over the incision (pistol grip), with the base of the near side (purple) suture positioned behind it.

Figure 7d. The first half hitch is started by crossing the near side (purple) suture over the far side (white) suture on the left index finger. As the right hand needs to move over a larger distance, the purple (near side) end should be a bit longer than the far side (white).

Figure 7e. The tip of the left thumb is then closed against that of the left index, forming a circle, enclosing both ends of the suture.

Figure 7f. The left wrist is rotated, moving the thumb through the suture loop so that the suture intersection slips from index finger to thumb and the finger and thumb are opened.

Figure 7g. The near side (purple) suture end (now at the far side) is positioned between the left thumb and index finger.

Figure 7h. The near side (purple) suture end (now at the far side) is grasped by closing the left thumb and index finger. The right hand releases the suture.

Figure 7i. The (purple) suture is pulled through the loop by flexing the wrist and returning the thumb and index finger back to the starting position.

Figure 7j. The right hand picks up the (purple) suture again, once it has been fed through the loop.

Figure 7k. The first half hitch is tightened, with the right hand (purple suture end) pulling away and the left hand (white suture end) towards the surgeon.

The pulling force on both ends should be balanced so that the knot does not slide horizontally and remains immediately above the incision. The suture should be tightened just enough to make the wound edges meet. Sutures that are too tight may lead to oedema and ischemia, which in the worst-case scenario, may result in necrosis of the wound edges. When tightening the sutures, the suture ends are pulled at right angles to the incision and at level with the knot. If the ends are pulled in opposite directions, there is only one resulting force acting on the tissue. This force is needed to appose the wound edges. If the ends are held higher than the knot during tightening, the tissue is submitted to a second force, pulling the wound upwards. In particular when ligating blood vessels, this may lead to the tearing of tissue in the knot or slippage.

Figure 7l. For the second half hitch, the suture ends are held as at the end of the previous step, with the near end in the left hand and the far end in the right. The left thumb is extended (thumbs-up sign).

Figure 7m. The left thumb is hooked (clockwise) under the base of the near side (white) suture.

Figure 7n. The left thumb, with the hooked suture, is brought above the incision.

Figure 7o. The far side (purple) suture end is crossed over the near side (white) end, across the left thumb. Care should be taken not to pull at this stage, as it could loosen the first half hitch.

Figure 7p. The tip of the left index finger is then opposed to the left thumb.

Figure 7q. The left index finger and thumb are closed forming a circle around the suture.

Figure 7r. The left wrist is bent, moving the left index finger through the suture loop without opening the circle.

Figure 7s. The far side (purple) end (in the right hand) is pulled between index finger and thumb of the left hand.

Figure 7t. The right hand releases the (purple) suture and the left hand closes the thumb and index finger.

Figure 7u. The left wrist returns to its original position, moving the left thumb through the (white) suture loop without releasing the suture.

Figure 7v. The (purple) suture is picked up by the right hand.

Figure 7w. The knot is gently tightened by pulling with equal strength on each suture end.

Figure 7x. While tightening the knot the right hand (purple suture) pulls towards the surgeon and the left hand (white suture) pulls away from the surgeon.

Figure 7y. The second half hitch should be tighter than the first, but not so tight that the first one closes further. The end result: a square knot.

Figure 7z. The hands are back to the original position (Figure 7b) with the left index finger and thumb in a pistol grip (white suture) and the right hand holding the purple strand.

The two-handed knot technique for left-handed surgeons is tied as follows (Figure 8a-w):

Figure 8 shows the technique for left-handed surgeons

Figure 8a. The far side end (white) is held in the palm of the right hand, while the near side end (purple) is held in the left hand.

Figure 8b. The right index finger and thumb are held in a pistol grip while the rest of the far side (white) suture is grasped by the other fingers. The left hand grasps the near side (purple) suture.

Figure 8c. The first half hitch is started by crossing the near side (purple) suture over the far side (white) suture on the right index finger. As the left hand needs to move over a larger distance, the purple (near side) end should be a bit longer than the far side (white).

Figure 8d. The tip of the right thumb is then closed against that of the right index finger, forming a circle, enclosing both ends of the suture.

Figure 8e. The right wrist is rotated, moving the thumb through the suture loop so that the suture intersection slips from index finger to thumb.

Figure 8f. The finger and thumb of the right hand are opened.

Figure 8g. The near side (purple) suture end (now at the far side) is positioned between the right thumb and index finger. The near side (purple) suture end (now at the far side) is grasped by closing the right thumb and index finger. The left hand releases the suture.

Figure 8h. The (purple) suture is pulled through the loop by flexing the wrist and returning the thumb and index finger back to the starting position.

Figure 8i. The left hand picks up the (purple) suture again, once it has been fed through the loop.

Figure 8j. The first half hitch is tightened, with the left hand (purple suture end) pulling away and the right hand (white suture end) towards the surgeon.

Figure 8k. The pulling force on both ends should be balanced so that the knot does not slide horizontally and remains immediately above the incision.

Figure 8l. For the second half hitch, the suture ends are held as at the end of the previous step, with the near end in the right hand and the far end in the left. The right thumb is extended (thumbs-up sign).

Figure 8m. The right thumb is hooked (clockwise) under the base of the near side (white) suture.

Figure 8n. The far side (purple) suture end is crossed over the near side (white) end, across the right thumb. Care should be taken not to pull at this stage, as it could loosen the first half hitch.

Figure 8o. The tip of the right index finger is then opposed to the right thumb and closed forming a circle around the suture.

Figure 8p. The right wrist is bent, moving the right index finger through the suture loop without opening the circle. The index finger and thumb are released.

Figure 8q. The far side (purple) end is positioned between index finger and thumb of the right hand.

Figure 8r. The left hand releases the (purple) suture and the right hand closes the thumb and index finger.

Figure 8s. The right wrist returns to its original position, moving the right thumb through the (white) suture loop without releasing the suture.

Figure 8t. The (purple) suture is picked up by the left hand.

Figure 8u. The knot is gently tightened by pulling with equal strength on each suture end.

Figure 8v. While tightening the knot the left hand (purple suture) pulls towards the surgeon and the right hand (white suture) pulls away from the surgeon.

Figure 8w. The second half hitch should be tighter than the first, but not so tight that the first one closes further. The end result: a square knot.

The one-handed knot technique for right-handed surgeons is tied as follows (Figure 9a-l):

Figure 9 shows the one-handed technique for right-handed surgeons

Figure 9. One-handed knot tying for right-handed surgeons

Figure 9a. The (white) upper suture end is held in the right hand and the (purple) lower suture end in the left hand.

Figure 9b. The white end is held in the palm of the right hand, leaving the thumb and index finger free to manipulate the suture. The purple end is held between thumb and index finger of the left hand. The first half hitch is made by the right hand only. The right index finger is positioned parallel to the incision (pistol grip).

Figure 9c. The purple end of the suture is crossed over the white end of the suture on the right index finger.

Figure 9d. The right index finger hooks behind the white suture.

Figure 9e. The right index finger pulls the white suture under and through the loop made by the purple suture.

Figure 9f. The strand of the white suture is now pulled through the loop of the purple suture.

Figure 9g. The purple suture end is pulled away from the surgeon by the left hand and the white suture end is pulled by the right hand towards the surgeon

Figure 9h. The second hitch is started by holding the white strand between the right index finger and thumb and hooking the suture around the little finger of the right hand. The palm of the right hand is facing the surgeon.

Figure 9i. The purple strand is positioned by the left hand parallel to the white strand over the middle finger, the ring finger and the little finger.

Figure 9j. The middle finger of the right hand hooks behind the white strand of the suture and pulls it under the purple suture end.

Figure 9k. The white strand is let go by the thumb and index finger and picked back up under the purple strand by the right hand.

Figure 9l. The square knot is tightened by pulling the white strand away from the surgeon with the right hand and the purple.

The one-handed knot technique for left-handed surgeons is tied as follows (Figure 10a-n):

Figure 10. One-handed knot tying for left-handed surgeons

Figure 10a. The (white) upper suture end is held in the left hand and the (purple) lower suture end in the right hand.

Figure 10b. The white end is held in the palm of the left hand, leaving the thumb and index finger free to manipulate the suture. The purple end is held between thumb and index finger of the right hand. The first half hitch is made by the left hand only. The right index finger is positioned parallel to the incision (pistol grip).

Figure 10c. The purple end of the suture is crossed over the white end of the suture on the left index finger.

Figure 10d. The left index finger hooks behind the white suture.

Figure 10e. The left index finger pulls the white suture under and through the loop made by the purple suture.

Figure 10f. The left hand releases the white suture strand.

Figure 10g. The white strand is picked up again by the left hand and pulled through the loop of the purple suture.

Figure 10h. The purple suture end is pulled away from the surgeon by the right hand and the white suture end is pulled by the left hand towards the surgeon.

Figure 10i. The second hitch is started by holding the white strand between the left index finger and thumb and hooking the suture around the little finger of the left hand. The palm of the left hand is facing the surgeon.

Figure 10j. The purple strand is positioned by the left hand parallel to the white strand over the middle finger, ring finger and little finger.

Figure 10k. The middle finger of the left hand hooks behind the white strand of the suture and pulls it under the purple suture end.

Figure 10l. The white strand is let go by the thumb and index finger and picked back up under the purple strand by the left hand.

Figure 10m. The knot is tightened by pulling the white strand away from the surgeon with the left hand and the purple strand towards the surgeon with the right hand.

Figure 10m. The end result: a square knot. Cutting the sutures

The cutting of sutures is a task for the operating assistant. This task can only be performed well if the surgeon allows a good view of the sutures by pulling them slightly up and towards him. Sutures are cut with ligature scissors, which have short, curved blades with rounded tips. To avoid cutting the tissue, the scissors are held with the convex side to the patient. The joint of the scissors may be supported by the free hand, this increases stability and precision of cutting.

The length at which the sutures are cut depends on the tissue and the suture material concerned. Skin sutures are left long (1 to 2 cm) to facilitate their removal; all other sutures are cut short (2 to 5 mm).

5.2.4 Interrupted suture patterns

Suture patterns are commonly divided into interrupted and continuous suture patterns and the pattern is chosen depending on the tissue and the personal preference of the surgeons. There is no significant difference between the reliability and strength between either continuous or interrupted suture patterns. Simple suture

A simple suture is made as follows:

  • The needle and attached suture are inserted from outside (skin) to inside (wound), through one wound margin and then, from inside to outside, in the opposing margin.
  • Both suture ends are pulled together and the suture is tied.

There are no set measures for the distance of the sutures to the wound edge or to each other. Both distances depend on the type and firmness of the tissue, its thickness and the tension on the wound edges. However, neither of these distances should be smaller than the thickness of the tissue layer to be sutured (Figures 11a and 11b).

Simple sutures are the most commonly used suture technique. The sutures are easy to place and lead to a good apposition of the wound edges, and therefore a good wound closure. As a rule of thumb, this technique can be used if there is no tension on the wound edges.

Insert Figure 11 a and b. Horizontal mattress suture

This suture is also referred to as a horizontal U-suture.

  • The suture starts as a simple suture.
  • After penetrating both wound edges, the needle and suture pass through both wound edges again, but in opposite order and direction.
  • The suture ends, which now lie at the same side of the wound, are tightened and tied. This results in a knot on one side of the wound and a suture loop on the other side, parallel to the wound (Figure 12).

Horizontal mattress sutures are used in particular in the case of tension on the wound edges. By using horizontal mattress sutures, the tension is spread over a larger surface. The risk of tearing is thereby reduced and smaller than with simple sutures. The tension can be further decreased by placing more sutures, as the tension is divided over their total. The sutures are tightened so that the opposite wound edges just touch each other. Postoperative swelling of the wound will ensure proper closure of the wound. If the sutures are tied too tightly, this leads to wound edge eversion and possibly to ischemia and skin necrosis. This necrosis increases the risk of sutures tearing through the tissue.

In order to ensure a good circulation of the wound edges, subsequent sutures should not be placed too close together. The distance between individual sutures should be roughly the same as the width of the ‘U’s.

Interrupted horizontal mattress sutures can be used for the closure of skin, fascia and muscles. A specific indication is the closure of abdominal hernias, such as an umbilical hernia in larger animals. If such sutures are used for the closure of a small skin wound with much tension, the risk of tearing can be reduced by feeding the suture through short lengths of latex, plastic or rubber tubing at both sides of the wound: ‘horizontal mattress suture with tubing (stent or bolster) support’.

Insert Figure 12. Vertical mattress suture

Vertical mattress sutures are used to close several tissue layers with one single suture. The theoretical advantage of this suture pattern is the possibility of removing the suture material from the deeper layers once the healing process is far enough advanced. In case of contaminated wounds, this would reduce the risk of abscesses and fistulas. However, this benefit has never been proven and it is doubtful whether it applies if modern, synthetic, absorbable suture material is used.

The suture is carried out as follows:

  • First, at a reasonable distance to the wound, both tissue layers (skin and muscle) are penetrated as with an interrupted suture.
  • Needle and suture are then passed through the tissue in opposite direction at the same level, but nearer to the wound and only through the superficial layer (skin).
  • The suture is tied (Figure 13a and 13b).

The knot is at one side of the wound and the suture loop on the other side, at right angles to the wound. The first, deep bite goes through skin and muscle while the second, superficial bite only goes through the skin. The suture is removed by cutting the suture loop and pulling at the knot. Both superficial and deep sutures are thus removed at the same time. If both tissue layers were to be sutured separately, suture material could remain in the deeper (muscle) layer for some time after removal of the superficial suture.

Insert Figure 13a and 13b

Vertical mattress sutures always lead to minor wound edge eversion, which means that the wound edges, especially of the skin, will turn a little up- and outwards. This leads to a poorer cosmetic result than with normal apposition (appositional closure) of the wound edges. Cross-stitch or cruciate suture

This suture is also known as a figure-of-eight suture and can be compared to a double interrupted suture.

  • After penetrating both wound edges as in a simple interrupted suture
  • The suture ends are not tied, but a second stitch is placed next to and in the same direction as the first.
  • Only after this second stitch are the suture ends tightened and tied (Figure 14).

The visible part of the suture looks like an ‘X’. Like mattress sutures, cross-stitch sutures can be used for closing wounds under tension as the pressure of the suture is spread over the 2 suture bites. Cross-stitch sutures, furthermore, result in a good apposition of the wound edges, since the chance of wound eversion is decreased by the sutures crossing over the wound. Scars from cross-stitches can be more obvious than those of simple interrupted sutures.

Insert Figure 14.

5.2.5 Continuous suture patterns

The obvious advantage of continuous suture patterns compared to interrupted suture patterns is the speed of closure of the wound. Continuous suture patterns depend on only 2 knots on either side of the wound length. These two knots need extra careful attention while tying to prevent suture line loosening and wound dehiscence. There are no other major advantages between the two techniques, although a continuous suture line may have less risk of sutures being too tight. Simple continuous suture pattern

  • After placing a simple interrupted suture and tying the knot, the suture is continued with the long end of the suture.
  • The wound edges are penetrated in the same manner with each stitch, i.e., from outside to inside through the first wound edge and from inside to outside in the opposing wound edge.
  • Once the wound is closed over its entire length, the suture is tied (Figure 15).

At the time of needle insertion, the already sutured part of the thread is kept relatively tight by an assistant to avoid unravelling.

The suture can be placed in two ways:

  • with the needle entry and exit points straight opposite each other.
  • with the needle entry and exit points at an angle.

In the first case, the non-visible parts of the suture are at right angles with the wound, while the externally visible parts cross the wounds at an angle of approximately 45°. In the second case, the visible parts are at straight angles with the wound and the non-visible parts at an angle of 45°. There are neither major difference nor benefit between the two techniques; preferences are a matter of taste.

The ending knot of a continuous suture is tied differently than that of an interrupted one. Once the suture is finished, the needle is inserted as near as possible to the final bite at the same side of the incision. This final stitch is not tightened completely; a loop of a length of approximately 2 cm should remain. This loop is used during knotting as the short end of the suture; the knot is tied in the same manner as with an interrupted suture.

Insert Figure 15.

This suture is easy and rapid to perform and gives a good apposition of the wound edges. This technique is generally used for the closure of wounds under normal tension, and for suturing subcutaneous tissues, muscles and fascia. It does not really matter in what direction the suture is performed, although there is a difference. When suturing from left to right, the (right-handed) surgeon has a good view of the part that is already closed, but less so of the part still to be sutured; when suturing from right to left, the opposite applies. Closure from left to right makes it easier to keep a constant distance between the sutures as the finished part of the suture is in constant view (Figure 16a-zm).

Equal spacing only applies if the wound edges are of equal length. If the wound edges are different in length, the sutures at the longer side should have a larger distance in between them than those at the shorter side to allow perfect closure. The constant adjustment that is needed is easier to achieve if the surgeon has a good view of the part still to be sutured; in this situation, it is therefore easier to work from right to left.

Insert Figure 16.

Figure 11a and 11b. Schematic drawing of a simple, interrupted suture pattern.

Figure 12. Schematic drawing of an interrupted horizontal mattress suture pattern.

Figure 13a and 13b. Schematic drawing of an interrupted vertical mattress suture pattern.

Figure 14. Schematic drawing of an interrupted cross-stitch or cruciate suture.

Figure 15. Schematic drawing of a simple continuous suture pattern.

Figure 16. A simple continuous suture pattern

Figure 16a. The suture is removed from the suture package using a needle holder

Figure 16b. The suture is grasped at the caudal part of the needle (swage) and pulled out gently from the package.

Figure 16c. The needle is then repositioned in the beak of the needle holder. The beak should grasp the needle halfway the length of the needle curve.

Figure 16d. The needle is inserted into the tissue perpendicular to the skin, approximately 5-7mm from the wound edge.

Figure 16e. The needle is advanced as described in Figure 6.

Figure 16f. A simple interrupted suture knot is tied as described in Figure 6, but only the short end of the suture is cut with the suture scissors.

Figure 16g. After placing the simple interrupted suture, the suture is continued with the long end of the suture.

Figure 16h. In this example, both wound edges are penetrated by the needle in one single movement instead of two.

Figure 16i. The needle holder is repositioned to the swage end of the needle and the needle is pushed through the tissue completely.

Figure 16j. The needle is then released and picked up near the needle point (tip) and pulled out of the tissue with a rotating (pronating) rotation of the wrist.

Figure 16k. To avoid over pronating the wrist, the needle can be re-grasped in the middle part of the needle.

Figure 16l. The needle and suture material and gently pulled out of the tissue.

Figure 16m. The entire suture is pulled through the tissue putting gentle traction on the suture line and the suture knot.

Figure 16n. The needle is inserted again (as described before).

Figure 16o. The needle is driven through the tissue.

Figure 16p. The needle is picked up on the other side.

Figure 16q. The suture is pulled taut.

Figure 16r. This procedure is repeated until the suture line covers the entire incision. To form the loop, the last bite is taken in a reversed pattern (from the same side the suture ended) to form a suture loop.

Figure 16s. The needle is pushed through the tissue in a reversed manner. This often takes an unnatural bending of the wrist (pronation).

Figure 16t. The needle is picked up at the exit side of the last needle track (i.e., opposite to the loop).

Figure 16u. The suture is pulled gently through the tissue.

Figure 16v. A small loop (with a length of approximately 2 cm) is left intact on the opposite side of the exit of the last bite.

Figure 16w. The suture knot is tied similar to the interrupted suture. The closed needle holder is held parallel to the wound on the inside of the long suture end.

Figure 16x.The long end of the suture is wound once around the closed beak of the needle holder. This procedure starts the first half hitch of the knot.

Figure 16y. The beak of the needle holder is opened, and the loop is grasped by the needle holder.

Figure 16z. One can either grasp the entire loop (as shown) or one leg of the suture loop.

Figure 16za. The loop is pulled through and pulled in the opposite direction of the long suture end.

Figure 16zb. The beak of the needle holder is opened while pulling on the loop, guaranteeing equal traction on each loop ends.

Figure 16zc. The first hitch is pulled taut.

Figure 16zd. The beak of the needle holder is removed from the loop, closed and placed parallel to the wound on the inside of the long suture end (the side facing the incision).

Figure 16ze. A close up of the beak of the needle holder positioned at the inside of the long suture end.

Figure 16 zf. The long end of the suture is wound once around the closed beak of the needle holder and the beak to grasp the loop of the suture opposite to the long end of the suture.

Figure 16zg. The beak of the needle holder is closed (this time only holding one strand of the suture loop).

Figure 16zh. The second half hitch is closed by pulling the loop to the surgeon’s side (right on picture) and the long end to the opposite side (left on picture).

Figure 16zi. Opening the beak of the needle holder will allow even tension on the loop ends and the formation of a square knot.

Figure 16zj. Pulling with even tension on the loop and on the long end of the suture will guarantee the best success and prevent forming a slipknot.

Figure 16zk. The suture knot is pulled taut.

Figure 16zl. The general advice is to at least add another 2 half hitches (4-5 half hitches in total).

Figure 16zm. Both the loop end and the long end are cut at equal distances (approximately 1-2 cm from the knot) by a suture scissors. Lock-stitch suture, continuous suture after Reverdin, or Feston suture

This suture is a modified version of the simple continuous suture. However, after every bite, the emerging needle and suture are fed through the loop of the previous stitch (Figure 17). Only then is the suture pulled taught, forming a self-locking pattern by locking the suture in the loop. If the first loop is twisted over 180° before feeding the needle and suture through, the self-locking mechanism is even stronger.

Insert Figure 17

The lock-stitch suture prevents slipping of the suture during suturing and thereby prevents loosening of the entire suture. Surgeons can use this suture pattern when there is no assistant to pull the suture taut, or whenever it is undesirable that a continuous suture loosens during suturing. The lock-stitch suture is often used in general practice for closing the skin of abdominal flank operations in cattle (Caesarean section, abomasal displacement). Continuous mattress suture

This suture, also known as the ‘zigzag’ suture, is the continuous version of the interrupted horizontal mattress suture (Figure 18). All stitches are made at right angles to the wound, and every bite goes in the opposite direction of the previous one. In the end, the visible parts of the suture run parallel to the wound, while the non-visible parts are at perpendicular angles to it. This continuous suture leads to a certain degree of wound eversion but is still used occasionally for closure of the skin, in particular in cattle.

Insert Figure 18. Continuous subcutaneous or subcuticular suture

The skin (cutis) consists of a superficial epithelial layer (epidermis) and a deeper layer of connective tissue (dermis). Underneath these layers lies loose, subcutaneous, fatty tissue. The continuous subcutaneous (or subcuticular) suture is placed just beneath the skin in the subdermal fatty tissue (Figure 19a). The skin edges are thereby appositioned so closely that it is not necessary to place separate skin sutures. The advantages of this suture are the highly cosmetic effect, the lack of need to remove the skin sutures and the avoidance of premature skin suture removal by biting or licking. This technique is more challenging for the surgeon, however, and when applied incorrectly will not give a good cosmetic result.

Insert Figure 19a

  • The suture starts with a simple knot, which is placed a little deeper than the rest of the suture in the subcutaneous tissue. The risk that the suture ends will stick out of the wound edges after skin closure is thereby reduced. This risk can be further reduced by placing the first suture inverted or ‘upside-down’ (in a deep-superficial-superficial-deep pattern). This is achieved by inserting the needle from bottom to top in one side of the wound and from top to bottom in the opposite side. If the suture is cut after tying the knot, the short end will point downwards instead of up (Figure 19b).
  • After the first stitch, the needle is inserted again in the subcutaneous tissue, but this time superficially (just below the skin).
  • The suture is continued by inserting the needle and suture in the subcutaneous tissue parallel to the wound, alternately in one and the other side (Figure 19a). The needle should pass through the tissue with ease; if a resistance is felt, the dermis/cutis layer has probably been accidentally perforated, and the needle should be repositioned in the appropriate layer.
  • When crossing to the other side, a ‘swallow-tail pattern’ is made: the stitch does not cross straight over, but the needle is inserted a little backwards of the suture exit point in the opposite side. The tension created by tightening the suture causes the suture entrance and exit points to be joined. When the cross over is straight, these points are slightly displaced and small openings are created in the suture pattern.

Insert Figure 19b

The ending of the suture is very similar to its beginning:

  • The second-but-last bite is placed superficial to deep and exist in the center of deeper submucosa of the wound.
  • The one-but-last bite is placed from deep to superficial and exits close to the tip of the wound on one side; a small loop is preserved here.
  • The last bite is then placed once again superficial to deep starting in the opposite wound edge and ending in the subcutaneous tissue next to the second-but-last suture loop. This procedure is only possible if the previous stitches/bites are not pulled too tight (Figure 19c).
  • The suture is tied, and the ends are pulled parallel to the wound, allowing the knot to slip to the deep.
  • Once the suture is tied, the loop is cut short. The needle and the long end of the suture are inserted from deep (bottom of the incision) to superficial through the skin, so that the needle emerges just cranial to the wound.
  • The suture is pulled taut and the suture is cut close to the skin, so that the cut end disappears back into the tissue.
  • Alternatively, the final knot can be tied to a long end of the subcutaneous suture

Insert Figure 19c.

The end result is a completely closed incision without suture parts sticking out. Far-near patterns

Both with interrupted and continuous sutures, the tissue bites are placed at equal distance to the wound. If the suture is used for wound closure of tissues such as fascia or muscle aponeurosis, with a certain amount of tension on the wound, there is a considerable risk that the wound will tear after suturing. In this case, not only one or several sutures will tear, but the entire wound with the suture material may tear along the insertion points of the sutures (like tearing paper along a perforated line). Placing the stitches at varying distances to the incision will prevent this type of tearing. The technique can use interrupted and continuous suture patterns.

The interrupted version of such a suture is placed according to the ‘far-near-near-far’ pattern:

  • First, the needle is inserted far to one side of the wound edge and re-emerges in the opposite side near to the wound edge.
  • In the same vertical plane, the needle is inserted again in the first wound edge, but now near to the edge, to re-emerge far in the opposite wound edge.
  • Both suture ends are tightened and tied (Figures 20a and 20b).

Insert Figure 20a and 20b.

The continuous version follows the ‘far-far-near-near’ pattern:

  • The suture starts as a normal continuous suture.
  • After tying the first knot, the suture continues by first inserting the needle far to one side of the wound edge. The wound is crossed straight and the needle re-emerges in the opposite side, far to the other side of the wound edge.
  • The wound is now crossed at an angle and the needle is reinserted near to the first wound edge and emerges on the other side near to the edge.

This pattern is continued until the suture is completed (Figure 21).

[Insert Figure 21]

5.2.6 Specific sutures for hollow organs

When suturing hollow organs, there are two important things to consider:

  • leakage should be avoided
  • the lumen should not be reduced to such a degree that it hinders the passage of the content (stenosis).

Leakage may have very serious consequences as the content of hollow organs is not sterile. This applies to the gut, but also to the diseased stomach, the urinary bladder and the gall bladder, which often may have contaminated contents.

Leakage of a suture line depends on various factors:

  • the general condition of the patient
  • the condition of the tissue
  • the suture technique used
  • the suture material of choice

The surgeon influences most of these factors.

As for the suture technique, it is important to choose between a single and a double seam. Double seams (two-layer closure) reduce the lumen to a greater extent than a single seam and are mainly used in organs with a large lumen. The size of the lumen depends on the organ and on the species concerned. A reduction of the lumen could have a particular impact if the organ concerned is small to start with, such as the intestines of a cat. A double seam in the intestines of a cat or dog leads to a substantial reduction of the lumen, but less so in the stomach. In the horse, the intestinal diameter is so large that a double seam poses no hindrance to the passage of ingesta.

A second important aspect concerns the layers that are perforated by the suture. By 1887, it had already been proven that the submucosa is the strongest layer of the intestine (“A suture of this coat is much stronger than a shred of the entire thickness of the serosa and muscularis”). The other layers (serosa, muscularis and mucosa) contribute to the strength of the seam to a much lesser extent. This has led to the basic principle that the submucosal layer should always be included in intestinal sutures. In most single-layer techniques, both the submucosa and the mucosa are included. In double-layer techniques, the submucosa is included in the first layer but not in the second.

If the mucosa is included in the single-layer technique, there is – in theory – an open connection with the lumen; in practice, the implications are questionable. The incision itself is also an open connection and will not become watertight immediately after suturing. The seam is in the beginning sealed mainly by fibrin clotting in the wound. If this fibrin seal is insufficient (e.g., patients in poor general condition), even a perfectly sutured seam may leak.

When choosing the suture material, two factors play a role: the chemical composition and the structure. In intestinal sutures, absorbable material is preferred. Regarding the structure, monofilament suture material (such as Monocryl®) is to be preferred over braided material (such as Vicryl®). Nonabsorbable braided material has the disadvantage that it may be colonized by bacteria. In an intestinal suture, this could lead to the migration of intestinal micro-organisms to the abdominal cavity. The risk is reduced when multifilament absorbable sutures are used, as these are not easily colonized. This is partly caused because the core of many of the resorbable suture materials contains a bacteriostatic concentration of polyglycolic acid released by hydrolysis.

However, in spite of this reduced risk of multifilament absorbable suture material, most surgeons will prefer monofilament absorbable suture material. The diameter of the suture also plays a role, as it determines the size of the needle path. Depending on the species, relatively thin material is chosen, ranging from 4-0 (dog, cat) to 2-0 (horse, cattle). The simple interrupted approximating technique

This is a simple interrupted suture pattern where the sutures are tightened in such a manner that the wound edges are appositioned without tension or compression. This suture is used for longitudinal incisions (e.g., enterotomy) and intestinal resections (end-to-end anastomoses). With this suture, the wound edges have a tendency to evert (eversion). Often, the mucosa of the wound edges protrudes through the sutures. If this is not corrected, the mucosa remains visible on the outside of the closed suture. This can be avoided by having an assistant pushing the mucosa back inwards during the tightening of the suture using curved artery forceps, such as mosquito forceps. In this way, a seam is created where the various layers of the intestinal wall (serosa, muscularis, mucosa) are appositioned without inversion or eversion. The protrusion of mucosa does not delay wound healing of intestines per se, so many surgeons will not perform the above-described technique.

This minimal compression technique is called an appositional (or approximating) suture technique and is considered to be the gold standard for intestinal suturing, resulting in the best anatomical reconstruction. The technique was introduced in 1974 by DeHoff and remains the most commonly used method in companion animals. The crushing technique

With this technique, the sutures are placed in the same manner as with the simple interrupted approximating sutures. However, when tying, the sutures are pulled so tightly that they ‘cut’ through both the serosa and the muscularis (Figure 22). The suture thereby only remains attached to the submucosa; the only layer involved in the suture. Poth and Gold introduced the technique in 1968 with the idea that the circulation of the intestinal wall would be less disrupted if the sutures encompassed less tissue. However, no research undertaken so far has been able to support this theory.

Insert Figure 22.

The advantages of appositional sutures are that they do not reduce the lumen size, and they allow good wound healing due to the correct anatomical reconstruction with a minimal inflammatory reaction and therefore scar tissue formation. The crushing suture is suggested to cause more inflammation than the appositional suture. When an appositional closure is chosen, the individual sutures should be placed with the utmost care to reduce the risk of leakage. The (modified) Gambee suture

The Gambee suture pattern has been used to create an appositional intestinal suture line. The advantage is that it prevents mucosa from prolapsing in between sutures and creating an approximating pattern ideal for intestinal surgery.

The Gambee suture is performed by

  • taking a bite approximately 5 mm from the cut edge of the intestine and passing through and through into the lumen.
  • The next bite is on the same side entering the lumen and exiting in the cut edge just above the mucosa.
  • The needle is now inserted directly opposite in the other cut edge and exits into the lumen of the bowel.
  • The last bite is from the lumen of the bowel through all layers on this opposite site (from where you started).
  • The suture is tied on the serosal surface (Figure 23a).

Insert Figure 23a.

The modified Gambee suture starts with the same first step, perforating all layers from serosa to lumen. The second step is that the needle is passed through the lumen of the opposite side to above the mucosa of the opposite site and immediately inserted above the mucosa of the cut edge of the first side exiting in the lumen of the first side. The last step is the penetration of the lumen of the opposite site through all layers ending on the serosal surface of the opposite site (Figure 23b). The main advantage of the modification is that it is easier and thus faster to perform.

Insert Figure 23b. The Schmieden suture pattern

The Schmieden suture is a continuous perforating suture where the needle always passes through the wound edges from the mucosa to the serosa. The suture therefore passes through all layers of, for example, the intestinal wall: mucosa-muscularis-serosa. When the suture is tightened, the mucosa of one wound edge is always pulled on top of the serosa of the opposite side (Figure 24). This prevents both wound inversion and eversion. The lumen is hardly reduced at all. The Schmieden suture can be placed easily and fast.

Insert Figure 24. The Lembert suture pattern

The Lembert suture is often used as a second layer of a double seam (double layer closure). It is a non-perforating (seromuscular) suture, which can be either interrupted (Figures 25a and 25b) or continuous (Figure 26). The suture is made as follows:

  • Starting at one wound edge, the needle is inserted in (for instance) the intestinal wall, through the serosa and muscularis into the submucosa and then back out again through the muscularis and serosa. The direction of insertion is at right angles with the wound. This means that the needle is inserted a little further from the wound edge and emerges nearer to the wound.
  • The needle is inserted in a similar way in the opposite side, starting nearer the wound edge and re-emerging a little further away.
  • The suture ends are tightened and tied.

Insert Figure 25a and 25b.

  • The suture line is continued either in an interrupted or continuous manner.

Insert Figure 26.

When tightening the sutures, the wound edges inverse (serosa against serosa) over a distance determined by the distance between the wound and the outer stitches of the suture. Wound inversion causes an internal tissue ridge that reduces the lumen. The degree of lumen reduction depends on the amount of tissue inverted. This in turn depends on the distance between the bites and the wound edge. The degree of lumen obstruction depends on the degree of inversion and the normal lumen size of the intestine.

A certain amount of inversion in the small intestine of a smaller animal (dog, cat) may have serious consequences for the passage of ingesta, while the same amount of inversion in the large intestines of a horse may have none at all. The Cushing suture pattern

The Cushing suture is a continuous, non-penetrating, and therefore seromuscular suture (Figure 27). This suture is also often used as a second layer in a double seam. The needle is passed through the intestinal wall at each stitch and, as in the Lembert suture, through the serosa and muscularis into the submucosa, and then back out again through the muscularis and serosa. However, here the stitches are placed parallel to the wound (as opposed to perpendicular in the Lembert suture) (Figure 26). After every stitch, the needle crosses to the other side for the next stitch. The Cushing suture also causes inversion of the wound edges. The closer the stitches are placed to the wound edge, the less the degree of inversion, and therefore the less the degree of lumen reduction.

Insert Figure 27. Uterine suture pattern (Utrecht method)

For the closure of an incision in the uterus (Caesarean section), a specific suture technique has been developed: the Utrecht method. The suture can be considered as a modified Cushing suture (Figure 28). It is a continuous seromuscular suture, whereby perforation of the endometrium should be avoided. If the suture is placed correctly, both wound edges are well appositioned, while there is little inversion of the wound edges.

In a Caesarean section of a cow, the suture is placed as follows:

  • Approximately 2 cm above the upper wound angle, the needle is inserted through the uterine wall (serosa – muscularis – serosa), after which it emerges some 2 cm to the left of the insertion point.
  • The needle is then inserted about 2 cm to the right of the initial point of insertion, to emerge at or near the starting point.
  • When the knot is tied, the wound edges inverse in such a way that the knot is embedded.
  • At 1.5 cm from the wound margin, the needle is then inserted into the uterine wall at an angle of 30-45° to the incision and emerges close to the wound margin. This stitch is repeated on the other side of the incision, whereby the insertion point is approximately 1/3 stitch more caudal than the exit point of the previous stitch.
  • These stitches are repeated until the lower incision point is reached.
  • The suture is closed in a similar way in which it began, so that the final knot and both wound margins are embedded.

Insert Figure 28. Single or double suture layer

The closure of incisions in the wall of the digestive tract or of an anastomosis following intestinal resection should be carried out with care. Leakage at the seam, causing non-sterile intestinal content to leak into the abdomen, may lead to septic peritonitis, with a potentially fatal outcome.

Depending on the size of the intestines, many surgeons will therefore prefer to close gastro-intestinal wounds with a double suture layer; in other words, after the first layer wound closure, a second suture line is placed on top. Often, a different suture technique is used for the second layer than for the first. This means that there are many different ways to close an incision of the digestive tract. The method used depends on the species and the part of the digestive tract concerned, which determines the diameter of the digestive tube at incision level. The personal preference of the surgeon will also play a role.

If an intestinal wall is closed in two layers, the second layer is always a non-perforating (serosa and muscular layers) and inverting suture pattern. A Lembert or Cushing suture may be used, for instance. The first layer should always include the submucosa; usually a continuous suture is chosen for its speed.

When a second (inverting) suture layer is used, the final amount of inverted tissue will be bigger than when a single non-perforating suture (one-layer closure) is used. This is because the second layer will completely invert the first suture layer. A double suture layer therefore has an even bigger impact on the local intestinal lumen than a single layer, even if they are of inverting sutures. This is why a Cushing suture is often preferred as a second layer, as this leads to less inversion than the Lembert suture. Parker-Kerr suture

After intestinal resection, the open ends of the digestive tube sometimes need to be closed. This is done, for example, when performing a side-to-side anastomosis. For the closure of the open ends, traditional suture methods may be used as well as the Parker-Kerr suture pattern specifically designed for this purpose.

  • Prior to the actual intestinal resection, the intestinal lumen is clamped at the incision site using two intestinal forceps. Different kinds of intestinal forceps may be used, but straight intestinal forceps should be placed on the part that will be preserved (closed). The intestine is transected alongside these forceps.
  • A Cushing suture is placed across the forceps without a knot at the start or end (Figure 29a). Once the suture is placed over the entire length, the forceps are carefully removed, while pushing the wound margins inward and pulling on the opposite ends of the suture. This will cause the wound edges to invert and the wound to close.
  • With the suture end containing the needle, a second suture layer is placed, either a Cushing or a Lembert suture (Figure 29b). This second suture layer will proceed in the opposite direction of the first. The suture is finished by tying the two suture ends.

Insert Picture 29a and 29b.

The Parker-Kerr suture pattern provides a good closure of the intestinal incision. During suturing, the risk of bacterial contamination from the intestinal lumen is minimal, as the intestines are kept closed and the leakage of intestinal content is avoided. Non-perforating purse-string suture

A non-perforating purse-string suture, also known as the ‘tobacco pouch suture’, is mainly used for the closure of small openings in the wall of hollow organs. These mainly concern holes caused by puncturing the organs, e.g., for the removal of excessive gas or fluid. If the puncture is carried out by a thin needle (compared to the wall thickness) at an angle (i.e., not perpendicular) to the intestinal wall, the opening will close once the needle is withdrawn. In this case, the risk of leakage is very small. However, if a relatively thick needle is used or a stab incision, it is preferable to close the puncture opening using a purse-string suture.

The suture is a continuous suture that consists of several non-perforating (sero-muscular) stitches placed in a circular manner and ends near its beginning (Figure 30). The suture is usually placed before the needle is inserted through the intestinal wall. At the same time that the needle is withdrawn, the suture ends are tightened and tied. The puncture opening is closed effectively while the wound margins will invert due to the sero-muscular stitches. No second layer is needed. In companion animals, this suture pattern is commonly used to temporarily close the anus, during perianal surgery or after a prolapse of the rectum.

5.3 References and further reading

Boothe, H.W. (2012). Instrument and Tissue Handling Techniques. In Tobias, K.M. & Johnston, S.A. (eds.), Veterinary Surgery Small Animal (St Louis: Elsevier), vol. 2, pp. 201–13).

MacPhail, C.M. (2013). Surgical instrumentation. In Fossum, T.W., Dewey, C.W., Horn, C.V. et al. (eds.), Small Animal Surgery, 4th ed. (St. Louis, Missouri: Elsevier Mosby).

Schmiedt, C.W. (2012). Suture Material, Tissue Staplers, Ligation Devices, and Closure Methods. In Tobias, K.M. & Johnston, S.A. (eds.), Veterinary Surgery Small Animal (St Louis: Elsevier), vol. 2, pp. 187–200.

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