Surgery Guidelines for Laboratory Animals

Find guidance on performing survival surgery on animals as part of a protocol approved by the Institutional Animal Care and Use Committee (IACUC).

Guidelines pertain to all species. However, special considerations may be necessary based on experimental- or species-related needs. Please consult with a Research Animal Resources (RAR) veterinarian to discuss any specific considerations prior submitting a protocol or protocol amendment for IACUC review.  

In addition, the more detailed IACUC policy on rodent survival surgery serves as a reference for developing a surgical plan in rodents.

Surgical definitions

Surgical definitions

Survival surgery: Animal recovers from the procedure and anesthesia. This surgery requires aseptic procedures, including surgical gloves, masks, sterile instruments, and aseptic technique.

Terminal, acute, or non-survival surgery: Animal is humanely euthanized while still under anesthesia. Certain principles of asepsis may not apply depending on the procedure length. View exceptions (below).

Major surgical procedure: Surgery that penetrates and exposes a body cavity or any procedure that permanently impairs physical or physiological functions (e.g., laparotomy, thoracotomy, craniotomy, amputations).

Minor surgical procedure: Surgery that does not penetrate or expose a body cavity or permanently impair physical or physiological functions (e.g., subcutaneous osmotic pump placement, skin biopsy).

Sterilize: To eliminate agents injurious to health on equipment and supplies used in aseptic surgery. Common methods include steam autoclaving, ethylene oxide gas, and cold sterilization.

Disinfect/sanitize: To make physically clean and to remove and destroy agents injurious to health, to the maximum degree that is practical.

Aseptic technique: Procedures before and during surgery to limit microbial contamination of the surgical site.

Facilities requirements

Facilities requirements

Dedicated workspace

Defined as an area within the lab that is free from unnecessary equipment and materials, easily sanitizable, and has limited traffic flow during procedures. Hood space protecting patient is optimal.

  • Species/procedures allowed: Survival surgery in mice, rats, hamsters, guinea pigs, and non-mammals; non-survival surgery in any species; and minor procedures in any species.
  • Guidance: At the time of surgery, postpone all other laboratory work.

Dedicated surgical room

Defined as a room designed for surgical procedures that maintains the appropriate environmental conditions, sanitation standards, and dedication to surgical procedures.

  • Species/procedures allowed: Mammals larger than guinea pigs undergoing a major survival procedure.
  • Guidance: Periodically clean floors, walls, and other surfaces within the room in addition to the immediate surgical area. Limit non-surgical room use to prevent contamination.

Preparation and procedures

Pre-operative preparation

Pre-operative preparation

Pre-operative considerations are an important part of planning surgical procedures. Consider four main areas when preparing a surgical procedure: Surgical space, instruments, surgeon, and animal.


Surgical space: Workspaces and surgical rooms

Disinfecting: Regardless of the type of facility or space, clean and disinfect all surfaces necessary for the surgical procedure using appropriate disinfectants (e.g., diluted bleach, hydrogen peroxide products such as Rescue, or similar products with broad disinfectant efficacy).

Traffic flow: During surgical procedures, limit traffic to the individuals necessary for the surgical procedure.  


Surgical instruments

Pre-procedure: Sanitize and sterilize all instruments prior to starting a surgical procedure.  

Storage: Date and store unused packs for up to six months. After six months, surgical packs need to be repackaged and resterilized before use.

Primary sterilization: Accomplish this through any of the following methods:

  • Pressurized steam (autoclave): This is the most common sterilization procedure for surgical instruments, and is accomplished by placing instruments in appropriate containment for autoclaving and storage. Examples include placing instruments in self-sealing autoclave pouches or stainless steel trays wrapped in surgical paper designed for autoclaving.
  • Ethylene oxide (gas sterilization): Commonly used for sensitive equipment or instruments.
  • Cold sterilization: Strictly adhere to the manufacturer’s directions for sterilization. If contact times or dilutions are not followed exactly, it may only disinfect instruments rather than sterilize them. Carefully monitor expiration dates of prepared solutions, as many are only good for short periods of time after activating. In addition, rinse all instruments with sterile water or saline immediately before use to prevent tissue toxicity. 

Reuse: Use newly sterilized instruments and materials for every animal. Refer to the IACUC policy on rodent survival surgery for exceptions regarding the reuse of instruments during serial rodent surgeries. 

Replacements: Immediately replace instruments anytime they fall outside the sterile field or become contaminated (e.g., use in intestinal surgery).


Animal

Location: Prepare animals for surgery away from the designated surgical space or room.

Hair removal: Remove hair from the surgical site and surrounding area to prevent contamination. Generally, the hairless area should be two to three times the size of the anticipated surgical field. Remove hair by using an electric clipper or depilatory cream (rodents). The best practice is to remove hair immediately prior to surgery.

Skin preparation:

  • Scrub the skin surrounding the animal’s surgical site with an appropriate disinfectant (iodine or chlorhexidine scrubs) and 70% alcohol combination. Like hand scrubbing, contact time is important. Scrub the area no less than three alternating scrubs with disinfectant and 70% alcohol. Work from clean to dirty: Scrub starting at the center of the surgical site and then slowly work toward the periphery of the surgical field, making sure not to move backwards.
  • Do not use chlorhexidine-based scrubs on or around eyes.
  • Consult your veterinarian regarding skin preparation in aquatic species.

Drapes or sterile coverings:

  • Prior to initiating surgery, place a sterile drape over the animal with access to the surgical site, unless the species or surgical procedure makes this difficult (e.g., mice).
  • Drapes may be paper, cloth, or plastic products, as long as they are sterile and allow for monitoring the patient under anesthesia.

Anesthesia and analgesia:


Surgeon

Pre-scrubbing: Prior to scrubbing, don all non-sterile surgical items including facemasks, hairnets, shoe covers, etc.

Scrubbing: Wash/scrub hands and arms thoroughly with an appropriate surgical scrub (e.g., iodine or chlorhexidine products).

  • Scrub hands for at least five minutes moving from fingertips to elbows. Scrubbing multiple times is acceptable to reach the appropriate contact time.  
  • Rinse and dry with a sterile towel prior to donning surgical attire.

Post-scrubbing: After scrubbing, don all sterile attire – including the sterile gown and sterile surgical gloves – using aseptic technique.

Surgical attire: Appropriate surgical attire includes a cap/hair cover, surgical facemask, shoe covers, and sterile gown.

  • Surgery on rodents and other small species does not always require full surgical attire. If using rodents, please refer to the IACUC policy for rodent survival surgery.
  • If aseptic technique is broken, change the affected article immediately prior to continuing with surgery (e.g., new gown or surgical glove).

Intraoperative procedures

Intraoperative procedures

Using appropriate intraoperative technique is essential for a good surgical outcome. This involves maintaining aseptic technique and conscientious tissue-handling during surgery.

Basics for a successful surgery:

1. Assessing and ensuring appropriate anesthetic depth

Prior to initiating surgery, confirm the appropriate anesthetic depth by checking the reaction to stimuli (e.g., toe pinch, palpebral reflex), body tone (e.g., jaw tone in swine), and physiologic parameters (e.g., heart rate, respiratory rate, etc.). Use multiple parameters to assess depth.

2. Aseptic technique procedure

  • Keep hands within the sterile field created by the drape or instrument tray. If you touch areas outside the sterile field or if a glove breaks, immediately change the contaminated article (e.g., gloves, gown).
  • Carefully place instruments to maintain sterility. Immediately replace contaminated instruments.
  • Keep surgical drapes clean, dry, and in place to provide appropriate protection. Keep the drape in place using towel clamps, sutures, or adhesives. Remove these carefully to prevent injury to the animal’s skin.

3. Appropriate tissue-handling

  • Limited, gentle handling of tissues is essential to prevent infection, delayed healing, and incision site dehiscence. Examples of gentle handling include using atraumatic forceps during organ manipulation and periodically wetting exposed abdominal organs.  
  • IACUC requires surgical experience. Training can be provided by an experienced lab member or through RAR.

4. Closure procedures

Appropriate suture size, type, and closure pattern are necessary to prevent dehiscence and delayed healing.  Please discuss any questions about size, type, or pattern prior to surgery with an RAR veterinarian. RAR offers a suture training class by request that covers all of these properties. Suture choice considerations:

Size: Appropriate size will vary by species and tissue. For example, skin closure in a mouse will require a 5-0 or 4-0 gauge, whereas skin closure in a dog will require a 3-0 or 2-0 gauge.

Type: Suture type is dictated by the surgical site and tissues involved. Properties of suture material include:

    • Absorption properties (absorbable vs. non-absorbable): Absorbable sutures are most commonly used within tissues, as they don’t have to be removed. Non-absorbable sutures are most commonly used in skin and are removed in 7-14 days.
    • Composition (monofilament vs. braided): Monofilament sutures are recommended for skin closure because they don’t wick bacteria. Braided sutures tend to wick bacteria and should not be used in skin or in organs where contamination may be present (e.g., intestine, bladder).

Pattern: The most commonly used suture pattern is the simple interrupted closure. It is good for tissue apposition, holds the incision closed even when a few sutures fail, and can be used for most situations. In high-tension areas (e.g., around limbs, on head), other patterns may be more suitable.  

Decrease potential dead space by suturing tissues layers while closing. If space is left between tissues, it can fill with fluid or blood, leading to impaired healing, infection, and/or abscesses. Alternatively, if tacking down tissues with sutures is impossible, use a drain to limit fluid accumulation during the healing process.

Skin closures are difficult in animals as they tend to chew or lick at the closure sites. Your veterinarian may recommend using intradermal sutures, surgical glue, or metal clips instead of or in addition to regular sutures. If skin closures dehisce, immediately contact the area veterinarian to determine appropriate treatment steps.

Anesthetic recovery and post-operative procedures

Anesthetic recovery and post-operative procedures

Post-operative monitoring and care must be performed per the IACUC’s policy on anesthesia, surgery, and post-procedural recordkeeping, which can be found on the IACUC’s Animal Use and Guidelines & Exceptions webpage

In addition, address the following post-procedural care items in the surgical description:

1. Anesthetic recovery

  • Upon completing the surgical procedure, monitor animals during recovery from the anesthetic event. This is a critical time; careful monitoring may prevent unintended complications.  
  • Provide appropriate recovery conditions including a warm environment free from objects that could cause harm. For example, use paper towels instead of corn cob bedding when recovering rodents, and remove large toys or water bowls from large animal pens.
  • Record recovery notes and stay with the animal until it is fully ambulatory and able to reach food and water. 

2. Analgesia

Provide post-procedure analgesia per the IACUC-approved protocol. Consult with your area veterinarian if animals show signs of unrelieved pain after receiving analgesics. View recommended analgesics, doses, and guidelines.

3. Surgical site monitoring and suture/staple removal

  • Observe and record the animal’s post-operative health and surgical site for a minimum of three days per the IACUC procedure recordkeeping policy. This is only the required minimum; post-surgical monitoring may be needed for longer time periods in more severe surgical cases or if complication arise.
  • Remove sutures or wound clips from the skin 7-14 days after surgery. Veterinary staff recommend that sutures in large species stay in for >10 days. Record the date of suture or staple removal in the animal’s health record. This is often the last health record entry for animals that have otherwise healed from their procedure.

Acute or non-survival surgery exceptions

Acute or non-survival surgery exceptions

Following are requirements for personnel conducting non-survival surgery at the University of Minnesota.

Guidelines are intended for appropriately trained personnel (listed on an IACUC-approved animal protocol) who will be performing approved non-survival surgical procedures.  

In some non-survival protocols, aseptic technique may still be necessary to produce the best experimental outcome (e.g., extended anesthetic times, tissue collection for transplant) and consideration should be given to each situation.  Please contact an RAR veterinarian to discuss your specific situation before determining the best surgical procedures to follow.  

In addition to these guidelines, please refer to the IACUC policy on using expired drugs or materials when developing protocol plans.

1. Instrument and equipment preparation

  • Visibly clean instruments are required at the beginning of surgery.
  • Expired surgical materials (e.g., sutures, bandage material, surgical gloves, catheters) are allowed during the procedure.

2. Medications

  • It is never acceptable to use outdated anesthetics, analgesics, euthanasia agents, or emergency drugs on any animal.
  • Examples of acceptable expired materials for use in non-survival surgery include IV fluid solutions and non-emergency drugs such as diuretics, contrast material, and antibiotics.
  • Clearly and individually label and identify each expired material. It is best to locate all expired materials in the same area – physically away from other materials or drugs – and label materials as, “Expired – for acute use only”. Use a designated storage area (e.g., cabinet or plastic bin) for expired materials and also label it as, “Expired – for acute use only”.

3. Surgery location

  • Keep the preparation area separate from the surgical area.
  • Minimize traffic flow through the surgical area.
  • Use non-porous, easily sanitized work surfaces.
  • Keep the surgery area free of all equipment and materials not necessary for the procedure.

4. Surgeon preparation

It is acceptable to wear procedure or surgical gloves.

5. Animal preparation

  • At a minimum, clip the surgical site and remove loose hair and visible dirt/debris.
  • For non-survival procedures of extended duration, attention to aseptic technique may be more important to ensure stability of the model and a successful outcome.