Best Practices for Rodent Survival Surgery

The IACUC policy for Rodent Survival Surgery detailing the Institutional and Regulatory requirements should be reviewed prior to performing surgery on rodents.

Record Keeping

Investigators are responsible for maintaining accurate records of anesthesia, surgery, and post-operative care (including analgesic administration). Information may be noted on the cage card or within a lab notebook.  Surgery and post-operative records are also available for download. These specific forms are examples only; there is no requirement that they be used.

Anesthesia/Analgesia

The selection of an anesthetic regimen is based on the type of procedure to be performed, species of animal, compatibility with the experimental design and availability of appropriate equipment/facilities. Pain adversely impacts the welfare of animals and if not controlled, is a variable that can confound the interpretation of experimental results. Anesthesia provides a loss of feeling or pain during surgical procedure but does not provide residual pain relief.  Analgesic medication must be provided to animals that are likely to experience post procedural pain. The withholding of analgesic agents must be approved by the IACUC. Veterinary consultation regarding anesthesia and analgesia selection is available at all times and all agents must be listed in your IACUC protocol.

Pre-Surgical Animal Evaluation

An animal should be healthy and acclimated to its environment to be considered an acceptable surgical candidate. Overly stressed and/or unhealthy animals make poor surgical subjects and are more likely to develop anesthetic or post-surgical complications. It is recommended that all rodents to be used in survival surgical procedures be allowed a minimum 48-hour acclimation period after shipping prior to surgery.

Note: Food and water withholding is not necessary in rodents because they cannot vomit.

Aseptic Technique

Aseptic technique refers to methods used to reduce microbial contamination to the lowest possible practical level. No procedure, piece of equipment, or germicide alone can achieve that objective as it requires the input and cooperation of everyone who enters the surgery area. This technique includes preparation of the patient and surgeon, sterilization of the instruments, supplies, and implanted materials, and the use of intraoperative techniques to reduce the likelihood of infection.

Preparation of the Surgical Environment

The area used should be made of a nonporous material that may be easily cleaned and disinfected. The area should also be away from windows, fans, air vents, and traffic, since these may introduce dust or other contaminants into the surgical area.

Preparation of the Surgical Equipment

Only sterile solutions are to be used for injectable anesthetics, fluids, or analgesics. Many supplies such as surgical suture, gloves, catheters, and syringes, are commercially available in sterilized packs; however, it is generally necessary to arrange for the sterilization of surgical instruments, drapes, and other equipment. For additional details, see Disinfectant and Sterilization Recommendations. All sterile instruments and equipment should be placed on a sterile surface, such as a drape. This provides a sterile workspace for the surgeon.

Preparation of the Surgeon

The surgeon must wear a surgical face mask, and a clean surgical gown, scrub top, or lab coat for all rodent surgeries. Before donning gloves, the surgeon should wash his/her hands. Sterile gloves or standard latex/nitrile gloves can be used. If standard gloves are to be used they must be disinfected using Sporklenz prior to starting surgery, after touching a non-sterile surface, and in-between surgeries. Allow 3-5 minutes for gloves to dry before use or wipe-down with a sterile surgical towel. *1

Preparation of the Animal

An ophthalmic lubricant (e.g. Puralube®) should be applied to the animal’s eyes after sedation to prevent drying of the cornea. Hair should be removed from at least 1 cm on all sides of the intended surgical site. Note that a separate area should be designated for surgical preparation so as to prevent contamination of the surgical area with hair. Hair may be removed with electric clippers, a razor, or depilatory cream. When scrubbing the surgical site, begin at the center of the site and circle out toward the periphery.  It is recommended that a cotton-tipped applicator is used for this process to avoid excessively wetting the animal. Draping is recommended for invasive procedures.  In small rodents a surgical drape can be made from sterile gauze pads or cut pieces of a sterile blue towel/surgical drape.

Intra-operative Animal Care

Hypothermia is the most common complication in rodent surgery. To prevent hypothermia, the animal should be laid on an insulated material, such as a clean surgical towel, for surgery preparation, surgery, and recovery. A circulating warm water or microwavable heating pad can be used underneath the towel or drape to provide heat support. Do not use electric heating pads on animals during surgery because of their irregular heating and potential to cause thermal burns to the animals.

Anesthetic depth of the animal during surgery must be closely monitored. A general indicator of adequate anesthesia is the animal’s lack of response to painful stimuli. To test whether a rodent is still responsive to pain, one can pinch the toe/foot and watch for a response. It is recommended to measure temperature and heart-rate in rodents, but at a minimum, respirations (chest cavity excursions) should be closely monitored.

Wound Closure Materials

Suture, stainless steel wound clips and skin glue are the most common wound closure material used in rodents. Wound clips are used in the skin only and must be removed with the appropriate instrument once the incision has healed. Skin glue can be used for non-tension bearing incisions.

If you are unfamiliar with wound closure and suture materials, please review the Wound Closure Guidelines and Recommendations Rodent Surgical Incisions_Closure Guidelines and Recommendations

Post-Operative Animal Care

Rodents recovering from anesthesia should not be placed in cages with alert and mobile animals, since they may cannibalize non-responsive cage-mates. If all members of a cage have been anesthetized, they may be housed together while recovering as long as they are monitored closely.

Loose bedding should be covered (e.g. with a drape or paper towel) or removed from the cage until animals are fully recovered to prevent suffocation or aspiration of bedding.

If the period of anesthesia is >20min, the animal(s) should be kept warm during recovery. A microwavable heating pad may be placed under a portion of the recovery cage such that the animal can rest either over the heated portion or unheated portion. Heat lamps are discouraged because they heat the entire cage and make it difficult for the animals to escape the heat if they become too hot.

If blood loss or hypothermia is suspected, warmed (~37 degrees Celsius) sterile 0.9% NaCl may be administered subcutaneously or intra-peritoneally before, during, or after the surgery.

Post-operative analgesics are recommended for all animals undergoing surgery, unless contraindicated by the approved protocol. For recommendations see Rodent Anesthetics, Analgesics Recommendations (this guideline is currently in development, contact the ULAR Vets for specific information).

Following surgery, a laboratory member should observe animals daily until the sutures or wound clips are removed. All skin sutures and wound clips should be removed between 10-14 days. Sutures that are not removed serve as a nidus for infection. Daily observations should be recorded. A purple cage card can be used to document these daily observations. Important post-surgical clinical signs that warrant intervention include:

  • Incisions that are red, swollen and/or have a discharge or odor
  • Animals showing a hunched posture, dehydration, labored breathing, decreased activity, rough hair coat, porphyrin staining, or weight-loss

Upon observing signs of pain or discomfort in an animal, analgesic dosing and administration should be adjusted to relieve and minimize pain if included in the approved IACUC protocol or a ULAR veterinarian should be contacted for assistance.

Multiple Rodent Surgeries

Multiple rodent surgeries or “batch” surgeries are an efficient way to perform identical surgeries on multiple rodents while optimizing supplies and time. The same set of instruments can be used on multiple animals of the same health status as long as care is taken to maintain the sterility of the instruments and the surgeon’s hands. Any part of the instrument that has come in contact with the animal should be cleaned of organic material using 70% isopropyl alcohol, sterile water or saline and sterilized via glass bead sterilization. Alternatively, instruments can be soaked in 70% isopropyl alcohol between surgeries once organic material has been removed.  In general, instruments should not be used on more than five animals before re-sterilization must be performed. The surgeon should change gloves or wipe gloves with alcohol between animals.

For further information

References

1. Performance analysis of exam gloves used for aseptic rodent surgery