Guidelines for Rodent Survival Surgery
(Material adapted from the University
of Iowa Animal Care Unit and
Rodents include the following species: mice, rats, Guinea pigs,
hamster, and gerbils. Rabbits and most other species, except
amphibians and fish, must have major survival surgery performed in
an approved aseptic surgery suite. If you have questions,
concerning this policy, please call the Office of Campus
Post-operative infections in rodents can and do occur. The
misconception that rodents have an innate resistance to bacterial
infection has not been scientifically substantiated. Such
infections which may not be apparent on casual observation, will
cause loss of vessel cannulations
26, and numerous changes in physiologic
27. In accordance with good scientific practice
and standards set forth in the Public Health Service Guide for
the Care and use of Laboratory Animals and the Federal Animal
Welfare Act, aseptic surgical procedures must be used.
A separate room used primarily for aseptic procedures is
desirable; however, it is appropriate to perform survival rodent
surgical procedures in a conventional laboratory setting using
aseptic technique. The following standards for aseptic procedures
should be adopted by the investigator.
- A clean, uncluttered work area and a sanitized work surface
should be utilized for the surgery area. The work area should be
located to minimize laboratory traffic not related to the surgical
procedure and dedicated exclusively for surgery, when in use.
Considerations should also be given to locate the surgery away from
potential sources of contamination such as open windows, fans, or
fume hoods which can blow dust into the area and increase
desiccation of exposed tissues. The surgery surface should be
disinfected (70% alcohol or a quaternary ammonium compound) before
use. It often simplifies the maintenance of asepsis if a sterile
drape is then applied over the surgery surface.
- Animal preparation includes preparation of the surgical site by
clipping of the hair using a #40 clipper blade and disinfection of
the skin. Plucking of the hair may be appropriate for mice and
similarly sized rodents. Application and removal of an adhesive pad
will often remove any extraneous loose hair from the surgical site.
Disinfection can be achieved by using surgical iodine solution.
Sterile cotton pledgets or swabs dipped in disinfectant should be
applied to the incision site and applied (if possible) in a
circular fashion proceeding from the incision site to the edge of
the clipped area. The used pledget or swab should then be
discarded. After reaching the hair the pledget should not be
reapplied to the incision site since it has been contaminated. This
process should be performed a minimum of three times and the
disinfectant should be in contact with the skin for a minimum of
three minutes before the initial incision. Do not saturate other
areas of the body with disinfectant since this enhances hypothermia
which is a common postoperative complication in rodents.
- The use of sterile instruments, supplies, and wound closure
materials (suture, wound clamps)is required. Instruments used in
pediatric or ophthalmic surgery are sized appropriately for rodent
28. These tend to be delicate instruments and the
user should examine them prior to each sterilization to insure
- Draping the animal with sterile drapes to avoid contamination
of the incision, instruments and supplies is strongly recommended.
Opaque and non-opaque materials have been utilized. Clear materials
have the advantage of allowing the investigator to monitor
respirations and perfusion through the drape. Autoclavable plastic
and sterile adhesive dressings are available for use.
- Surgeon preparation: Surgical scrub of the surgeon hands
utilizing the appropriate disinfectant; use of sterile gloves and
wearing a surgical mask by the surgeon and any assistants working
in the immediate area.
The small size of rodents precludes the use of several methods
to evaluate anesthesia commonly used in larger species. However,
periodic observation of respiration, color of mucous membranes and
loss of reflected eye color (in albino animals) will provide the
surgeon with a good assessment of the animal's status. Except for
Guinea pigs, the absence of the pedal reflex is a good indication
that a surgical plane of anesthesia has been attained in rodents.
The absence of the pinna reflex is a good indicator in Guinea
Preoperative Considerations and Care:
A healthy rodent is a prerequisite to a successful surgery.
Rodents undergoing clinical or subclinical disease often experience
anesthetic complications and are not good candidates for a
successful procedure. It is recommended that animals purchased for
surgery be barrier housed prior to surgery to insure the absence of
rodent diseases. Also, in general, a minimum of 48 hours is
required for an animal to recover from the stress of shipping;
therefore, surgery should not be performed immediately upon
Preoperative Withholding of Food:
While it is common in larger specie to withhold food prior to
surgery to prevent the possibility of aspiration pneumonia after
regurgitation this practice is not necessary in rodents. Fasting
for four hours before surgery, however, my promote the absorption
of intraperitoneally administered anesthetics
29. Water should never be withheld.
To decrease tracheobronchial secretions, which may cause
obstruction of the trachea, atropine or glycopyrrolate should be
considered. Also, the investigator should be prepared to aspirate
secretions from the trachea if necessary.
Pre- and Postoperative Antibiotics:
If proper aseptic technique is utilized antibiotics should not
be necessary. In fact, antibiotics are contraindicated in hamsters
and Guinea pigs due to the frequent development of fatal
Clostridial enteritis. If the interior of the intestinal tract is
exposed, however, antibiotics are commonly administered. To have
the desired effect, antibiotics should be administered prior to
surgery to provide adequate blood/tissue levels at the time of
After surgery the animal should be placed back in a cage that is
lined with an absorbent pad. Animal bedding should not be present
since the unconscious animal may aspirate bedding into the nares
thereby compromising respiration.
The most common complication that occurs during and after
surgery is the development of hypothermia. This is often
exacerbated by performing surgery directly on a heat conducting
surface (stainless steel). This can be avoided by using sterile
pads under the animal or utilizing a circulating water pad.
Electrical heating pads cannot be appropriately regulated and
should never be utilized as a heat source. Many procedures entail
the loss of body fluids either through bleeding or drying during
surgery. In those cases the administration of warmed sterile saline
either subcutaneously or intraperitoneally will hasten the animal's
The surgical site should be monitored daily to insure that the
surgical wound is healing properly and that stitch abscesses,
dehiscence or other complications have not occurred. Usually in
seven to ten days the sutures can be removed from a properly healed
Analgesics should be administered during
surgery or immediately postoperatively. For minor procedures it may
be appropriate to administer only one dose of an analgesic. For
major procedures narcotic analgesics should be administered for the
first 24 hours postoperatively and continued if necessary. A
table of anesthetic and analgesic doses is available for
Considerations when Performing Serial Surgeries:
It is often necessary to surgically prepare several different
animals during one session using one sterile pack. This is
appropriate, providing care is taken to maintain sterility of the
instruments. The following considerations should be made:
- It may be appropriate to segregate instruments based on
potential for contamination. For example, the instruments used to
incise the skin could be dedicated solely for that purpose and
separate instruments utilized to manipulate exposed tissues and
- Manipulate the tissues with only the tips of the instruments
and avoid handling the tissues directly with your hands, which tend
to be more easily contaminated. Using a dry bead sterilizer to
resterilize the tips of instruments between surgeries will further
insure adequate aseptic technique if precautions are taken to allow
cooling of the instruments before reuse.
- Consider using a separate sterile pack for no more than four
Sterilization of Instruments and Supplies for Aseptic Surgical
Survival surgical procedures on all mammalian species must be
conducted using aseptic technique which requires the use of sterile
instruments and supplies. Many supplies such as gloves, surgical
blades, and suture materials are commercially available as sterile
packs. However, it is frequently necessary to sterilize, in house,
items such as surgical instruments, drapes, gowns, etc.
In considering methods for sterilization procedures, it is
important to differentiate between sterilization and disinfection.
Sterilization kills all viable microorganisms while disinfection
only reduces the number of viable microorganisms. High level
disinfection will not kill the more resistant bacterial spores.
Commonly used disinfectants such as alcohol, iodophors, quaternary
ammonium and phenolic compounds are not effective sterilants and,
therefore, are not acceptable for use on items intended to be used
in survival surgical procedures.
The preferred methods of sterilization are high
pressure/temperature (in autoclaves) and dry heat for items that
can withstand high temperature and ethylene oxide gas for items
that cannot withstand high temperature. However, cold chemical
sterilants may be used effectively for many items.
The following are approved sterilization procedures:
- High pressure/temperature steam sterilization using an
autoclave and appropriate monitoring systems to assure
- High temperature dry heat systems. Since it is difficult to
drape instruments prepared in this fashion they cannot be stored
for future use. Typically instruments are sterilized and allowed to
cool immediately prior to use by the surgeon.
- Gas sterilization with ethylene oxide using an appropriate gas
sterilizer and appropriate monitoring systems to assure sterility
and personnel safety.
- Cold (chemical) sterilization:
Effective and proper use of cold sterilization is dependent on
many factors including:
- The use of chemicals classified as "sterilants". Those
classified only as disinfectants (70% alcohol) are not
- The physical properties of the items being sterilized:
instruments must be relatively smooth, impervious to moisture, and
be of a shape that permits all surfaces to be exposed to the
sterilant. Instruments tend to degrade when exposed to sterilants
requiring that their integrity be assured prior to use.
All surfaces, both interior and exterior, must be exposed to the
sterilant. Tubing must be completely filled and the materials to be
sterilized must be clean and arranged in the sterilant to assure
The items being sterilized must be exposed to the sterilant for
the prescribed period of time.
- Use of fresh solutions. The sterilant solution must be clean
and fresh. Most sterilants come in solutions consisting of two
parts that when added together form what is referred to as an
"activated" solution. The shelf life of activated solutions is
indicated on the instructions for commercial products.
- Rinsing chemically sterilized items. Instruments, implants, and
tubing (both inside and out) should be rinsed with sterile saline
or sterile water prior to use to avoid tissue damage.
There are several acceptable commercial sterilants available.
Only products classified as sterilants are to be used for
sterilizing instruments and implants for surgery and they must be
used according to the manufacturer's recommendations for
Following are examples of commercial products:
Many hours required for sterilization. Corrosive and
irritating. Consult safety representative on proper use.
Glutaraldehyde is less irritating and corrosive than formaldehyde.
Must be freshly made. Must be thoroughly rinced from instruments
using sterile distilled water before use.
Chlorine dioxide (Clidox®, Alcide®)
A minimum of 6 hours required for sterilization. Presence
of organic matter reduces activity. Must be freshly made. Must be
thoroughly rinced from instruments using sterile distilled water
Discretion is required in using these agents to assure that they
are used with appropriate safety precautions and that they are
compatible with the items being sterilized. The use of
sterilization procedures other than those listed must be approved
by the IACUC.