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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 Veterinarian, 909-787-6332.
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
cannulations26, and numerous changes in physiologic parameters27. 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
surgery28. These tend to be delicate instruments and the user should examine them
prior to each sterilization to insure their integrity.
- 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 pigs.
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 arrival.
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 anesthetics29.
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.
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 surgery.
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 recovery.
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 incision.
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 review.
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 organs.
- 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
animals.
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 sterility.
- 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 adequate.
- 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.
- Exposure:
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 total
immersion.
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 sterilization.
Following are examples of commercial products:
|
Aldlehydes |
Glutaraldehyde
Formaldehyde(6% sol) |
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 |
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 before use. |
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.
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