1. Park, C.M., K.E. Clegg, C.J. Harvey-Clark, and M.J. Hollenburg. “Improved Techniques for Successful Neonatal Rat Surgery.” 1992 Lab. Anim. Sci. 1992;41:508-513.
Park et al . required a safe, controllable method of anesthesia that would allow for complicated, lengthy (30 to 45 minutes) eye surgery on day-old rat pups. They investigated two anesthesia methods intending to surmount the following two primary challenges associated with surgery in neonates:
- Mortality due to anesthesia
- Postoperative mortality due to cannibalism or neglect
Anesthesia methods evaluated:
- Halothane administered via gas anesthetic machine, permitting precise regulation of anesthetic depth for each animal
- Innovar-Vet, a neuroleptanalgesic drug combination, administered by injection via fine-gauge insulin syringe, and followed by rapid recovery via administration of Narcan, a potent narcotic antagonist
- Pregnant females were conditioned for 7-10 days before parturition by slow, gentle stroking of each animal in its cage with vocal reassurance for 5-minute intervals every 4 hours throughout the day
- Pregnant females were housed individually in large cages with a thick layer of bedding
- Pregnant rats were familiarized with the odor of agents used during surgery and postsurgically
- All incisions were carefully cleaned of blood to avoid excessive licking and were sealed with tissue adhesive
- Pups were returned to their cages after surgery until motor activity and the ability to vocalize returned
Summary of Important Techniques
- Conditioning of pregnant females to handling & key olfactory stimuli
- Housing of animals in uncrowded conditions
- Proper oxygenation of pups during anesthesia
- Careful visual monitoring during anesthesia
- Maintaining pups’ body temperatures during surgery & recovery
- Using aseptic technique during surgery
- Sealing incisions with tissue adhesive
- Allowing pups to recover from anesthesia before being reunited with dam
- Tattooing pups instead of tagging them to avoid rejection by dam
- Of unoperated pups, 7 of 8 (88%) survived anesthesia; one died of respiratory arrest
- 7 surviving pups appeared healthy and normal when examined days later
- All 63 pups subjected to eye surgery under halothane anesthesia survived
- 7 days later, 97% of remaining pups (those not euthanized) had survived and were apparently normal and healthy
- All animals (n=16) treated with Innovar-Vet survived anesthesia
- 7 days later, all pups appeared healthy and normal
2. Flecknell, P.A., Laboratory Animal Anesthesia: An introduction for research workers and technicians. 1987. London: Academic Press.
- It is essential to maintain body temperature
- Maintain good ventilation and fluid balance
- Use inhalational anesthetics so recovery is rapid and normal feeding is resumed as soon as possible. (Methoxyflurane is safe and effective.)
- **It is unclear whether induced hypothermia actually produces anesthesia or simply immobility. It’s best to use volatile anesthetics until the humaneness of hypothermia is verified.**
3. Waynforth, H.B. and P.A. Flecknell, Experimental and Surgical Technique in the Rat. 1984. London: Academic Press.
- Before and after surgery or injection, neonatal rats and the hands of the investigator should be rubbed gently with cage bedding material or urine from the mother; this will disguise the smell of the investigator and avoid possible cannibalism
- Alternative possibility: sedate mother before removing young (e.g., with 1 mg/kg i.p. diazepam)
4. Recognition and Alleviation of Pain and Distress in Laboratory Animals, Committee on Pain and Distress in Laboratory Animals. Washington D.C.: National Academy Press. 1992.
- Consider use of inhaled anesthetic whenever possible, because biotransformation is not required for its elimination and depth of anesthesia can be readily controlled
- Hypothermia may be applicable on neonates that have not yet developed effective thermoregulatory mechanisms; it has a wide margin of safety and appears effective in surgery. It is also useful as adjunct to general anesthesia in cold-blooded animals.
NOTE: As mentioned in an earlier reference, the usefulness of induced hypothermia as a viable, humane method of anesthesia has not been firmly established.
5. Rich, S., C. Grimm, K. Wong, and L. Cesar, 1990. “Gas Anesthesia Setup for Methoxyflurane Use in Small Rodents.” 32(1):7.
- Can provide a relatively rapid induction (1-5 minutes)
- Animals can be induced smoothly with no physical restraint, and recovery is quick
- See article for description of exact setup procedure
General Facts of Methoxyflurane (Metofane)
- Compatible with commonly used preanesthetic and other anesthetic agents
- Should be used with caution in animals with liver disease and toxemia
- Clinical signs are not as well defined as with other inhalation agents
- Pedal and palpebral signs are abolished early, so are not good indicators of the depth of anesthesia
- The depth of anesthesia is judged by the degree of muscle relaxation, the presence or absence of the swallowing reflex, and if the breathing is not controlled, and by the rate and character of breathing
- Causes depression of newborn. To minimize depression, the animal should be induced with the minimal amount of ultra short-acting barbiturate necessary for intubation, should be maintained with methoxyflurane in as light a plane as possible, and surgery should be completed as quickly as possible
- If depression does occur, the administration of oxygen will usually bring prompt recovery