This article is from the Mar.-June 1993 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M.

This issue will break from the series on Mouse Viruses, which will continue at a later date. This information is intended for use by your veterinarian; I do not recommend anyone performing anesthesia on their own pets. This information is current and comes from a chapter written by a veterinarian at U. C. Davis on anesthesia for laboratory animals. The entire chapter comes close to 100 pages and included information for anesthesia on rabbits, hamsters, and guinea pigs.

Anesthesia for Rats and Mice:

All drug doses given are in mg/kg body weight unless otherwise specified.

There have been numerous techniques developed for anesthesia in rodents. Because of their small size, endotracheal intubation and access to peripheral blood vessels is challenging. In addition, their small size predisposes them to hypothermia while anesthetized. Often there is a varied response to the various agents due to species, strain, and sex differences. When ketamine or phenobarbital is used in rats, females sleep longer than males. In mice given pentobarbital, males may sleep longer than females. For the veterinarian inexperienced with anesthesia in rodents, it is helpful to review a proposed anesthetic regimen in a few animals before attempting it on a client's pet.

Rats and mice should be free of respiratory disease and in overall good health before being anesthetized for surgery. Where available, gas anesthesia tends to have far fewer complications. For more accurate dosing in these smaller patients, it is often helpful to dilute injectable drugs 1:10 with physiological saline or sterile water. Small 25 or 27 gauge needles are preferred for injection in rodents. Rodents are not routinely fasted prior to anesthesia since these animals do not vomit.

Because of their small size, injection sites are limited. Subcutaneous injections can be given over the neck and shoulders. Intramuscular injections can be given in small volumes in the quadriceps along the front of the thigh. Intraperitoneal injections are commonly used in rodents. The animal should be carefully restrained with the head tilted down and the tail up. This allows the abdominal contents to fall toward the diaphragm. The injection is made in the caudal ventral abdomen away from the midline in order to avoid the bladder. Always aspirate the syringe for urine, bowel contents, or blood. If anything is aspirated, withdraw the needle and replace it with a new one and make another attempt in a new location. The use of IP injections may be associated with variable onset, uptake, and duration, especially in experienced hands.

Inhalant anesthesia is one of the more safe routes of anesthesia in rodents. Prior tranquilization is not required, but premedication with atropine may be used to decrease oral and respiratory secretions during induction. Anesthetic induction can be achieved by putting the patient in an induction chamber used for cats and delivering the volatile agent in oxygen. A large dog anesthesia mask for rats and a cat anesthesia mask for mice can suffice where a cat induction chamber is not available. The patient is carefully observed and removed as soon as it is adequately anesthetized.

The patient can be intubated with a small 1.5–2.5 mm Cole or straight endotracheal tube or maintained with a mask. The endotracheal tube selected for use should be cut so that the adapter is close to the tip of the animal’s nose and a pediatric adapter used to minimize dead space. Masks suitable for mice and rats can be made from the open end of a syringe case and latex exam glove to fit over the animals nose/mouth. A Bain or Ayer’s T-tube may be adapted for use in rodents. Some veterinary supply companies have commercially available anesthetic machines and ventilators designed for use in rodents and birds.

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