Anesthesia is the controllable and reversible loss of consciousness induced by chemical intoxication of the central nervous system. The goal of anesthetic administration is to prevent the perception of painful stimuli without undue depression of physiological functions.
The administration of anesthesia is a part of most protocols for laboratories performing surgeries in controlled studies with mice and rats.
Characteristic features of the anesthetic state include lowered sensitivity to outside stimuli (including pain), relaxation, and diminished motor response.
For mice and rats, as with most subjects, the safest anesthetics are inhalants when used with the proper delivery and scavenging systems. The most commonly used, currently available inhalant anesthetics for mice and rats are isoflurane and sevoflurane. Both have applications in animal research due to their rapid onset and offset with minimal side effects.
Isoflurane: (Forane, 1-chloro-2,2,2-trifluoroethyldifluoromethyl ether) Halogenated ether that is clear, colorless, volatile liquid at standard temperature and pressure. It has a mild, ether-like odor and a molecular weight of 184.5.
Sevoflurane: (2,2,2-trifluoro-1-(trifluoromethyl) ethyl ether) Halogenated ether that is a sweet smelling, non-flammable fully fluorinated methyl isopropyl ether and has a molecular weight of 200.
Isoflurane and sevoflurane are the currently recommended inhalant anesthetics. Both of these agents require a precision vaporizer for delivery to the animal. Induction of mice or rats with these agents must be conducted in an induction chamber, where concentration is restricted to 5 percent. These are very rapid-acting inhalant anesthetics, and death can result during induction if the animal's condition is not monitored closely or if the concentration is too high.
An advantage of these agents is that they are not metabolized and therefore have little or no toxic effects. Also, they are relatively insoluble in blood, and therefore are “blown-off” quickly, providing a quick recovery. While very similar, isoflurane and sevoflurane have slightly different effects and mechanisms of action, even though the anesthetic result is nearly identical.
Anesthesia and Hypothermia
Animals under anesthesia are at increased risk of hypothermia. Because metabolisms are slowed and vital statistics are altered, and because animals are often shaved, loss of body temperature can be significant. Best practice dictates that the body temperatures of animal surgery subjects, like humans, be kept properly regulated during procedures. Failure to properly regulate temperature can cause the animal harm, and even mean the difference between the success or failure of a procedure. Infrared homeothermic warming is recognized as one of the most effective and safest methods for keeping an animal’s body temperature regulated.
—“Animals Principles of Rodent Asceptic Surgery & Perioptive Care,” Marcel Perret-Gentil, University Veterinarian & Director, Laboratory Animal Resources Center, The University of Texas at San Antonio.
Anesthesia Administration Systems for Mice and Rats
Precision vaporizers are part of an anesthesia machine and serve to mix oxygen with the anesthetic in a precisely-controlled concentration. Animal researchers who routinely incorporate surgery or the use of anesthetics in their animal experiments should consider purchasing an anesthesia machine. For safety, waste gas scavenging systems are required when using these agents. Precision vaporizers provide precise, controlled levels of anesthesia administered to the patient, providing a margin of safety to the animal. Using gas anesthetics at full concentration out of the bottle quickly results in overdosing the animal, and can kill very quickly.