Factors Affecting the Duration of Nembutal Anaesthesia in Rats

Abstract

At the end of 1946, one of us (F.H.S.) earried out a series of expei'iments in whieh were investigated various aspeets of Nembutal anaesthesia in rats at different body-temperatures. A year later these experiments were repeated (by K.H.S.) in full aud the results were statistically treated. Of the earlier series of tests, it is sufficient to say heie that tlie findings were fully supported and borne out in the later series, the results of which are here presented.In 1947, P'uhrnian published a paper covering part of the field of the present investigation, and used body-temporature as the measure of therm.il effects, rather than the environmental temperature as used by earlier workers. At high and low environmental temperatures, even without anaesthesia, small animals possess a fluctuating body-temperature; when they are anaesthetized, only the body temperature is a satisfactory thermal index.Here an attempt is made to point out the effects of body temperature and sex on tbe anaesthetic time and the mortality in rats injected with Nemhutal (sodium pentobarbital). THE EFFECT OF BODY TEMPERATURE.Brunton (1874) noticed that warmth prevented death in guinea-pigs given toxic doses of chloral hydrate, and suggested treatiug acute chloral poisoning with warmth. He used rectal temperatures in his work but most later workers, using barbiturates, did not. Raventos (1938), using Evipal in miee, found the duration of anaesthesia was 2-5 times as long at 20° C. as at 30° C, and shorter at 40° C. than at 30° C. Cameron (1939), giving pentobarbital to rats, found that the anaestbetic-time inereased as the environmental temperature decreased; he also fouud that warmth prevented death. Gaylord and Hodge (1J)44) showed a similar increase in anaesthctie-time with deerease of environmental temperature, when pentobarbital was injected subcutaneously into female rats.