Adult body temperature and heated humidification of anesthetic gases during general anesthesia

To determine the effects on body temperature of heating and humidifying inspired anesthetic gases to 37 C and 100% relative humidity, 42 men who had major surgical procedures under general anesthesia were studied. Group 1 (control) consisted of 10 patients who inspired gases from a standard semicircle absorber system with no added humidity. The mean nasopharyngeal temperature decreased significantly from 36.2 +/- 0.1 C to 34.9 +/- 0.2 C. Ten other patients, group 2, inspired gases that were heated and humidified. Mean nasopharyngeal temperature was maintained at 36.4 +/- 0.2 C with no significant changes throughout the study. One patient in this group became hypothermic, but only transiently. Ten patients, group 3, were allowed to become hypothermic before gases were heated and humidified. The mean nasopharyngeal temperature increased significantly from 34.7 +/- 0.2 C to 36.0 +/- 0.3 C during 4 hours of heated humidification. For groups 4 and 5, six patients each, gases were heated and humidified on alternate hours. The responses of the two groups demonstrated a causal relationship between the heating and humidifying of inspired gases and an increased mean nasopharyngeal temperature. It is concluded that heating and humidifying gases to 37 C and 100% relative humidity effectively maintains normothermia and rewarms hypothermic adults during general anesthesia.