Sweating threshold during isoflurane anesthesia in humans.

Isoflurane anesthesia in humans markedly decreases the threshold temperature triggering peripheral thermoregulatory vasoconstriction (i.e., central temperature triggering vasoconstriction). However, it is not known whether the sweating threshold remains unchanged (e.g., near 37 degrees C), decreases along with the vasoconstriction threshold, or increases during anesthetic administration. Accordingly, the hypothesis that isoflurane anesthesia increases the thermoregulatory threshold for sweating was tested. Forehead sweating was evaluated in five healthy patients given isoflurane anesthesia. The sweating threshold was prospectively defined as the distal esophageal temperature at which significant sweating was first observed. Sweating was observed in each patient at a mean central temperature of 38.3 +/- 0.3 degrees C and an end-tidal isoflurane concentration of 1.1% +/- 0.2%. The interthreshold range (difference between vasoconstriction and sweating thresholds) without anesthesia is approximately 0.5 degrees C; isoflurane anesthesia increases this range to approximately 4 degrees C.