Fig. 8. Heat balance during epidural anesthesia. Overall heat balance was only slightly negative (loss exceeding production) before induction of anesthesia and subsequently changed little. To separate the contributions of decreased overall heat balance and internal redistribution of body heat to the decrease in core temperature, the change in overall heat balance was divided by body weight and the specific heat of humans. The resulting change in mean body temperature (mean body) was subtracted from the change in core temperature (core), leaving the core hypothermia specifically resulting from redistribution (redistribution). After 1 h of anesthesia, core temperature decreased 0.8 ± 0.3°C, with redistribution contributing 89% to the decrease. During the subsequent 2 h of anesthesia, core temperature decreased an additional 0.4 ± 0.3°C, with redistribution contributing 62%. Redistribution contributed 80% to the entire 1.2 ± 0.3°C decrease in core temperature during the 3 h of anesthesia. The increase in the redistribution curve before induction of anesthesia indicates that thermoregulatory vasoconstriction was constraining metabolic heat to the core thermal compartment. Such constraint is, of course, the only way in which core temperature could increase while body heat content decreased. Induction of epidural anesthesia is identified as elapsed time zero. Results are presented as the mean ± SD. Reprinted with permission from Matsukawa et al. 26