Core hypothermia and skin-surface temperature gradients. Epidural versus general anesthesia and the effects of age

Inadvertent hypothermia occurs frequently during surgery and may be associated with adverse outcomes. Although various anesthetic agents have been shown to impair thermoregulation, the impairment with regional and general anesthetics has not been directly compared.

Thirty patients undergoing radical retropubic prostatectomy were randomly allocated to receive epidural (EA, n = 15) or general (GA, n = 15) anesthesia. Tympanic membrane measurements were used to assess core temperature. Forearm and calf skin-surface temperature gradients were used to assess thermoregulatory vasoconstriction (forearm minus fingertip > 4 degrees C and calf minus toe > 6 degrees C). The two groups were compared during the intraoperative and early postoperative periods to identify differences. Subgroup analysis was used to compare core temperatures and skin-surface gradients in younger (< 62 yr of age) and older (> or = 62 yr) patients in the EA and GA groups.

Mean tympanic membrane temperatures were similar at all time periods in the EA and GA groups and were nearly identical at the end of the surgical procedure (EA, 35.5 +/- 0.2 degrees C; GA, 35.6 +/- 0.2 degrees C) (P = 0.68). Intraoperatively, the EA group maintained a significant forearm skin-surface gradient compared to the GA group (P = 0.0001), whereas the calf gradients were minimal and were similar between groups. Postoperatively, both groups had comparable positive forearm gradients, whereas calf gradients were greater in the GA group (P = 0.001). Mean core temperatures and forearm gradients were not different between the younger and older patients receiving GA. In those receiving EA, the younger patients had greater mean core temperatures (P = 0.015) and greater forearm gradients (P = 0.05) for most of the perioperative period.

The EA and GA groups had virtually identical core temperature profiles during the intraoperative and post-operative periods. Comparison of skin-surface gradients suggests that EA is associated with less intraoperative upper-body thermoregulatory impairment but greater and persistent post-operative lower-body impairment. During EA, younger patients appeared to maintain thermoregulatory activity relative to the older patients. In patients receiving GA, the age-related differences were minimal.