EPIDURAL VERSUS GENERAL-ANESTHESIA, AMBIENT OPERATING-ROOM TEMPERATURE, AND PATIENT AGE AS PREDICTORS OF INADVERTENT HYPOTHERMIA

To elucidate the multifactorial nature of perioperative changes in body temperature, the influence of several clinical variables, including anesthetic technique, ambient operating room temperature, and age, were evaluated. Perioperative oral sublingual temperatures were measured in 97 patients undergoing tower extremity vascular surgery randomized to receive either general (GA) or epidural (EA) anesthesia. Surgery and anesthesia were performed in operating rooms (OR) with a relatively warm mean ambient temperature (24.5 +/- 0.4-degrees-C) (GA, n = 30; EA, n = 33) or relatively cold mean ambient temperature (21.3 +/- 0.3-degrees-C) (GA, n = 21; EA, n = 13). Patients were 35-94 yr old, with a mean age of 64.5 +/- 1.1 yr. A regression analysis was performed to determine the variables that correlated with intraoperative decrease in temperature and postoperative rewarming rate. The major correlates of greater intraoperative decrease in temperature were 1) GA (P = 0.003); 2) cold ambient OR temperature (P = 0.07); and 3) advancing patient age (P = 0.03). There was significant interaction between ambient OR temperature and type of anesthesia (P = 0.03): there was a greater intraoperative decrease in temperature with GA compared to EA in a cold OR but a similar decrease with GA and EA in a warm OR. The data also suggest an interaction between type of anesthesia and patient age (P = 0.06), showing a greater decrease in temperature with GA compared to EA in the younger patients, but a similar decrease between GA and EA in older patients. Age was the only significant determinant of postoperative rewarming rate, with the older patients taking longer to rewarm (P = 0.0003). The results suggest that temperature is reduced by GA to a greater degree than by EA when ambient OR temperature is cold, but this difference between GA and EA is not significant when ambient OR temperature is relatively warm. Also, the ability to maintain temperature during anesthesia decreases with advancing age.