THE CATECHOLAMINE, CORTISOL, AND HEMODYNAMIC-RESPONSES TO MILD PERIOPERATIVE HYPOTHERMIA - A RANDOMIZED CLINICAL-TRIAL

Background: Unintended hypothermia occurs frequently during surgery an d may have adverse effects on the caidiovascular system. Although the mechanisms responsible for the cardiovascular manifestations of hypoth ermia are unclear, it is possible that they are sympathetically mediat ed. In this prospective study, relationships between body temperature, the neuroendocrine response, and hemodynamic changes in the periopera tive period were examined. Methods: Seventy-four elderly patients, und ergoing abdominal, thoracic, or lower extremity vascular surgical proc edures, were randomly assigned to either ''routine care'' (n = 37) or ''forced-air warming'' (n = 37) groups. Throughout the intraoperative and early postoperative periods, the routine care group received stand ard thermal care, and the forced-air warming group received forced-air skin-surface warming. Core temperature, forearm minus fingertip skin- surface temperature gradient, and plasma concentrations of epinephrine , norepinephrine, and cortisol were measured throughout the perioperat ive period, and the two groups were compared. in addition, heart rate and arterial blood pressure were compared between groups. Results: The routine care and forced-air warming groups did not differ with regard to age, sex, type of surgical procedures, anesthetic techniques, or p ostoperative analgesia. Mean core temperature was lower in the routine care group on admission to the postanesthetic care unit (routine care , 35.3 +/- 0.1 degrees C; forced-air warming, 36.7 +/- 0.1 degrees C; P = 0.0001) and remained lower during the early postoperative period. Forearm minus fingertip skin-surface temperature gradient (an index of peripheral vasoconstriction) was greater in the routine care group in the early postoperative period. The mean norepinephrine concentration (pcg/ml) was greater in the routine care group immediately after surg ery (480 +/- 70 vs. 330 +/- 30, P = 0.02) and at 60 min (530 +/- 50 vs . 340 +/- 30, P = 0.002) and 180 min (500 +/- 80 vs. 320 +/- 30, P = 0 .004) postoperatively. Mean epinephrine concentrations were not signif icantly different between groups. Mean cortisol concentrations were in creased in both groups during the early postoperative period (P < 0.01 ), but the differences between groups were not significant. Systolic, mean, and diastolic arterial blood pressures were significantly higher in the routine care group. Conclusions: Compared with patients in the forced-air warming group, patients receiving routine thermal care had lower core temperatures, a greater degree of peripheral vasoconstrict ion, higher norepinephrine concentrations, and higher arterial blood p ressures in the early postoperative period. These findings suggest a p ossible mechanism for hypothermia-related cardiovascular morbidity in the perioperative period.