The Threshold for Thermoregulatory Vasoconstriction During Nitrous OxideBevoflurane Anesthesia Is Reduced in the Elderly Makoto Ozaki, MD*, Daniel I. Sessler, Mm, Takashi Matsukawa, MDS, Kyoko Ozaki, MD*, Kenji Atarashi, MD*, Chiharu Negishi, MD*, and Hidehiro Suzuki, MD* *Department of Anesthesiology, Tokyo Women’s Medical College, Tokyo, Japan; tOutcomes Research Laboratory, Department of Anesthesia, University of California, San Francisco, California and Department of Anesthesia and Critical Care, University of Vienna, Vienna, Austria; and SDepartment of Anesthesiology, Yamanashi Medical University, Yamanashi, Japan Elderly patients become more hypothermic during sur- gery, shiver less postoperatively, and take longer to re- warm than younger patients. Similarly, the vasocon- striction threshold (triggering core temperature) is reduced approximately 1°C in elderly patients during nitrous oxide / isoflurane anesthesia. Accordingly, we tested the hypothesis that the vasoconstriction thresh- old in the elderly is also reduced approximately 1°C during nitrous oxide and sevoflurane anesthesia. Eleven young patients aged 30-50 yr and 14 elderly patients aged 60-80 yr were anesthetized with ni- trous oxide (50%) and sevoflurane (1%). Mean skin temperature was calculated from four sites. Fingertip blood flow was estimated using forearm minus finger- tip skin-temperature gradients, with a gradient of 0°C identifying onset of vasoconstriction. The distal esoph- ageal temperature triggering onset of vasoconstriction identified the threshold for this thermoregulatory de- fense. The data from five patients who did not vasocon- strict at minimum core temperatures of 33-34°C were eliminated, leaving 10 patients in each group. The vaso- constriction threshold was significantly less in the el- derly (35.0 2 0.8”C) than in younger patients (35.8 ? 0.3”C), despite similar mean skin temperatures (mean ? SD, P < 0.01, Student’s t-test). Age dependence of thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is similar to that previ- ously observed during nitrous oxide / isoflurane anesthesia. (Anesth Analg 1997;84:1029-33) I ntraoperative core hypothermia results initially from redistribution of body heat (1) and, subse- quently, from heat loss exceeding metabolic heat production (2). After several hours, however, core temperature reaches a plateau and does not decrease further (3). This plateau coincides with the reemer- gence of thermoregulatory vasoconstriction that de- creases cutaneous heat loss (4) and constrains meta- bolic heat to the core thermal compartment (5). Thermoregulatory vasoconstriction thus minimizes Supported by National Institutes of Health grant GM49670, the Joseph Drown Foundation (Los Angeles, CA), and the Anesthesia Patient Safety Foundation (Ermire, PA). Mallinckrodt Anesthesiology Products, Inc. (St. Louis, MO) do- nated the thermocouples we used. The authors do not consult for, accept honoraria from, or own stock or stock options in any anesthesia-related company. Accepted for publication January 10, 1997. Address correspondence and reprint requests to Daniel I. Sessler, MD, Department of Anesthesia, 374 Parnassus Ave., University of California, San Francisco, CA 94143-0648. Address e-mail to sessler@vaxine.ucsf.edu. 01997 by the International Anesthesia Research Society 0003-2999/97/$5.00 further core hypothermia during anesthesia. Because intraoperative hypothermia is associated with numer- ous adverse outcomes (6-8), the threshold for thermo- regulatory vasoconstriction is clinically important. Multiple observations suggest that thermoregula- tory control is impaired in the elderly. Elderly patients become more hypothermic during surgery (9-ll), shiver less during spinal anesthesia (12) and after general anesthesia (9,13), and take longer to rewarm postoperatively (10) than younger patients. Similarly, accidental hypothermia (core temperature <36”C) is relatively common in the elderly (14,15) but is rare in younger individuals unless they are predisposed to the condition by intoxication (16) or extreme environ- mental exposure (17). Consistent with impaired thermoregulatory control, the vasoconstriction threshold (triggering core tem- perature) is reduced approximately 1°C in elderly pa- tients during nitrous oxide/isoflurane anesthesia (18). However, it remains unknown whether intraoperative thermoregulatory control is similarly impaired by An&h Analg 1997;84:1029-33 1029