The threshold for thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is reduced in the elderly

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 ?