THE THRESHOLD FOR THERMOREGULATORY VASOCONSTRICTION DURING NITROUS-OXIDE SEVOFLURANE ANESTHESIA IS REDUCED IN THE ELDERLY

Elderly patients become more hypothermic during surgery, shiver less p ostoperatively, and take longer to rewarm than younger patients. Simil arly, the vasoconstriction threshold (triggering core temperature) is reduced approximately 1 degrees C in elderly patients during nitrous o xide/isoflurane anesthesia. Accordingly, we tested the hypothesis that the vasoconstriction threshold in the elderly is also reduced approxi mately 1 degrees C during nitrous oxide and sevoflurane anesthesia. El even young patients aged 30-50 yr and 14 elderly patients aged 60-80 y r were anesthetized with nitrous oxide (50%) and sevoflurane (1%). Mea n skin temperature was calculated from four sites. Fingertip blood flo w was estimated using forearm minus fingertip skin-temperature gradien ts, with a gradient of 0 degrees C identifying onset of vasoconstricti on. The distal esophageal temperature triggering onset of vasoconstric tion identified the threshold for this thermoregulatory defense. The d ata from five patients who did not vasoconstriction at minimum core te mperatures of 33-34 degrees C were eliminated, leaving 10 patients in each group. The vasoconstriction threshold was significantly less in t he elderly (35.0 +/- 0.8 degrees C) than in younger patients (35.8 +/- 0.3 degrees C), despite similar mean skin temperatures (mean +/- so, P < 0.01, Student's t-test). Age dependence of thermoregulatory vasoco nstriction during nitrous oxide/sevoflurane anesthesia is similar to t hat previously observed during nitrous oxide/isoflurane anesthesia.