Thermoregulatory responses to hyperthermia during isoflurane anesthesia in humans

Abstract

The authors tested the hypotheses that isoflurane anesthesia increases the threshold for sweating but minimally decreases the gain (sensitivity) or maximum intensity of this response and that thermoregulatory responses to hyperthermia are similar in anesthetized men and women. Sweating in response to core hyperthermia was studied in five men and five women during 0, 0.8, and 1.2% end-tidal isoflurane anesthesia. Thigh sweating was quantified by measuring gas flow, relative humidity, and temperature passing over a known surface area. The distal esophageal temperature triggering sweating was considered the sweating threshold, and gain was defined as the core temperature increment required to increase sweating rate from 25 to 75% of maximum observed intensity. The sweating threshold increased linearly with isoflurane concentration from 36.6 +/- 0.1 to 38.1 +/- 0.1 degrees C in the men and from 37.1 +/- 0.3 to 38.3 +/- 0.2 degrees C in the women. The thresholds were significantly higher in women than in men. Gain and maximum sweating intensities were similar at each anesthetic concentration and in men and women. These data indicate that isoflurane anesthesia significantly increases the threshold triggering thermoregulatory sweating but that gain and maximum sweating rate are relatively well preserved.

The effect of nitrous oxide-induced narcosis on aerobic work performance

“…Our observation that the onset of sweating was unaected during narcosis contradicts previous ®ndings that the sweating threshold is increased when subjects are passively heated during en¯urane and iso¯urane anaesthesia (Lopez et al 1993;Washington et al 1993). In contrast, our ®ndings of no change in the gain of the sweating response are in agreement with these earlier studies.…”

“…Also, the possibility that the level of anaesthesia aects the sweating threshold cannot be excluded. Our study was conducted with an analgesic level of anaesthetic gas, whereas previous studies, which observed an elevated threshold for sweating (Lopez et al 1993;Washington et al 1993), were conducted on subjects under general anaesthesia.…”

Skin-temperature gradients are a validated measure of fingertip perfusion

“…In fact, since 1995, the dose-dependent effects of all major intravenous (Matsukawa et al 1995) and volatile (Annadata et al 1995) anesthetics on sweating, vasoconstriction, and shivering thresholds have been quantified. gain and maximum intensity of sweating (Washington et al 1993), vasoconstriction (Kurz et al 1995b), and shivering (Ikeda et al 1998) have been determined. The thermoregulatory effects of general anesthetics was reviewed in the New England Journal of Medicine (Sessler 1997).…”

Hypothermia – it's more than a toy

“…The gain and maximum response intensity of sweating and active vasodilation are well preserved in patients given volatile anesthetics [6]. Desflurane, however, reduces the gain of arterio-venous shunt vasoconstriction 3-fold, without altering the maximum intensity [10].…”

“…General anesthetics linearly increase the warm-response thresholds [5][6][7]. Opioids [8] and the intravenous anesthetic propofol [9] linearly decreases the vasoconstriction and shivering thresholds.…”