Desflurane Slightly Increases the Sweating Threshold but Produces Marked, Nonlinear Decreases in the Vasoconstriction and Shivering Thresholds

BACKGROUND: Shivering is rare during general anesthesia. This observation suggests that anesthetics profoundly impair shivering. However, the effects of surgical doses of volatile anesthetics on control of shivering have yet to be evaluated. Furthermore, the effects of desflurane on sweating and thermoregulatory vasoconstriction remain unknown. Accordingly, the authors determined the concentration-dependent effects of desflurane on sweating, vasoconstriction, and shivering. METHODS: Nine volunteers each were studied on three randomly ordered days: (1) control (no anesthesia); (2) a target end-tidal desflurane concentration of 0.5 minimum alveolar concentration (MAC; 3.5%); and (3) a target concentration of 0.8 MAC (5.6%). Each day, volunteers were warmed until sweating was induced and subsequently cooled until peripheral vasoconstriction and shivering was observed. Changes in skin temperature were arithmetically compensated using the established linear cutaneous contributions to control of each response. From the calculated thresholds (core temperatures triggering responses at a designated skin temperature of 34 degrees C), the concentration-response relationship was determined. RESULTS: Desflurane significantly and linearly increased the sweating threshold from 37.1 +/- 0.3 degrees C on the control day (mean +/- SD), to 37.6 +/- 0.4 degrees C at 0.5 MAC, and to 38.1 +/- 0.3 degrees C at 0.8 MAC. Desflurane significantly, but nonlinearly, reduced the vasoconstriction and shivering thresholds. The sweating-to-vasoconstriction (interthreshold) range thus increased from 0.5 +/- 0.3 degrees C to 2.3 +/- 0.7 degrees C at 0.5 MAC and further to 4.6 +/- 2.0 degrees C at 0.8 MAC. The vasoconstriction-to-shivering range (difference between the respective thresholds) remained between 1.1 and 1.5 degrees C on the three study days. CONCLUSIONS: The observed linear increase in the sweating threshold was similar in pattern and magnitude to that produced by most general anesthetics. The approximately 3 degrees C reduction in the vasoconstriction threshold by 0.8 MAC desflurane was similar to that observed previously during isoflurane and propofol anesthesia. However, the threshold was reduced less than expected at 0.5 MAC, suggesting that the dose-response relationship for vasoconstriction is nonlinear. Shivering was induced without difficulty in this study although the response is rare in surgical patients. It is likely that shivering during general anesthesia is rare because thermoregulatory vasoconstriction usually prevents body temperature from decreasing the required additional 1-1.5 degrees C.