Isoflurane and Sevoflurane Produce a Dose-Dependent Reduction in the Shivering Threshold in Rabbits

Abstract

All general anesthetics markedly impair thermoregulatory responses; nonetheless, sufficient hyperthermia or hypothermia will trigger most protective reflexes. Shivering, however, remains an exception among thermo-regulatory responses: it is common during postanesthetic recovery, but is rare at typical anesthetic concentrations. This observation suggests that general anesthesia impairs shivering far more than other thermoregulatory defenses. Accordingly, we tested the hypothesis that low concentrations of isoflurane and sevoflurane would virtually obliterate shivering. Japanese white rabbits were anesthetized with isoflurane or sevoflurane at end-tidal concentrations of 0.2, 0.3, and 0.4 minimum alveolar anesthetic concentration (MAC) (n = 6 in each group); the normal core temperature for these rabbits is approximately 39 degrees C. Core temperatures were subsequently reduced by a water-perfused thermode positioned in the colon. The core temperature triggering shivering identified the threshold for this response. Five of the six rabbits given 0.2 MAC isoflurane shivered at a mean core temperature of 36.3 +/- 0.3 degrees C (mean +/- SD), and one rabbit failed to shiver at a minimum core temperature of 35.0 degrees C. Four of the six rabbits given 0.3 MAC isoflurane shivered at a mean core temperature of 36.2 +/- 0.6 degrees C, and two of these rabbits failed to shiver at a minimum core temperature of 35.0 degrees C. However, no rabbit given 0.4 MAC isoflurane shivered, even at minimum core temperatures of 35.0 degrees C. All of the rabbits given 0.2 MAC sevoflurane shivered at a mean core temperature of 36.6 +/- 0.7 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of endotoxin and cytokines in the systemic inflammatory response to heat injury

“…The ability of IL-1ra to regulate CNS levels of serotonin and protect against cerebral edema / ischemia suggests a neuroprotective role for this cytokine (77). Although the IL-1ra significantly prolongs heat stroke survival time (by ~100 minutes ) in all studies in which it has been tested, it is important to note that these studies were conducted in anesthetized animals (i.e., anesthesia compromises autonomic and behavioral thermoregulatory mechanisms; (95,96)) and the animals eventually succumbed to heat stroke despite the treatment; thus, it remains unclear if IL-1ra is protective against long-term heat stroke mortality, such as days, weeks, months or years following collapse.…”