PRIOR HYPOTHERMIA ATTENUATES MALIGNANT HYPERTHERMIA IN SUSCEPTIBLE SWINE

This study was designed to determine the extent by which mild or moder ate hypothermia attenuates the triggering of malignant hyperthermia (M H) induced by the combined administration of halothane and succinylcho line. Sixteen susceptible swine were initially anesthetized with nontr iggering drugs and then either kept normothermic (approximate to 38 de grees C, n = 6) or cooled to induce mild (approximate to 35 degrees C, n = 6), or moderate (approximate to 33 degrees C, n = 4) hypothermia. Next, after a 30-min control period, the normothermic and mildly hypo thermic animals were administered 1 minimum alveolar anesthetic concen tration (MAC) halothane followed by a bolus dose of succinylcholine (2 mg/kg). Within 10 min all normothermic animals developed fulminant MH , whereas the onset of MH was slowed or was absent in the mildly hypot hermic group. To test whether moderate hypothermia could more effectiv ely minimize the signs of a MH episode, this group of animals was expo sed to 1.5 MAC halothane followed 10 min later by a 3-mg/kg bolus of s uccinylcholine. MH was not induced and anesthesia was then changed to nontriggering drugs (ketamine and pancuronium). The animals were then aggressively rewarmed to 38 degrees C: a slight increase in the ETco(2 ) was detected, but MH episodes did not spontaneously occur. Subsequen tly, the readministration of halothane and succinylcholine rapidly pro voked fulminant MH. We concluded that the induction of mild hypothermi a impairs triggering and reduces the progression of MH induced by the combined administration of halothane and succinylcholine, whereas mode rate hypothermia was completely protective and thus could be considere d for prophylaxis.