Role of sympathetic activity in porcine malignant hyperthermia.

Abstract

Malignant hyperthermia (MH) is characterized in part by sympathetic hyperactivity associated with increased levels of circulating catecholamines. Controversy exists as to whether the sympathetic nervous system is in some way abnormal and primarily contributing to MH, or whether the sympathetic response is secondary to the stress of MH originating from skeletal muscle. Total spinal anesthesia with resulting sympathetic denervation was used in genetically susceptible Poland China swine to investigate this question. isobaric tetracaine, 1.2–2.2 mg/kg, was injected via the sacral hiatus into the cerebrospinal fluid to produce total spinal anesthesia (paralysis of all four limbs). Total spinal anesthesia failed to prevent the occurrence or attenuate the course of MH in swine given halothane, 1 per cent (five pigs) or halothane and succinylcholine, 3 mg/kg (one pig). Total spinal anesthesia did prevent the expected increases in norepinephrine and epinephrine during MH in all six swine. Since dantrolene is specifically therapeutic in MH, its effect on the sympathetic response to stress was measured in two other susceptible swine. Treatment with dantrolene, 10 mg/kg, intravenously, did not prevent increases in catecholamines due to stress caused by either respiratory and metabolic acidosis (Paco2 110 torr, base excess −20) combined or hemorrhagic hypotension (mean pressure 40 torr). The authors conclude that the sympathetic nervous system is involved in porcine MH only as a secondary response to stress; that conduction anesthesia will not protect pigs from MH; and that the efficacy of dantrolene in porcine MH is due to its effects on skeletal muscle rather than to depression of the sympathetic nervous system.