The role of sympathetic activity in initiating malignant hyperthermia.

The role of sympathetic activity in triggering malignant hyperthermia (MH) is controversial. Increased sympathetic activity has been considered by some to be the causal factor, whilst other believe this activity to be secondary to metabolic events in the MH syndrome. In this study, a number of parameters, including the blood levels of noradrenaline and adrenaline, were followed in pigs susceptible to MH during exposure to halothane. Seven pigs, crossbreeds of Swedish Landrace and Yorkshire, females and castrated males, aged about 9 months were used. Results are presented for individual pigs. One of the pigs was a non-responder. The time of onset for different signs of MH varied greatly, as judged by ten independent observers. Onset of changes in heart rate, muscle temperature, blood PCO2 and pH, plasma adrenaline and noradrenaline could be scored. The metabolic events (increased PCO2 and decreased pH in blood) significantly preceded the signs of increased sympathetic activity (increased heart rate and elevated levels of catecholamines in blood). Our results support the view that increased sympathetic activity does not initiate MH. The sympathetic activity, however, strongly contributes to the fulminant MH syndrome.