In vivo induced malignant hyperthermia in pigs. I. Physiological and biochemical changes and the influence of dantrolene sodium.

The effects of an induced malignant hyperthermia (MH) crisis have been studied in the intact pig. Both physiological and biochemical changes in skeletal muscle were studied. MH was induced with 3% halothane plus a bolus injection of succinylcholine. In the prechallenge period a significant difference was observed in the concentration of certain muscle metabolites, comparing the MH-susceptible (MH+) with the non-susceptible (MH-) pigs. A lower level was measured for phosphocreatine (PCr), inosine monophosphate (IMP) and an increased level of lactate and creatine (Cr) in the susceptible pigs (MH+). The challenge caused a significant reduction of the level of PCr and adenosine in MH+ pigs, compared to the prechallenge period. After administration of dantrolene sodium, a significant decrease was measured in the level of lactate, compared to the prechallenge period as well as during the challenge. In contrast, in the control pigs no significant changes were observed in muscle metabolites, either after induction of MH or after the administration of dantrolene sodium. Enzyme activity determinations of muscle adenylate kinase and adenosine monophosphate (AMP)-deaminase did not show any difference in activity either before or during the MH crisis or after treatment with dantrolene sodium. The earliest physiological change during an induced MH crisis in our study was the rapid increase of the end-tidal CO2. Within 5 min after MH induction, end-tidal CO2 was doubled. It is concluded that the monitoring of the end-tidal CO2 is essential to diagnose MH at a very early stage.