Influence of propranolol on the in vitro response to caffeine and halothane in malignant hyperthermia-susceptible muscle.

In vitro contracture tests for susceptibility to malignant hyperthermia (MH) were performed with halothane and caffeine in 27 patients according to the protocol of the European MH Group. Additional halothane and caffeine tests were performed in the presence of propranolol 80 micrograms/l. Contractures after exposure to halothane were seen only in MH-susceptible (MHS) patients (n = 12), and were not affected by propranolol. In contrast, propranolol shifted the caffeine dose-response curve to the right and significantly increased the caffeine threshold in the MHS group. Propranolol did not influence the caffeine results in the normal response group group (n = 12). It is concluded that beta-blockers should be discontinued before investigation for MH susceptibility.