Differential increase in potency of neuromuscular blocking agents by enflurane and halothane

Cumulative dose-response curves of suxamethonium, tubocurarine, and pancuronium were constructed in 142 patients under enflurane and halothane anesthesia, and neuroleptic anesthesia (control group). The dose-response curves shifted to the left with increasing inspired concentrations of enflurane and halothane, thus indicating an increase in neuromuscular blocking potency. An evaluation of the ED50 shows that this increase is quite different for the three relaxants studied. Enflurane has a significantly greater synergistic effect than halothane. Beside other mechanisms and sites of action, which are briefly discussed, the recently proposed transient-state concept of relaxant-receptor interaction is applied to explain the increase in affinity at the receptor level.