Effect of different volatile anaesthetics on suxamethonium-induced jaw muscle contracture in rats.

Previous work has demonstrated that the interaction of hyperthermia and halothane may greatly increase the jaw muscle contracture produced by suxamethonium. We have compared the interaction of temperature and suxamethonium in the presence of halothane with the suxamethonium/temperature interaction of two other volatile anaesthetics, isoflurane and desflurane. Rats were anaesthetized with 1.35 MAC of halothane, isoflurane or desflurane. The jaw area was heated to 36-41 degrees C by a heating lamp while rectal temperature was maintained at 37 degrees C. Isometric tension was recorded from the jaw muscles. Suxamethonium 750 micrograms kg-1 i.v. induced a transient jaw muscle contracture (JMC) during halothane, isoflurane and desflurane anaesthesia. JMC exhibited significant dependence on jaw muscle temperature with all three volatile anaesthetics. Increasing the temperature of the jaw area from 37 degrees C to 41 degrees C increased JMC 8.7-fold with halothane, 8.8-fold with isoflurane and 3.1-fold with desflurane. The difference between halothane and desflurane was significant. While suxamethonium-induced JMC was dependent on temperature for all three volatile anaesthetic, the temperature dependence appeared to be less with desflurane.