Vecuronium-induced Neuromuscular Blockade during Enflurane, Isoflurane, and Halothane Anesthesia in Humans

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Abstract
To determine the effect of the commonly used volatile anesthetics on a vecuronium-induced neuromuscular blockade, 54 patients anesthetized with 1.2 or 2.2 MAC [mininum anesthetic concentration] enflurane, isoflurane or halothane were studied (MAC value includes contribution from 60% N2O). During 1.2 MAC enflurane, isoflurane and halothane, the ED50 (the doses depressing twitch tension 50%) for vecuronium were 12.8, 14.7 and 16.9 .mu.g/kg, respectively. During 2.2 MAC enflurane, isoflurane and halothane, the ED50 for vecuronium were 6.3, 9.8 and 13.8 .mu.g/kg, respectively (P < 0.05). Time from inejction to peak effect was the same for each anesthetic group (6.5 .+-. 0.5 min, mean), except for the group given 2.2 MAC enflurane (9.7 .+-. 0.6 min) (P < 0.05). The duration of a 50% block from injection to 90% recovery was the same for each group (mean 20 .+-. 4 min), except for the group given 2.2 MAC enflurane (46.5 min) (P < 0.05). Evidently enflurane is the most potent volatile anesthetic, followed by isoflurane and then halothane, in augmenting a vecuronium-induced neuromuscular blockade. Increasing the concentration of volatile anesthetic has less effect on a neuromuscular blockade produced by vecuronium than on one produced by other nondepolarizing relaxants (e.g., pancuronium and d-tubucurarine).

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