The effect of sevoflurane and isoflurane on the neuromuscular block produced by vecuronium continuous infusion

Volatile anesthetics enhance the action of neuromuscular blockade to various degrees, although the influence of sevoflurane on the neuromuscular block has not yet been characterized. The purpose of this investigation is to determine the vecuronium infusion rate requirement under sevoflurane anesthesia and to compare it to that of isoflurane anesthesia. Twenty patients scheduled for otorhinolaryngologic surgery were randomly assigned to receive either sevoflurane (SEV) or isoflurane (ISO) at 1 minimum alveolar anesthetic concentration (MAC) (1.7% and 1.2%, respectively) in combination with 67% nitrous oxide. Anesthesia was induced with 5 mg/kg thiopental and muscle relaxation was obtained by a bolus of vecuronium 0.1 mg/kg followed by a continuous vecuronium infusion to achieve 90% muscle relaxation. The plasma concentrations of vecuronium (C-VEC) and 3-desacetylvecuronium (C-DES) at steady state were measured with a gas chromatographic assay. There was no difference between SEV and ISO in the following variables: the vecuronium infusion rate requirement to achieve 90% muscle relaxation (0.42 +/- 0.11 [SEV] vs 0.40 +/- 0.10 [ISO] mu g . kg(-1). min(-1)), C-VEC (144.4 +/- 38.1 [SEV] vs 149.7 +/- 69.2 [ISO] ng/mL), C-DES (57.2 +/- 20.3 [SEV] vs 65.3 +/- 26.1 [ISO], ng/mL), and plasma vecuronium clearance (2.85 +/- 0.86 [SEV] vs 3.19 +/- 1.24 [ISO] mL . kg(-1). min(-1)). This study indicates that SEV at 1 MAC requires a vecuronium infusion rate similar to that of ISO at 1 MAC to achieve 90% muscle relaxation.