Continuous Infusion of Vecuronium

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Abstract
The authors studied the effects of enflurane, isoflurane, and fentanyl, each in combination with 60% nitrous oxide, on the vecuronium infusion rate necessary to maintain constant 90% depression of control muscle twitch tension. Thirty healthy surgical patients were given an initial 0.1 mg/kg bolus of vecuronium, followed by an infusion of vecuronium at an initial rate of 1.0 .mu.g .cntdot. kg-1 .cntdot. min-1. After 1 h of steady-state 90% twitch depression, plasma vecuronium concentrations (Css90) were measured by capillary column gas chromatography. Total plasma clearance of vecuronium was estimated using Css90 values. Vecuronium infusion rates (mean .+-. SD) were similar for patients given enflurane (0.28 .+-. 0.13 .mu.g .cntdot. kg-1 .cntdot. min-1) and isoflurane (0.30 .+-. 0.13 .mu.g .cntdot. kg-1 .cntdot. min-1), but significantly higher in patients given fentanyl (0.92 .+-. 0.37 .mu.g .cntdot. kg-1 .cntdot. min-1). Values for Css90 in the patients receiving enflurane and isoflurane were similar (71 .+-. 34 and 72 .+-. 44 ng/ml, respectively), but significantly higher in those receiving fentanyl (165 .+-. 48 ng/ml). Total plasma clearance was similar during enflurane, isoflurane, and fentanyl anesthesia (4.4 .+-. 2.6, 4.6 .+-. 1.2, and 5.6 .+-. 1.9 ml .cntdot. kg-1, respectively). The authors conclude that patients receiving isoflurane and enflurane require markedly lower vecuronium infusion rates to achieve 90% neuromuscular blockade than those receiving fentanyl. The enhancement of neuromuscular blockade by isoflurane and enflurane represents a change in the pharmacodynamics of vecuronium-induced neuromuscular blockade, rather than a change in pharmacokinetics.