Quantitation of the Effect of Nitrous Oxide on Rocuronium Infusion Requirements Using Closed-loop Feedback Control

Abstract

Background Nitrous oxide has a minor effect on the effective dose 50% values of bolus doses of rocuronium. The authors have studied the effect of nitrous oxide on the infusion requirements of rocuronium using closed-loop feedback control of rocuronium infusion. Methods The authors obtained institutional approval and informed consent to study 70 patients. The patients were given total intravenous anesthesia with propofol and remifentanil by target-controlled infusion and were randomly assigned to one of two groups, one receiving nitrous oxide with 30% oxygen (n = 35) and the other group receiving air with 30% oxygen (n = 35). The possible interaction of rocuronium with nitrous oxide was quantitated by determining the asymptotic steady state rate of infusion of rocuronium necessary to produce a constant 90% neuromuscular block. This was accomplished by applying nonlinear curve fitting to data on the cumulative dose requirement during the initial 90-min period after bolus administration of rocuronium. Results Patient characteristics and controller performance, i.e., the ability of the controller to maintain the neuromuscular block constant at the set point, did not differ significantly between the groups. The administration of nitrous oxide did not affect rocuronium infusion requirements. The mean steady state rates of infusion were 33.0 +/- 9.8 and 36.9 +/- 13.2 mg/h in the nitrous oxide-total intravenous anesthesia and air-total intravenous anesthesia groups, respectively. Conclusions Nitrous oxide does not affect the infusion requirements of rocuronium to a clinically significant degree.