QUANTIFYING THE INTERACTION OF ROCURONIUM (ORG-9426) WITH ETOMIDATE, FENTANYL, MIDAZOLAM, PROPOFOL, THIOPENTAL, AND ISOFLURANE USING CLOSED-LOOP FEEDBACK-CONTROL OF ROCURONIUM INFUSION

The present study was designed to evaluate the interactions of rocuron ium with etomidate, fentanyl, midazolam, propofol, thiopental, and iso flurane using closed-loop feedback control of infusion of rocuronium. Sixty patients were randomly assigned to one of six sequences where an esthesia was maintained with etomidate, fentanyl, midazolam, propofol, or thiopental and nitrous oxide, or with isoflurane and nitrous oxide . The possible interaction of rocuronium with the anesthetics was quan tified by determining the asymptotic steady-state rate of infusion (I( ss)) of rocuronium necessary to produce a constant 90% neuromuscular b lock. This was accomplished by applying nonlinear curve fitting to dat a on the cumulative dose requirement during the initial 90-min period after bolus administration of rocuronium. Patient characteristics and controller performance, i.e., the ability of the controller to maintai n the neuromuscular block constant at the set-point, did not differ si gnificantly between the groups. I(ss) values calculated per lean body mass were 0.64 +/- 0.22, 0.60 +/- 0.15, 0.61 +/- 0.21, 0.67 +/- 0.31, 0.63 +/- 0.15, and 0.39 +/- 0.17 mg.kg-1.h-1 in the etomidate, fentany l, midazolam, propofol, thiopental, and isoflurane groups, respectivel y. The isoflurane group had a lower steady-state rate of infusion of r ocuronium than the other five groups (P < 0.05). Compared to intraveno us anesthetics, etomidate, fentanyl, midazolam, propofol, or thiopenta l, isoflurane reduced the infusion requirement of rocuronium by 35%-40 %.