THE EFFECT OF ISOFLURANE VERSUS BALANCED ANESTHESIA ON ROCURONIUMS PHARMACOKINETICS AND INFUSION REQUIREMENT

Study Objective. To compare the effects of two anesthetic techniques, balanced and isoflurane anesthesia, on the response to an intubating d ose and an infusion of rocuronium, and on rocuronium's pharmacokinetic s. Design. Randomized, open-label study. Setting. A university-affilia ted hospital. Patients. Twenty-two healthy adults undergoing elective surgery. Interventions. The patients were anesthetized with a balanced technique (nitrous oxide, fentanyl, midazolam) or isoflurane (nitrous oxide, isoflurane O.5-1.0%). Rocuronium was administered initially as a 500-mu g/kg bolus, then by infusion to maintain approximately 86-94 % depression of twitch tension. Plasma samples to determine rocuronium concentrations were obtained before, during, and after the infusion. Pharmacokinetics were determined using a population-based approach. Me asurements and Main Results. Onset time and initial recovery after the bolus dose were similar for the two groups. Infusion requirements als o were similar. Plasma clearance was greater during isoflurane than du ring balanced anesthesia (4.48 vs 3.49 ml/kg/min). Distribution cleara nces and volumes of distribution were similar for the two groups. Conc lusions. The similarity of response to an intubating dose and an infus ion of rocuronium suggests that clinicians need not alter the dose or rate of rocuronium administration during isoflurane anesthesia with a of duration less than 1 hour. However, the greater clearance of rocuro nium, in light of the similarity of infusion requirements, suggests th at isoflurane potentiates rocuronium compared with balanced anesthesia .