The effect of isoflurane versus balanced anesthesia on rocuronium's pharmacokinetics and infusion requirement

To compare the effects of two anesthetic techniques, balanced and isoflurane anesthesia, on the response to an intubating dose and an infusion of rocuronium, and on rocuronium's pharmacokinetics.

Randomized, open-label study.

A university-affiliated hospital.

Twenty-two healthy adults undergoing elective surgery.

The patients were anesthetized with a balanced technique (nitrous oxide, fentanyl, midazolam) or isoflurane (nitrous oxide, isoflurane 0.5-1.0%). Rocuronium was administered initially as a 500-micrograms/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.

Onset time and initial recovery after the bolus dose were similar for the two groups. Infusion requirements also were similar. Plasma clearance was greater during isoflurane than during balanced anesthesia (4.48 vs 3.49 ml/kg/min). Distribution clearances and volumes of distribution were similar for the two groups.

The similarity of response to an intubating dose and an infusion 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 rocuronium, in light of the similarity of infusion requirements, suggests that isoflurane potentiates rocuronium compared with balanced anesthesia.