NEUROMUSCULAR EFFECTS OF ROCURONIUM DURING SEVOFLURANE, ISOFLURANE, AND INTRAVENOUS ANESTHESIA

The potency and time course of action of rocuronium were studied in pa tients anesthetized with 66% nitrous oxide in oxygen and 1.5 minimum a lveolar anesthetic concentration of sevoflurane or isoflurane, or a pr opofol infusion. Potency was estimated by using the single-bolus techn ique. Neuromuscular block was measured by stimulation of the ulnar ner ve and by recording the force of contraction of the adductor pollicis muscle. The mean (95% confidence limits) of the 50% and 95% effective doses were estimated to be 142 (129-157) and 265 (233-301) mu g/ kg, 1 65 (146-187) and 324 (265-396) mu g/kg, and 183 (163-207) and 398 (316 -502) mu g/kg during sevoflurane, isoflurane, and propofol anesthesia, respectively (P < 0.05 for sevoflurane versus propofol). The mean +/- SD times to onset of maximal block after rocuronium 0.6 mg/kg were 0. 96 +/- 0.16, 0.90 +/- 0.16, and 1.02 +/- 0.15 min during sevoflurane, isoflurane, and propofol anesthesia, respectively. The respective time s to recovery of the first response in the train-of-four (TOF) stimula tion (T1) to 25% and 90% were 45 +/- 13.1 and 83 +/- 29.3 min, 35 +/- 6.1 and 56 +/- 15.9 min, and 35 +/- 9.2 and 55 +/- 19.4 min. The times to recovery of the TOF ratio to 0.8 were 103 +/- 30.7, 69 +/- 20.4, a nd 62 +/- 21.1 min, and the 25%-75% recovery indices were 26 +/- 11.7, 12 +/- 5.0, and 14 +/- 6.9 min,respectively. There were no difference s among groups in the times for onset of action or to recovery of T1 t o 25%. However, the times for recovery of T1 to 90%, TOF ratio to 0.8, and recovery index in the sevoflurane group were all significantly lo nger compared with the other two groups (P < 0.05, < 0.01, and < 0.01, respectively). We conclude that the effects of rocuronium, especially duration of action, are significantly enhanced during sevoflurane com pared with isoflurane and propofol anesthesia. Implications: In routin e clinical use, the effects of rocuronium are enhanced by sevoflurane, in comparison with isoflurane and propofol anesthesia, and the recove ry is slower. Particular attention should be paid to monitoring of neu romuscular block during sevoflurane anesthesia.