POTENCY AND TIME-COURSE OF ACTION OF ROCURONIUM DURING DESFLURANE ANDISOFLURANE ANESTHESIA

We have studied the potency and onset and duration of action of rocuro nium in patients anaesthetized with 1 MAC of desflurane or isoflurane (in 66% nitrous oxide). Potency was estimated using the single bolus d ose technique. Neuromuscular block was measured by stimulation of the ulnar nerve and recording the force of contraction of the adductor pol licis muscle. The ED(50) and ED(95) of rocuronium were estimated as 13 8 (95% confidence limits 117-162) mu g kg(-1) and 281 (241-328) mu g k g(-1), and 126 (105-151) mu g kg(-1) and 283 (236-339) mu g kg(-1) dur ing desflurane and isoflurane anaesthesia, respectively. The mean time s to onset of maximum block after rocuronium 0.6 mg kg(-1) were 1.0 (S D 0.10) min and 1.1 (0.15) min, respectively, during anaesthesia with desflurane and isoflurane. The respective times to recovery of T1 (the first response in the train-of-four (TOF) stimulation) to 25% and 90% were 36 (8.3) min and 54 (15.4) min during desflurane anaesthesia and 31 (8.2) min and 45 (12.7) min during isoflurane anaesthesia. The tim es to recovery of the TOF ratio to 0.7 were 55 (13.4) min and 52 (16.3 ) min and the 25-75% recovery indices 14 (5.3) min and 10 (3.2) min, r espectively, in the desflurane and isoflurane groups. There were no di fferences in the estimated potency or onset of action of rocuronium du ring desflurane and isoflurane anaesthesia. However, duration of actio n tended to be longer during desflurane anaesthesia although only the differences in times to TOF ratio of 0.7 and the recovery indices were close to being significantly different (P=0.0503 and 0.0560).