Sevoflurane exposure time and the neuromuscular blocking effect of vecuronium

To determine the effect of sevoflurane exposure time on the duration of vecuronium neuromuscular blockade.

In 40 adult patients anesthesia was induced with 1.5-2 mg x kg(-1) propofol and 3-5 microg x kg(-1) fentanyl and the trachea was intubated without the aid of muscle relaxant. Patients were randomized into four groups of 10. In group 1, 0.05 mg x kg(-1) vecuronium was administered with N2O and anesthesia was maintained by propofol infusion and fentanyl. Vecuronium was administered with sevoflurane 2% in 30 patients, commencing at the same time (group 2) and at 30, and 60 min after sevoflurane (groups 3, 4). Adductor pollicis force of contraction to train-of-four ulnar nerve stimulation was recorded. Times from vecuronium injection to 95%, maximal block, and recovery times to 25% recovery were recorded.

There were no differences in times to 95% and maximal block in the four groups. Recovery times were longer in groups 3 and 4 than in groups 2 and 1 (P < 0.01). Times to 5% recovery were 15.0 +/- 3.7, 17.8 +/- 4.8, 28.2 +/- 9.9, and 29.5 +/- 9.5, and to 25% recovery were 22.3 +/- 5.2, 27.2 +/- 6.4, 42.3 +/- 16.3, and 50.5 +/- 16.4 in groups 1, 2, 3, and 4 respectively. No differences were found between group 1 and group 2 nor between group 3 and group 4.

Sevoflurane produced time-dependent potentiation of vecuronium. After 30 min exposure, 25% recovery was prolonged by 89% and after 60 min by more than 100% compared with the control group.