Dependence of the adequacy of muscle relaxation on the degree of neuromuscular block and depth of enflurane anesthesia during abdominal surgery.

We studied the intensity of neuromuscular block that is adequate for surgical relaxation at different end-tidal levels of enflurane during N2O-O2-fentanyl anesthesia in 30 patients undergoing upper abdominal surgery. After induction of anesthesia with thiopental 4-6 mg/kg and vecuronium 0.07 mg/kg intravenously (i.v.), patients were randomly assigned to receive nitrous oxide-oxygen (2:1) and enflurane at 0.3% (Group I), 0.6% (Group II), or 1.2% (Group III) end-tidal level throughout anesthesia. The initial neuromuscular block was allowed to terminate and additional increments of 1 mg vecuronium were given when indicated by clinical signs or by spontaneous electromyography of neck muscles. In Group I additional vecuronium had to be given 62 times and in Groups II and III, 33, and 16 times, respectively. The mean (SD) neuromuscular block at the time of additional vecuronium was 75.9% +/- 20.7%, 62.5% +/- 20.1%, and 39.3% +/- 21.1% in Groups I to III, respectively. We conclude that there was a clear linear relationship between the end-tidal concentration of enflurane and the degree of neuromuscular block necessary to produce adequate surgical muscle relaxation (P < 0.001).