Vecuronium infusion dose requirements during fentanyl and halothane anesthesia in humans.

Steady-state infusion rate requirements of vecuronium were determined in 29 patients during either halothane-nitrous oxide or fentanyl-nitrous oxide anesthesia at different levels of neuromuscular block. During N2O-halothane anesthesia (end-tidal concentration, 0.5%), the infusion rate necessary for a steady-state (defined as unchanging twitch height and infusion rate for at least 20 min) 50% depression of twitch force was 28.8 +/- 5.4 (mean +/- SD) (n = 8) and 47.6 +/- 9.7 micrograms . kg-1 . hr-1 (n = 6) at 90% reduction of twitch force. During N2O-fentanyl anesthesia, the steady-state infusion rate required for 50 and 90% decrease of twitch force was 56.3 +/- 20.0 (n = 9) and 74.8 +/- 16.0 micrograms . kg-1 . hr-1 (n = 6), respectively. The variances of vecuronium steady-state infusion dose requirements were smaller in the halothane groups than in the fentanyl anesthesia groups. The steady-state vecuronium infusion dose requirements during fentanyl anesthesia were greater than the mean infusion dose requirements during halothane anesthesia at equivalent levels of twitch depression.