Quantitation of the enflurane-sparing effect of alfentanil during general surgery

The authors quantitated the enflurane-sparing effect of alfentanil during N2O/O2 anaesthesia in 50 patients undergoing body surface surgery and in 50 patients undergoing upper abdominal surgery. Patients were assigned to one of five treatment regimens (10 patients each group, double-blind administration) as follows: placebo bolus followed by placebo infusion (group I); or alfentanil bolus (30 micrograms kg-1) followed by infusion of placebo (group II) or alfentanil, at the rate of 10 (group III), 20 (group IV), or 40 (group V) micrograms kg-1 h-1. Anaesthesia was induced with thiopentone and vecuronium, and neuromuscular block was kept at 85-90% by continuous infusion of vecuronium. Increases in spontaneous electromyographic activity of neck muscles (NEMG) and in systolic blood pressure (SBP) served as criteria of inadequate anaesthesia. When such increases occurred, enflurane was given in 0.2% steps (end-tidal concentration) of 5 min each, until the increases were suppressed. The relationship between increases in NEMG and increases in SBP was inconsistent: only 10% of the increases occurred simultaneously. With alfentanil, the consumption of enflurane decreased by as much as 70% (P < 0.001) during superficial surgery and 50% (P < 0.05) during abdominal surgery.