Onset of neuromuscular block during total intravenous anaesthesia: effects of ketamine compared with alfentanil.

Anaesthesia was induced in 30 ASA I patients by propofol titrated at 100 mg min-1 to loss of verbal contact, and maintained by infusion of propofol at 10 mg kg-1 h-1 with 100% oxygen. According to randomization, either alfentanil 30 micrograms kg-1 ketamine 1.5 mg kg-1, or 0.9% sodium chloride was injected over 20 s, followed 1 min later by vecuronium 0.08 mg kg-1. Mean arterial pressure and heart rate were measured before and after induction, and 1 and 2 min after analgesic or saline. Onset of neuromuscular block was measured by the evoked hypothenar electromyographic response to train-of-four supra-maximal stimuli at 0.1 Hz. There were significant haemodynamic differences between groups, but mean (SD) times to reduction of T1/control ratios below 95% were 114 (28.0), 106 (19.0) and 128 (34.3) s (P = 0.2, ANOVA). Supplementation of propofol anaesthesia with alfentanil or ketamine does not appear to influence the onset time of vecuronium.