FACTORS AFFECTING NEOSTIGMINE REVERSAL OF VECURONIUM BLOCK DURING SEVOFLURANE ANESTHESIA

We examined the influence of the concentration of sevoflurane and the degree of muscle block at the time of reversal on the activity of neos tigmine. Ninety ASA 1-2 patients were anaesthetised with 0.2, 0.7 or 1 .2 MAC of sevoflurane (30 patients each) in 66% nitrous oxide in oxyge n. The electromyographic (EMG) response of the adductor digiti minimi was monitored at 20-s intervals after train-of-four stimulation of the ulnar nerve. The initial neuromuscular block was produced by vecuroni um 100 mu g.kg(-1). When the amplitude of the first response (T1) valu es had recovered to 10%, 25% or 30% of the control, neostigmine 40 mu g.kg(-1) was administered. The train-of-four ratio values were recorde d at 1-min intervals during the subsequent 15-min period. Higher end-t idal concentrations (p < 0.0001) and more pronounced block at the time of reversal (p < 0.0001) were associated with a delayed recovery in t he train-of-four ratio. In addition, the train-of-four ratio 15 min af ter neostigmine administration was more dependent on the sevoflurane c oncentration than on the degree of block present (p < 0.0001). These r esults confirm that neostigmine (40 mu g.kg(-1)) can reverse vecuroniu m-induced but not sevoflurane-induced neuromuscular block.