TACTILE EVALUATION OF TRAIN-OF-FOUR COUNT AS AN INDICATOR OF RELIABILITY OF ANTAGONISM OF VECURONIUM-INDUCED OR ATRACURIUM-INDUCED NEUROMUSCULAR BLOCKADE

Recent evidence suggests that edrophonium is not the agent of choice to reverse profound neuromuscular blockade but remains an efficacious drug when the level of neuromuscular blockade to be antagonized is modest. We studied 90 healthy adults in an attempt to address the questions: 1) How much variability in such neuromuscular parameters as single twitch height and the train-of-four (TOF) fade ratio (T4/T1) exist when the TOF count first returns to four palpable responses? 2) Is edrophonium a reliable antagonist at this measured point of recovery? 3) What is the optimal dose of edrophonium needed to produce prompt (< 10 min) and satisfactory (T4/T1 > 0.7) reversal when the fourth response of the thumb to indirect TOF stimulation just becomes palpable? Patients were given a bolus atracurium or vecuronium (n = 45 in each group) followed by an iv infusion sufficient to maintain single twitch as measured by electromyography at 10-15% of control values. At the end of surgery, the infusion was terminated and spontaneous recovery was allowed to begin. Once the tactile TOF count was four, edrophonium 0.3, 0.5, or 0.75 mg/kg was administered. At a count-of-four the first twitch averaged 37% of control (+/- 8.5% standard deviation; pooled data from all groups) and the mean T4/T1 ratio was 0.14 +/- 0.049. After atracurium neuromuscular blockade, edrophonium 0.3 mg/kg produced adequate antagonism in 10 min. At this time the mean T4/T1 ratio was 0.79 +/- 0.07 and the lowest observed value was 0.67. Increasing the edrophonium dose to 0.75 mg/kg accelerated recovery by 4-5 min. At a TOF count-of-four after vecuronium administration, edrophonium 0.75 mg/kg produced similar results. However, 0.3 and 0.5 mg/kg of edrophonium resulted in less consistent reversal of vecuronium. In these groups, 2 and 3 individuals respectively had T4/T1 ratios < 0.60 at 10 min postantagonism despite mean values of 0.70. For reversal of residual vecuronium blockade at the point of return of the TOF count to four, therefore, the recommended dose of edrophonium is 0.75 mg/kg. Under similar conditions after atracurium, as little as 0.3 mg/kg of edrophonium will produce reliable antagonism if 10 min is allowed for recovery.