Cumulation and reversal with prolonged infusions of atracurium and vecuronium

Abstract

A randomized, doubleblind study was undertaken to compare the tendencies for cumulation, and reversal characteristics of atracurium (ATR) and vecuronium (VEC) when administered by continuous infusionfor long surgical procedures under balanced anaesthesia. Eligible subjects were between 50 and 75 yr of age and were free of neuromuscular disease. Patients in the ATR group (n = 25) received a loading dose of atracurium 0.25 mg· kg-1, followed by an infusion initially set at 5.0 μg · kg-1 · min-1. In the VEC group (n = 25) patients received a loading dose of vecuronium 0.05 mg · kg-1, followed by an infusion at 1.0 μg · kg-1 · min-1. During surgery, the infusions of both ATR and VEC were titrated in increments or decrements of 12.5% to maintain first twitch (TI) suppression of 90-95%. Neuromuscular block was measured by recording the integrated evoked electromyographic response (EMG) of the first dorsal interosseous muscle in response to supramaximal TOF stimuli on the ulnar nerve. The durations of infusion were similar for the two groups (164 ± 42 and 183 ± 67 min for ATR and VEC, respectively). The infusion rates of ATR (mean ± SD) remained between 4.0 ± 0.7 and 5.0 ± 1.0 μg · kg- 1 · min- 1 throughout the study period. In contrast, a progressive decrease (P < 0.05) in the infusion rate of VEC, from 1.0 to 0.47 ± 0.13 μg · kg-1 · min-1, was observed during the study period. The number of adjustments required to maintain 90-95% TI suppression decreased between the second and fourth hours of administration, but were similar at corresponding times when comparing the two groups. The times to recover to a TOF ratio >70% following reversal with neostigmine 40 μg· kg-1 and atropine 15 μg · kg-1 were also similar for the two groups (13.4 ± 4.9 and 14.4 ± 8.0 min for ATR and VEC, respectively). We conclude that a constant infusion of vecuronium adjusted to maintain TI suppression of 90-95% results in cumulation which is manifest after the second hour of administration. In contrast, atracurium shows little tendency for cumulation during infusions lasting between two and five hours. When titrated according to individual patient response, infusions of both atracurium and vecuronium are characterized by their ease of administration and their ability to be readily reversed with appropriate doses of neostigmine. © 1992 Canadian Anesthesiologists.