CONTINUOUS INFUSIONS OF ATRACURIUM AND VECURONIUM, COMPARED WITH INTERMITTENT BOLUSES OF PANCURONIUM - DOSE REQUIREMENTS AND REVERSAL

This study was designed to determine the effect of prolonged infusion on the ease of reversal of atracurium and vecuronium, and whether factors which potentiate the block delayed reversal In phase one, 40 patients were randomized (double blind) to determine the steady state conditions for atracurium and vecuronium. Fourteen atracurium patients and 17 vecuronium patients were evaluable. The unblinded second phase involved the steady state conditions using halothane or isoflurane and atracurium infusions. The infusion required for 95% twitch depression (TD95) for atracurium was 7.6 +/- 1.1 mug . kg-1 . min-1. The requirement for vecuronium changes with time: TD95 at 30 min was 1.01 +/- 0.16, at 60 min 0.89 +/- 0.12 and after 90 min 0.85 +/- 0.17 mug . kg-1 . min-1 (P < 0.05). The mean TD95 was 0.94 +/- 0.23 mug . kg-1 . min-1. Multivariate regression analysis of the infusion data revealed a vecuronium model predicting TD95 by the duration of infusion (P < 0.05) and weight (P = 0.05). Atracurium TD95 was predicted by age (P = 0.05). The addition of an inhalation agent to atracurium reduced the infusion rate by 2.01 +/- 0.28 mug . kg-1 . min-1 (P = 0.0001) for each increase in MAC. The mean reversal times for atracurium with three different anaesthetics and for vecuronium were not different. Reversal of pancuronium blockade, from less profound twitch depression (86.4 vs 95%) took twice as long as for atracurium and vecuronium for which the following predictors were identified: age, weight, duration of infusion, level of blockade, and type of anaesthetic, using a stepwise regression model For vecuronium: age (coeff 2.84 +/- 0.51 P = 0.0001) and duration of infusion (coeff 0.12 +/- 0.02 P = 0.0002) were significant predictors. Age was the only predictor of the time to reverse block after atracurium blockade with all types of anaesthetic (P = 0.05).