Enhancement of the arrhythmogenic effect of hypercarbia by surgical stimulation during halothane anaesthesia in man.

Abstract

We studied the levels of hypercarbia necessary to induce ventricular extrasystoles in one group of six subjects anaesthetized with halothane 1.3 MAC and in another group of six subjects anaesthetized with a 1.3 MAC combination of halothane and nitrous oxide, both before and during elective surgical procedures. Hypercarbia was induced progressively by total rebreathing to a maximum Pvco 2 value of approximately 11.0 kPa (83 torr). Pvco 2 values at which ventricular extrasystoles were first observed were taken as the Pvco 2arrhythmic thresholds.During anaesthesia alone in both groups, Pvco 2 arrhythmic thresholds were achieved in only one of six subjects and the median Pvco 2 thresholds were therefore greater than 11.0 kPa (83 torr). During halothane anaesthesia with surgery, thresholds were observed in all subjects and the median value was 9.1 kPa(68 torr). During halothane-nitrous oxide with surgery, thresholds were identified in three of six subjects and the median was greater than 10.7 kPa (80 torr). The thresholds during halothane with surgery were significantly less than the threshold or maximum Pvco 2values observed in each of the other three states (p values <0.05). The results indicate that during halothane anaesthesia, surgical stimulation markedly enhances the arrhythmogenic effect of added carbon dioxide and that, in the presence of surgery, a nitrous oxide-halothane mixture is less sensitizing than an equi-potent dose of halothane alone.