Enflurane Requirement and Ventilatory Response to Carbon Dioxide during Lidocaine Infusion in Dogs

Abstract
Arterial plasma lidocaine concentrations of 1-3.5 .mu.g/ml produced dose-related decreases in enflurane requirement (MAC) ranging from 15-37% in dogs. The ventilatory responses to CO at comparable depths of anesthesia with enflurane alone and the enflurane-lidocaine combination were measured in each animal and compared. With both anesthetic regimens there were increases in resting arterial CO2 tension (mean maximal increase = 18 torr) and a 69% decrease in the slope of the ventilatory response as depth of anesthesia increased. The effect of the drug interaction appears to be additive, since the ventilatory depression produced by the enflurance-lidocaine combination was no greater than that produced by enflurane alone at equivalent levels of anesthesia.