Effect of domperidone on the ventilatory response to transient hyperoxia in patients anaesthetized with isoflurane

We have studied the ventilatory responses to transient hyperoxia in two groups of patients (n = 10) anaesthetized with isoflurane (0.3 MAC); patients were allocated randomly to receive either domperidone or placebo orally before anaesthesia. In each patient, five two-breath oxygen tests were averaged and minute ventilation (VEinst) or mean inspiratory flow rate (VT/TI) for each post-test breath was compared with the mean values for these variables during baseline ventilation. A decrease to less than the 95% confidence limits of mean baseline values was considered a definite response. According to this definition, transient hyperoxia decreased VEinst in nine of 10 patients in the placebo group and in all patients in the domperidone group. Similar changes occurred in VT/TI, with eight of 10 definite responses in the placebo group and 10 of 10 in the domperidone group. Compared with placebo, in the domperidone group there were larger changes in VEinst (0.30 vs 0.55 litre min-1 (P = 0.05) and VT/TI (8.5 vs 26.6 ml s-1 (P = 0.02)) from respective baselines. Peripheral chemoreceptors appeared to be active during isoflurane anaesthesia and domperidone pretreatment enhanced this activity by increasing respiratory drive.