Ventilatory depression during and after infusion of alfentanil in man

Sixteen fit young patients undergoing body surface surgery received an infusion of alfentanil 50 or 100 micrograms kg-1 h-1 to supplement nitrous oxide anaesthesia. The alfentanil infusion was continued for 2 h after operation at the slower rate of 20 micrograms kg-1 h-1. The intraoperative infusions provided satisfactory conditions for anaesthesia. The infusion after operation provided adequate analgesia at a cost of depression of carbon dioxide responsiveness to 50% of its value before operation, but only moderate effects on minute volume and PaCO2. Plasma alfentanil concentration during the postoperative infusion was 108 +/- 37 ng ml-1 (mean +/- SD).