Postoperative respiratory effects of morphine and halothane anesthesia: a study in patients undergoing cardiac surgery.

Lung volumes, deadspace, ventilation, and ventilatory response to CO2 challenge were studied on the day before and for the first three days after corrective cardiac surgery. Ten patients underwent coronary artery bypass grafting and ten patients had mitral valve prostheses inserted. Half of the patients in each group received halothane as the major anesthetic, and the other half received morphine sulfate (1-2 mg/kg). Mitral valve-replacement patients anesthetized with morphine showed lower CO2 sensitivity on the first postoperative day than those who received halothane. Patients who had coronary artery bypass grafts tended to hyperventilate during the postoperative period, but this did not occur on the first postoperative day in those who received morphine anesthesia. Respiratory rate was always higher postoperatively, most markedly in patients who receivedhalothane for coronary artery bypass grafts. Vital capacity was diminished by 67 per cent in all groups postoperatively. VD/VT tended to increase during the first and second postoperative days and then decrease toward control values on the third postoperative day in all groups except valve-replacement patients who received morphine. Morphine anesthesia may increase the period of mechanical ventilation necessary after cardiac surgery partly as a result of impaired CO2 sensitivity.