Morphine infusion after pediatric cardiac surgery.

After cardiac surgery, 44 children received a continuous iv infusion of morphine sulfate at 10 to 30 micrograms/kg X h. During weaning from assisted ventilation and during spontaneous ventilation serum morphine levels less than 30 ng/ml were not associated with elevated PaCO2. Five extubated patients breathed spontaneously, and 35 patients were weaned from assisted to spontaneous ventilation with normal PaCO2 while receiving morphine by infusion, indicating that morphine did not interfere with spontaneous ventilation. In 12 older children who gave verbal pain scores, pain was relieved at serum morphine levels above 12 ng/ml.