Continuous intravenous morphine infusion in postoperative newborn infants.

The efficacy and safety of morphine sulfate was evaluated in 20 neonates requiring surgery. Following surgery, each subject received an intravenous morphine loading dose (50 micrograms/kg) followed by a continuous infusion (15 micrograms/kg/hr) for a minimum of 24 hours. Heart rate, respiratory rate, and blood pressure were frequently monitored during therapy. Blood samples were obtained following surgery and during and after morphine therapy for analysis of serum morphine and beta-endorphin content. A 12-hour urine collection was obtained 12 hours following the start of the constant morphine infusion for analysis of morphine content. The mean (+/- SD) duration of morphine infusion was 34 +/- 15 hours and a steady-rate serum morphine concentration was 39 +/- 23 ng/ml. The respective serum morphine half-life, elimination rate, and volume of distribution were 6.6 +/- 2.9 hr, 0.126 +/- 0.056 hr-1, and 5.0 +/- 6.8 liters/kg. The mean percentage of unchanged morphine recovered in the urine was 39 +/- 19 of the dose administered over 12 hours. A significant reduction in serum beta-endorphin content was observed following the onset of morphine therapy. No adverse reports were noted that could be attributed to morphine therapy. Continuous morphine therapy appears to be effective in controlling neonatal postoperative pain, as suggested by subjective nursing observations and decreased serum beta-endorphin content.