A background infusion of morphine enhances patient-controlled analgesia after cardiac surgery.

PURPOSE We compared the efficacy of patient-controlled analgesia (PCA), with or without a background infusion of morphine, on postoperative pain relief in patients extubated in the operating room after coronary artery bypass grafting (CABG) surgery. METHODS With Faculty Ethics approval, 60 consenting adults undergoing elective coronary artery surgery were randomly assigned to receive either morphine PCA alone (group PCA-A, n = 30) or morphine PCA plus a background infusion (group PCA-B, n = 30) for 24 hr postoperatively. Pain scores with verbal rating scale (VRS; from 0 to 10) at rest, sedation scores, morphine consumption and delivery/demand ratios were assessed at zero, one, two, four, six, 12 and 24 hr after surgery. Hemodynamic variables and arterial blood gases were also recorded in the same periods. RESULTS Sedation scores in the two groups were similar. At all study periods after the first postoperative hour, VRS remained below 5 in both groups. Pain scores were significantly lower in the background infusion group, which also had greater cumulative morphine consumption (61.7 +/- 10.9 mg vs 38.5 +/- 16.2 mg). There were no episodes of hypoxemia or hypertension. CONCLUSION Morphine PCA effectively controlled postoperative pain after cardiac surgery. The addition of a background infusion of morphine enhanced analgesia and increased morphine consumption.