Plasma Concentrations of Morphine during Postoperative Pain Control

Background: Morphine has been commonly used for postoperative pain control. We measured plasma concentrations of morphine and compared the efficacy and safety of continuous epidural analgesia (CEA) using morphinebupivacaine with intravenous patient controlled analgesia (IV-PCA) with morphine for 48 hrs after the end of the operation. Methods: Nineteen patients undergoing Mile's operation were assigned to receive a morphine loading dose of 5 mg followed by IV-PCA with 0.1% morphine (IV-PCA group, n = 9) or a morphine loading dose of 2 mg and 0.125% bupivacaine 10 ml, followed by CEA with 0.004% morphine and 0.075% bupivacaine at a rate of 5 ml/hr (CEA group, n = 10). The plasma concentrations of morphine were measured and visual analog scales (VAS) for pain were recorded at 1, 6, 12, 24, and 48 hr postoperatively and the effects on respiration and any other side effects were noted. Results: The mean maximal and minimal levels of plasma morphine were $40.2{\pm}21.2\;ng/ml$ and $23.4{\pm}9.7\;ng/ml$ for the IV-PCA group and $11.8{\pm}3.5\;ng/ml$ and $8.2{\pm}1.9\;ng/ml$ for the CEA group, respectively. Resting and dynamic pain scores were significantly lower in the CEA group than in the IV-PCA group. There were no significant differences for the effects on respiration and for any side effects between the two groups. Conclusions: We evaluated plasma concentrations of morphine with CEA using morphine-bupivacaine and IV-PCA using morphine for the postoperative pain control. The CEA group had better postoperative analgesia than that of the IV-PCA group and the incidence of side effects were not significantly different between the two groups.