Is the combination of morphine with ketamine better than morphine alone for postoperative intravenous patient-controlled analgesia?

BACKGROUND: The addition of ketamine to morphine for patient-controlled analgesia (PCA) is supported by previous basic and clinical research, but has been challenged by subsequent negative studies. Important limitations of previous studies are the low number of patients analyzed, the use of morphine-ketamine combinations that may not the optimal, and that not all the relevant outcomes have been analyzed. In this study, we compared the combination of morphine and ketamine with morphine alone for postoperative PCA in large patient groups. We used a morphine-ketamine combination identified by an optimization procedure in our previous study. METHODS: After major elective orthopedic surgery, 352 patients received either PCA with morphine bolus 1.5 mg (Group M, n = 176) or a bolus of morphine plus ketamine 1.5 mg each (Group MK, n = 176) in a randomized, double-blind fashion. Unsatisfactory treatment was defined as the occurrence of either inadequate analgesia or unacceptable side effects. In addition, total consumption of PCA drugs, duration of PCA use, direct medical costs, and number of patients with chronic postoperative pain 3 and 6 mo after operation were recorded. RESULTS: The incidence of unsatisfactory treatment was 33.0% in Group M and 36.9% in Group MK (P = 0.50). No significant differences were found between the groups with respect to secondary end points. CONCLUSIONS: Small-dose ketamine combined with morphine for PCA provides no benefit to patients undergoing major orthopedic surgery and cannot be recommended for routine use.