Postoperative extradural analgesia with morphine and ropivacaine. A double-blind comparison between placebo and ropivacaine 10 mg/h or 16 mg/h.

BACKGROUND: Some controversy exists in the literature on the benefit of epidurals compared to patient-controlled intravenous analgesia (PCA). Also, the dose of ropivacaine for epidural analgesia when combined with morphine remains uncertain. The aim of this study was to compare the epidural vs. PCA technique and high-dose vs. low-dose ropivacaine combined with morphine during knee replacement surgery.

METHODS: In this prospective, randomized, double-blind study, postoperative pain relief with a combination of epidural ropivacaine (Group L: 10 mg h-1, Group H: 16 mg h-1) and morphine (0.16 mg h-1) was evaluated in 30 patients. A placebo group (Group PL) of 15 patients having PCA morphine served as the control. Visual analog pain (VAS), morphine consumption, sensory and motor block and side-effects were recorded during 48 h.

RESULTS: VAS scores at rest were significantly lower in Groups L and H compared to Group PL. On movement, Group H had lower VAS scores than Group PL during 3-27 h (P<0.05) and Group L during 4-9 h (P<0.05), while Group L had lower a VAS than Group PL during 9-18 h (P<0.05). Morphine consumption after 48 h was greater in Group PL (64.6+/-36.3 mg) vs. Group L (23.3+/-33.9 mg) (P<0.001) and Group H (4.3+/-9.6 mg) (P<0.0001). Mild motor block was seen in Group H in 20% and 14% patients at 24 h and 48 h, respectively, but time to mobilization was similar between the groups. Pruritus was more common in the ropivacaine groups (P<0.05).

CONCLUSION: Lumbar epidural analgesia using a combination of ropivacaine (16 mg h-1) and morphine (0.16 mg h-1) provides superior analgesia compared to the PCA technique or ropivacaine (10 mg h-1) and morphine (0.16 mg h-1). Although this resulted in a mild motor block during the first 12 h, patient mobilization was similar in all groups.