Continuous epicapsular ropivacaine 0.3% infusion after minimally invasive hip arthroplasty: a prospective, randomized, double-blinded, placebo-controlled study comparing continuous wound infusion with morphine patient-controlled analgesia.

BACKGROUND: In this study, we investigated the impact of a continuous wound infusion with ropivacaine 0.3% on pain and morphine consumption after minimally invasive hip arthroplasty.

METHODS: Seventy-six consecutive patients scheduled for elective minimally invasive hip replacement using spinal anesthesia were prospectively included in this double-blind study. Epicapsular placement of a 15-cm fenestrated catheter was performed by the surgeon. Patients were randomized to receive either 20 mL ropivacaine 0.3% (R-group) or 20 mL NaCl 0.9% (P-group) applied into the wound as a bolus before wound closure. A continuous infusion of either ropivacaine 0.3% or placebo was then infused at 8 mL/h for 48 hours after surgery with an elastomeric pump. Morphine IV-patient-controlled analgesia was offered to all patients. Morphine consumption, pain at rest and with motion, and total and unbound ropivacaine plasma concentration were recorded during the 48-hour study period. Postoperative follow-up was performed at 3 months.

RESULTS: Demographic and surgical data were similar in both groups. Mean morphine consumption was significantly lower in the R-group than in the P-group during the first 48 postoperative hours: 45.4 ± 9.5 vs 69.7 ± 9.6 (P < 0.0001). There was a mean reduction of 14.4 mg for the first 24 postoperative hours (95% confidence interval [CI] 12.6 to 16.1) and 20.8 mg for the next 24 hours (95% CI 19.1 to 22.4). Pain scores at rest and with motion were lower in the R-group (P < 0.0001). Mean patient satisfaction increased 22.7% from baseline (CI 95% 15.9 to 29.6) in the R-group. Total and unbound ropivacaine plasma concentrations were below toxic levels in the R-group. The free ropivacaine concentration was 0.14 and 0.11 μgmol/L at T(24) and T(48), respectively, in the R-group. At 3 months postoperatively, hip pain and analgesic consumption were similar, but a significant reduction in wound discomfort to touch (31.2; 95% CI 27.7 to 34.7) and pressure (24; 95% CI 20.1 to 27.9) was observed in the R-group (P < 0.0001).

CONCLUSIONS: Continuous epicapsular wound infusion with ropivacaine 0.3% after minimally invasive hip replacement is an efficient technique for reducing morphine consumption and improving the quality of postoperative analgesia. The beneficial effects of this technique are still present 3 months after surgery.