Duration of analgesia is similar when 15, 20, 25 and 30 mL of ropivacaine 0.5% are administered via a femoral catheter

Abstract

Purpose: This dose-response study was designed to determine the most appropriate dose of ropivacaine 0.5% injected via an indwelling femoral catheter for perioperative peripheral analgesia for total knee replacement (TKR).

Methods: 84 patients were allocated randomly to four groups and received, via a femoral catheter, either 15, 20, 25 or 30 mL of ropivacaine 0.5% in a double-blind fashion. An anterior sciatic block with 20 mL bupivacaine 0.5% was also performed. The evolution of sensory block of femoral, obturator and lateral femoral cutaneous nerves and motor block of femoral nerve were tested every five minutes during the first 30 min. The percentage of patients with complete sensory block of both femoral and obturator nerves determined success rate. General anesthesia was then induced. After surgery, patient-controlled analgesia (PCA) with ropivacaine 0.2% was available via the femoral catheter. The interval between the initial injection and the first PCA administration determined duration of action.

Results: The duration of action was not different between the four solutions tested i.e., 534 +/- 379 min for 15 mL, 799 +/- 364 min for 20 mL, 624 +/- 342 min for 25 mL and 644 +/- 266 min for 30 mL. The percentage of patients with complete sensory femoral and obturator blocks was, respectively, 60%, 95%, 85% and 70% for 15, 20, 25 and 30 mL (P = 0.008/15 mL vs 20 mL).

Conclusion: Although there is no difference in duration of analgesia, because of better sensory spread, 20 mL of ropivacaine 0.5% appears to be the most appropriate dose for peripheral analgesia after TKR.