Effective concentration of Ropivacaine for post-operative pain relief in Total knee replacement surgeries using ultra sound guided continuous femoral block – A randomized double blinded study

Abstract

Introduction: Postoperative pain in total knee replacement surgeries is severe and needs intense analgesia. Of various analgesic techniques available, continuous femoral nerve block is safe and associated with minimal side effects. Objectives: To compare the analgesic effect of various concentrations of ropivacaine using continuous femoral nerve block for post-operative pain relief in total knee replacement surgeries. Methods: 120 patients posted for elective total knee replacement (TKR) surgeries under American Society of Anesthesiologists (ASA) physical classification I or II, under spinal anaesthesia, were randomly allocated into four groups of 30 each. Group 1, 2, 3 and 4 received ropivacaine 0.12%, 0.16%, 0.20% and 0.25% respectively at 10 mL per hour infusion, by ultrasound-guided continuous femoral nerve block. Pain relief was assessed by visual analogue scale (VAS). Analgesic requirement in the post-operative period and hemodynamic changes compared between four groups. Results: There was no statistical difference in change in hemodynamics over time between all four groups. Analgesic requirement was significantly less and VAS score was significantly low in group 3 and group 4. Conclusion: In this study, the minimum effective concentration of ropivacaine when used for pain relief in continuous femoral block in total knee replacement surgeries is found to be 0.20%. Keywords: Analgesia; Knee replacement; Nerve block; Ropivacaine; Ultrasound