Optimal effective concentration of ropivacaine for postoperative analgesia by single-shot femoral–sciatic nerve block in outpatient knee arthroscopy

Abstract

Objective To compare analgesic and mobility effects of different ropivacaine concentrations in femoral–sciatic nerve block, for postoperative analgesia in knee arthroscopy. Methods Outpatients (American Society of Anesthesiologists physical classification status of I or II), scheduled for elective knee arthroscopy, were randomly allocated to one of seven groups, prospectively investigating different concentrations of ropivacaine (0.12%; 0.14%; 0.16%; 0.18%; 0.20%; 0.22% or 0.50%), for ultrasound-guided femoral–sciatic nerve block procedures for postoperative analgesia. Visual analogue scale (VAS) pain scores and motor block evaluation scales were observed at 4, 8, 16 and 24 h postsurgery. Results In total, 105 patients were enrolled; results were analysed for 103. VAS scores for the 0.12%, 0.14% and 0.16% groups were significantly different from the 0.50% group. There were no significant differences between the 0.18%, 0.20%, 0.22% and 0.50% groups: half maximal effective concentrations and 95% maximal effective concentrations of ropivacaine were 0.158 (95% confidence intervals [CI] 0.149, 0.167) and 0.198 (95% CI 0.186, 0.221), respectively. Rates of motor blockade (Bromage score or hip motor function scale > 0) were significantly different between the 0.50% group and all other ropivacaine doses. Conclusion The 0.20% ropivacaine dose for femoral–sciatic nerve block in knee arthroscopy provided satisfactory postoperative analgesia, while preserving ability of motion.