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

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.