Abstract
BACKGROUND: Postoperative pain management is essential after video-assisted thoracoscopic surgery (VATS). The rhomboid intercostal and sub-serratus (RISS) block is effective in providing analgesia. This study aims to determine the minimum effective concentration (MEC) of ropivacaine for ultrasound-guided RISS block in patients undergoing VATS, thereby optimizing the analgesia protocol and enhancing its clinical significance. METHODS: The biased coin design sequential method and isotonic regression were used. The ropivacaine initial concentration was 0.25% with a gradient of 0.025%. If the previous patient had a negative block, the concentration for the next patient would increase by 0.025%. If positive, the concentration would be adjusted based on biased coin randomization: an 11% chance of reducing it by 0.025% and an 89% chance of keeping it unchanged. MEC(90) was calculated using isotonic regression with 95% confidence intervals (CI). RESULTS: A total of 49 patients were included in the analysis. The MEC(90) of 40mL ropivacaine for RISS block in VATS was 0.220% (95% CI, 0.198 to 0.260%), the MEC(95) was 0.248% (95% CI, 0.223 to 0.338%) and the MEC(99) was 0.270% (95% CI, 0.261 to 0.351%). There was a negative correlation between ropivacaine concentration and VAS(pain) at 0h, 0.5h, and 6h after surgery and the time of initial analgesia (r = -0.396, -0.594, -0.309, 0.363; P = 0.005, 0.001, 0.031, 0.01). No significant correlation was observed between the VAS(pain) at 12h and 24h after surgery and analgesia consumption (r = -0.184, -0.165; P = 0.205, 0.256). CONCLUSION: The MEC(90) of 40 mL ropivacaine for RISS block was 0.220%. While the MEC(95) was 0.248% and the MEC(99) was 0.270%.