Minimum Effective Concentration of Ropivacaine for Ultrasound-Guided RISS Block in VATS: A Biased Coin Design Approach.

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 was calculated using isotonic regression with 95% confidence intervals (CI).

RESULTS

A total of 49 patients were included in the analysis. The MEC of 40mL ropivacaine for RISS block in VATS was 0.220% (95% CI, 0.198 to 0.260%), the MEC was 0.248% (95% CI, 0.223 to 0.338%) and the MEC was 0.270% (95% CI, 0.261 to 0.351%). There was a negative correlation between ropivacaine concentration and VAS at 0h, 0.5h, and 6h after surgery and the time of initial analgesia (r = -0.396, -0.594, -0.309, 0.363; = 0.005, 0.001, 0.031, 0.01). No significant correlation was observed between the VAS at 12h and 24h after surgery and analgesia consumption (r = -0.184, -0.165; = 0.205, 0.256).

CONCLUSION

The MEC of 40 mL ropivacaine for RISS block was 0.220%. While the MEC was 0.248% and the MEC was 0.270%.