Minimum Effective Volume of 0.25% Ropivacaine for Ultrasound-Guided Superior Trunk Block with Dexmedetomidine Sedation in Shoulder Arthroscopy: A Biased Coin Up-and-Down Trial.

Background: Although interscalene brachial plexus block (ISB) remains the gold standard for shoulder arthroscopy, it is associated with a high incidence of hemidiaphragmatic paralysis (HDP). The superior trunk block (STB) offers comparable analgesia with a significantly reduced risk of HDP; however, the optimal local anesthetic dose for surgical anesthesia when STB is used alone has not been established. This study aimed to determine the minimum effective volume of 0.25% ropivacaine required to achieve surgical anesthesia in 90% of patients (MEV Methods: We employed a biased coin design up-and-down method (BCD-UDM). Starting from an initial volume of 5 mL, the dose for each subsequent patient was determined by the previous patient's outcome: failure triggered a 2 mL increase, while success led to random assignment between a 2 mL decrease (11% probability) or the same volume (89% probability). Block success was defined as a composite sensory score ≥9 at 30 minutes and completion of surgery under STB with dexmedetomidine sedation (loading dose 0.8 μg/kg over 15 min before incision, followed by a maintenance infusion of 0.1-0.5 μg/kg/h), without conversion to general anesthesia. Results: A total of 52 patients were included. Using isotonic regression with bootstrapped confidence intervals, the MEV Conclusion: The MEV Trial Registration Number: ChiCTR2200059042.