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: ) under ultrasound-guided STB. 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: of 0.25% ropivacaine for ultrasound-guided STB was estimated to be 9.1 mL (95% CI: 8.3-9.9 mL). No patient developed severe bradycardia (heart rate ≤40 bpm) attributable to dexmedetomidine sedation. Conclusion: of 0.25% ropivacaine required to achieve surgical anesthesia for ultrasound-guided STB under dexmedetomidine sedation is 9.1 mL. Trial Registration Number: ChiCTR2200059042.