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

Kai Wang,1,2,* Shuhan Zhang,1,* Zhaoyu Lv,1,* Wei Chen,1 Yonghua Li1 1Department of Anesthesiology, Second Affiliated Hospital of Naval Medical University (Shanghai Changzheng Hospital), Shanghai, People’s Republic of China; 2Department of Anesthesiology, Shanghai Donglei Brain Hospital, Shanghai, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yonghua Li, Email liyonghua1207@smmu.edu.cn Wei Chen, Email 123494311@qq.comBackground: 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 (MEV90) 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: A total of 52 patients were included. Using isotonic regression with bootstrapped confidence intervals, the MEV90 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: The MEV90 of 0.25% ropivacaine required to achieve surgical anesthesia for ultrasound-guided STB under dexmedetomidine sedation is 9.1 mL.Trial Registration Number: ChiCTR2200059042.Keywords: superior trunk block, shoulder arthroscopy, minimum effective volume, biased coin design