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 (MEV9 0) 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 MEV9 0 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 MEV9 0 of 0.25% ropivacaine required to achieve surgical anesthesia for ultrasound-guided STB under dexmedetomidine sedation is 9.1 mL.

TRIAL REGISTRATION NUMBER: ChiCTR2200059042.