Determination of the Optimal Volume of 0.5% Ropivacaine in Single-injection Retroclavicular Brachial Plexus Block for Arthroscopic Shoulder Surgery: A Phase I/II Trial

BACKGROUND: A brachial plexus block plays an important role in providing perioperative analgesia for shoulder surgery; however, the inherent risk of phrenic nerve block and resulting hemidiaphragmatic paralysis may limit its use in patients with compromised pulmonary function. This study aimed to evaluate the safety, efficacy, maximum tolerated volume, and optimal biologic volume of 0.5% ropivacaine used in a single-injection retroclavicular brachial plexus block for arthroscopic shoulder surgery. METHODS: In this seamless single-arm exploratory phase I/II trial, a novel Bayesian optimal interval design was used to guide volume escalation for determination of the maximum tolerated volume, followed by sequential volume expansion using Bayesian optimal phase 2 design to establish the optimal biologic volume. Fifty-four patients who underwent arthroscopic shoulder surgery received a single-injection retroclavicular brachial plexus block with 0.5% ropivacaine ranging from 15 to 40 ml. The primary outcomes were complete or partial hemidiaphragmatic paralysis in phase I, measured using ultrasound 30 min after block completion, and the block success in phase II, defined as achieving a total sensorimotor score 12 points or greater and the total sensory score 3 points or greater, measured through manual sensorimotor testing. RESULTS: The maximum tolerated volume for the single-injection retroclavicular brachial plexus block was determined to be 35 ml of 0.5% ropivacaine, with a hemidiaphragmatic paralysis rate of 0.09 (95% credible interval, 0 to 0.29). The optimal biologic volume was found to be 25 ml, with a block success rate of 1.0 (95% credible interval, 0.95 to 1.0) and a negligible hemidiaphragmatic paralysis rate of 0.01 (95% credible interval, 0 to 0.06). CONCLUSIONS: A single-injection retroclavicular brachial plexus block using 25 ml of 0.5% ropivacaine produced consistent block success with a minimal hemidiaphragmatic paralysis rate, suggesting the need for further studies to confirm this result in arthroscopic shoulder surgery.