Effects of ultrasound-guided superior trunk block with different ropivacaine volumes on hemidiaphragmatic paralysis and analgesic efficacy in patients undergoing arthroscopic rotator cuff repair: a study protocol for a prospective randomized controlled trial {1a}

Effective management of acute pain after arthroscopic rotator cuff repair (ARCR) is pivotal for implementing Enhanced Recovery After Surgery (ERAS) protocols. The superior trunk block (STB)—a technique targeting the C5–C6 nerve roots that innervate the shoulder joint—is widely used for this purpose. However, the optimal balance between local anesthetic (LA) volume, its volume-related impact on phrenic nerve function, and analgesic efficacy remains poorly defined, underscoring the urgency to identify an evidence-based LA volume. This study aims to systematically evaluate the effects of 5 mL, 10 mL, and 15 mL of 0.4% ropivacaine for STB on hemidiaphragmatic paralysis (HDP) incidence (assessed via diaphragmatic excursion) and postoperative analgesic efficacy in patients undergoing ARCR, with the goal of generating actionable evidence for optimizing clinical block regimens. This single-center, prospective, randomized, double-blind, controlled trial will enroll 129 patients, who will be randomly assigned in a 1:1:1 ratio to receive STB with 5 mL, 10 mL, or 15 mL of 0.4% ropivacaine. The primary outcome is the incidence of HDP at 30 min post-block. Secondary outcomes include changes in diaphragmatic excursion, peripheral oxygen saturation (SpO 2 ), sensory and motor block characteristics (onset time, duration, and extent of sensory-motor dissociation), static and dynamic visual analog scale (VAS) scores within the first 24 postoperative hours, intraoperative propofol and remifentanil consumption, and frequency of postoperative rescue analgesia requirements. All blocks will be performed by uniformly trained designated anesthesiologists using a standardized ultrasound-guided technique (high-frequency linear transducer + in-plane needle approach) to minimize technical variability. This protocol is designed to provide high-quality evidence to guide clinical decisions on LA volume selection for STB. By systematically evaluating the trade-off between analgesic efficacy and phrenic nerve involvement across three distinct LA volumes, this study addresses a key clinical dilemma in regional anesthesia for arthroscopic shoulder surgery. We hypothesize that our findings will establish a volume-dependent risk–benefit profile for STB, enabling individualized LA volume selection in clinical practice. Chinese Clinical Trial Registry, ChiCTR2400088722. Registered on 2024–08-26. www.chictr.org.cn .