Protocol: Comparative efficacy of 2 mL vs. 5 mL 0.375% ropivacaine in subparaneural upper trunk brachial plexus block for postoperative analgesia after arthroscopic shoulder surgery-a randomized noninferiority trial.

Introduction: Interscalene brachial plexus block (ISB) is the first-line analgesic technique for arthroscopic shoulder surgery, but it is associated with a > 90% incidence of ipsilateral hemidiaphragmatic paresis (HDP), which severely limits its application in patients with preexisting pulmonary dysfunction. All currently available modified nerve block techniques have failed to achieve a 0% incidence of HDP while maintaining satisfactory analgesic efficacy. Our preliminary study demonstrated that subparaneural injection of 2 mL 0.375% ropivacaine at the bifurcation of the brachial plexus upper trunk provided excellent postoperative analgesia with no observed cases of HDP. Methods and analysis: This is a prospective, single-center, randomized, non-inferiority trial conducted at Ningbo No.6 Hospital, China. A total of 100 patients undergoing elective arthroscopic shoulder surgery will be randomized in a 1:1 ratio to receive either 2 mL or 5 mL of 0.375% ropivacaine via ultrasound-guided subparaneural injection at the upper trunk bifurcation. The dual co-primary endpoints are the pre-rescue Numerical Rating Scale (NRS) pain score immediately after full consciousness in the post-anesthesia care unit (PACU) (non-inferiority margin = 1 point) and the incidence of ipsilateral HDP assessed before PACU discharge. Secondary outcomes include diaphragmatic function parameters, pulmonary function, perioperative analgesic consumption, recovery indicators, and adverse events. All statistical analyses will be performed according to the pre-specified statistical analysis plan, with the intention-to-treat population as the primary analysis set. Clinical trial registration: http://www.chictr.org.cn, ChiCTR2500114139.