Hemidiaphragmatic paresis after ultrasound-guided shoulder blocks: systematic review and meta-analysis of phrenic-sparing techniques

This systematic review and meta-analysis evaluates the incidence and comparative risk of hemidiaphragmatic paresis (HDP) associated with ultrasound-guided regional anesthesia techniques for shoulder surgery. The review focuses on technical modifications and alternative regional anesthesia approaches intended to reduce phrenic nerve involvement, including low-volume interscalene and superior trunk blocks, extrafascial interscalene injection, superior trunk block, suprascapular-based blocks, costoclavicular block, infraclavicular-subomohyoid approaches, and other phrenic-sparing strategies. The primary outcome is objectively assessed HDP, principally diagnosed using diaphragmatic ultrasonography. Secondary outcomes include diaphragmatic excursion, pulmonary function, oxygenation and respiratory symptoms, postoperative pain, opioid or rescue analgesic requirements, block success, duration of analgesia, and adverse events. Eligible studies include randomized controlled trials and comparative non-randomized clinical studies involving adults undergoing shoulder surgery. Randomized studies are assessed using the Cochrane Risk of Bias 2 tool, and non-randomized comparative studies using ROBINS-I. Comparative dichotomous HDP outcomes are summarized using risk ratios with 95% confidence intervals and random-effects meta-analysis where clinically and methodologically appropriate. This OSF registration is retrospective. Study screening, data extraction, and quantitative analyses had already been initiated before submission of this registration. The purpose of the registration is to provide a transparent, time-stamped record of the review question, eligibility criteria, search strategy, outcome definitions, risk-of-bias methods, statistical analysis plan, and methodological amendments made during the review process.