Effect of an Optimized Ultrasound-Guided Costoclavicular Brachial Plexus Block Strategy on Anesthetic Efficacy and Diaphragmatic Function in Elderly Patients Undergoing Internal Fixation of Proximal Humeral Fractures: A Multicenter, Prospective, Randomized Controlled Clinical Trial

Background: Proximal humeral fractures are common in elderly patients and often require surgical fixation (open reduction and internal fixation). Traditional regional anesthesia techniques, such as the interscalene brachial plexus block, may provide incomplete pain relief in the medial upper arm area and carry a high risk of hemidiaphragmatic paralysis, which can lead to breathing difficulties.

Objective: This study aims to evaluate whether an optimized nerve block strategy-ultrasound-guided costoclavicular brachial plexus block combined with superficial cervical plexus block and T2 thoracic paravertebral block-improves anesthetic success and reduces diaphragm dysfunction compared to the traditional interscalene approach in elderly patients undergoing proximal humeral fracture surgery.

Study Design: This is a multicenter, prospective, randomized, controlled, double-blind (participants and outcome assessors), superiority clinical trial.

Population: A total of 356 elderly patients (aged ≥65 years) with unilateral proximal humeral fractures scheduled for open reduction and internal fixation via an anterior surgical approach will be enrolled from three centers in Shanghai, China.

Intervention: Participants will be randomly assigned in a 1:1 ratio to one of two groups:

• Experimental Group (Optimized Strategy): Receives ultrasound-guided costoclavicular brachial plexus block + superficial cervical plexus block + T2 thoracic paravertebral block (0.375% ropivacaine 20 mL for brachial plexus, 0.25% ropivacaine 10 mL for each of the other blocks).
• Control Group (Traditional Strategy): Receives ultrasound-guided interscalene brachial plexus block + superficial cervical plexus block + T2 thoracic paravertebral block (same drug regimen).

All nerve blocks will be performed under ultrasound guidance by a single anesthesiologist. Patients and outcome assessors will be blinded to group assignment; the performing anesthesiologist cannot be blinded due to the distinct anatomical approaches.

Main Outcomes:

• Primary Outcome: Nerve block success rate, defined as no pain or only mild pain requiring no rescue analgesics (e.g., intravenous opioids, conversion to general anesthesia, or local infiltration) during surgery.
• Key Secondary Outcomes: Rate of hemidiaphragmatic paralysis (assessed by ultrasound M-mode); rate of conversion to general anesthesia; postoperative pain (NRS, 0-10) at 24 hours; perioperative stress biomarkers (cortisol, ACTH, IL-6, HMGB-1, CRP, galectin-3); and postoperative shoulder function recovery.

Safety Monitoring: Adverse events, including unplanned conversion to general anesthesia, respiratory depression, pneumothorax, and severe hemidiaphragmatic paralysis, will be recorded and managed according to predefined protocols. An independent Data Monitoring Committee will review safety data and conduct interim analyses for futility.

Study Duration: The study is expected to take approximately 24 months from first patient enrollment to final follow-up completion.

Ethical Approval: This study has been approved by the Ethics Committee of Shanghai Tongren Hospital. Approvals from the ethics committees of the other participating centers (Shanghai Sixth People's Hospital and Shanghai Xuhui Central Hospital) will be obtained before study initiation at those sites.