The costoclavicular approach of the infraclavicular brachial plexus block is widely used for upper extremity surgeries due to its reliable anatomy and high success rates. Patient positioning, particularly the degree of arm abduction, may influence the spread of local anesthetic and the characteristics of the block. However, the optimal arm abduction angle during this procedure remains unclear.

This prospective randomized controlled trial aims to investigate the effect of two different arm abduction angles (90° and 120°) on block onset time and block success in patients undergoing hand, wrist, and forearm surgery under ultrasound-guided costoclavicular brachial plexus block.

Patients will be randomly assigned to one of two groups according to the degree of arm abduction. The primary outcome is block onset time. Secondary outcomes include block success, sensory and motor block characteristics, perfusion index changes, hemodynamic parameters, readiness for surgery at 15 and 20 minutes, block performance time, need for additional anesthesia, postoperative neurological evaluation at 4 and 24 hours, complications, and patient satisfaction.

The findings of this study are expected to provide evidence on optimal patient positioning to improve the effectiveness and reliability of ultrasound-guided costoclavicular brachial plexus block.

The costoclavicular approach is a recently described infraclavicular technique for brachial plexus block that provides reliable anesthesia for upper extremity surgeries. Due to the compact arrangement of the cords in the costoclavicular space, this technique has gained popularity for its high success rates and consistent anatomy. However, procedural factors such as patient positioning may influence the distribution of local anesthetic and the effectiveness of the block.

Arm abduction is known to alter the anatomical relationships within the infraclavicular region, potentially affecting needle visualization, spread of local anesthetic, and block characteristics. Despite its clinical relevance, there is limited evidence regarding the optimal degree of arm abduction during ultrasound-guided costoclavicular brachial plexus block.

This prospective randomized controlled study aims to compare two different arm abduction angles 90° and 120° in patients undergoing elective hand, wrist, and forearm surgery. After obtaining written informed consent, eligible patients will be randomly assigned into two groups according to the degree of arm abduction.

All procedures will be performed under ultrasound guidance using a standardized technique. The local anesthetic will be administered in the costoclavicular space, and block characteristics will be assessed systematically. The primary outcome is block onset time, defined as the time from completion of local anesthetic injection to the achievement of adequate sensory block for surgery.

Secondary outcomes include block success, sensory and motor block scores, perfusion index measurements, hemodynamic parameters, readiness for surgery at 15 and 20 minutes, block performance time, need for additional anesthesia or conversion to general anesthesia, early complications, postoperative neurological evaluation at 4 and 24 hours, and patient satisfaction assessed using a Likert scale.

The results of this study are expected to provide valuable evidence regarding optimal patient positioning and contribute to improving the clinical effectiveness and reliability of ultrasound-guided costoclavicular brachial plexus block.

Inclusion Criteria:

• Patients aged between 18 and 80 years.
• Patients scheduled for elective upper extremity surgery (hand, wrist, forearm).
• Patients classified as ASA I-III.
• Patients who provide informed consent after being informed about the study.

Exclusion Criteria:

• History of previous surgery, scar tissue, tumor, or trauma that may alter brachial plexus anatomy.
• Presence of infection, hematoma, severe edema, burn, or open wound at the block application site.
• Known allergy to local anesthetics or other medications used in the study.
• Coagulopathy, use of anticoagulants, or platelet count < 100,000/mm³.
• History of peripheral neuropathy, neurological deficit, cervical radiculopathy, or CRPS.
• Pregnancy or breastfeeding.
• Patients with BMI < 18 kg/m².
• Patients with BMI > 35 kg/m².
• Severe cardiac, pulmonary, renal, or hepatic failure.
• Mental retardation, communication difficulties, or lack of cooperation.
• Deformity, amputation, or large mass in the surgical extremity that may interfere with sensorimotor assessment.
• Preoperative significant sensory loss, motor weakness, or signs of neurological disease.
• Severe anemia (Hb < 9 g/dL) or polycythemia (Hb > 18 g/dL).
• Psychiatric disorders, substance abuse, or any condition that may interfere with study compliance.

This study is an open-label trial. Due to the nature of the intervention (different arm positions), blinding is not feasible