This randomized controlled trial aims to compare the incidence of hemidiaphragmatic paralysis (HDP) following ultrasound-guided interscalene block (ISB) versus shoulder pericapsular nerve group (PENG) block in patients undergoing elective shoulder surgery under general anesthesia.

The primary objective is to determine whether the shoulder PENG block reduces the incidence of HDP compared with conventional intrafascial ISB. HDP will be assessed using ultrasound measurement of diaphragmatic excursion 30 minutes after block performance

Interscalene block is widely used for shoulder surgery but is frequently associated with ipsilateral hemidiaphragmatic paralysis due to phrenic nerve involvement. The shoulder PENG block is a more distal pericapsular technique targeting articular branches and may reduce diaphragmatic impairment.

This prospective, parallel-group, randomized controlled trial will enroll 68 adult patients scheduled for elective shoulder surgery. Participants will be randomly assigned (1:1) to receive either ultrasound-guided intrafascial interscalene block or ultrasound-guided shoulder PENG block.

Both groups will receive 15 mL of 0.25% bupivacaine (total dose 37.5 mg). Diaphragmatic excursion will be measured at baseline and 30 minutes after block performance using M-mode ultrasonography by a blinded assessor.

The primary endpoint is hemidiaphragmatic paralysis defined as ≥25% reduction in diaphragmatic excursion from baseline. Partial and complete paralysis will be analyzed as a composite binary outcome.

Inclusion Criteria:

• ASA physical status I-III
• Scheduled for elective shoulder surgery under general anesthesia
• Able to provide informed consent

Exclusion Criteria:

• Pre-existing diaphragmatic dysfunction
• Severe COPD or restrictive pulmonary disease
• Neuromuscular disorders
• BMI > 40 kg/m²
• Coagulopathy
• Infection at injection site
• Allergy to local anesthetics
• Inability to undergo diaphragmatic ultrasound assessment