An interscalene brachial plexus block is performed under ultrasound guidance. Which of the following complications is unique to this approach due to the proximity of specific anatomical structures?

• A Radial nerve palsy
• B Anterior interosseous nerve injury
• C Medial cutaneous nerve of forearm injury
• D Ipsilateral phrenic nerve palsy causing 25% reduction in pulmonary function ✓

Explanation

Interscalene block targets the brachial plexus at C5–C7 level (trunks/roots) and virtually always blocks the ipsilateral phrenic nerve (C3–C5 origin, running anterior to the anterior scalene muscle). This causes ipsilateral hemidiaphragm paralysis and approximately 25% reduction in spirometric values. This is usually well-tolerated in patients with normal lung function but is an important consideration (and relative contraindication) in patients with contralateral phrenic palsy, severe COPD, or when the contralateral lung is absent. Horner syndrome (ptosis, miosis, anhidrosis) and recurrent laryngeal nerve block are additional complications.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.