Interscalene Block Phrenic Palsy Incidence — FRCA Final MCQ

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ModerateRegional AnaesthesiaInterscalene Block Phrenic Palsy IncidenceFRCA Final

A 42-year-old man (ASA II) is scheduled for arthroscopic rotator cuff repair. An interscalene block is planned. According to current evidence, what is the incidence of ipsilateral phrenic nerve palsy with an ultrasound-guided interscalene block?

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Correct answer: E — 30-50%

Phrenic nerve palsy (diaphragmatic paresis) occurs in nearly 100% of interscalene blocks when traditional volumes (20+ mL) are used, regardless of guidance technique. With low-volume ultrasound-guided techniques (5 mL or less), the incidence can be reduced to approximately 30-50%, but it cannot be eliminated entirely because the phrenic nerve (C3-C5) runs on the anterior surface of the anterior scalene muscle in close proximity to the C5/C6 roots targeted by the interscalene block. This is particularly important in patients with contralateral phrenic nerve dysfunction or significant respiratory disease.

Reference: El-Boghdadly K – 2017 – Phrenic nerve palsy and interscalene block; RCOA – 2023 – Regional anaesthesia