An Ultrasound Study of the Phrenic Nerve in the Posterior Cervical Triangle: Implications for the Interscalene Brachial Plexus Block

This descriptive study found that the phrenic nerve and brachial plexus are within 2 mm of each other at the cricoid cartilage level, with additional 3 mm separation for every cm more caudal in the neck. Clinical trials with imaging guidance are needed to establish whether brachial plexus selective blocks can be consistently achieved above the clavicle.