The diagnosis of phrenic nerve block on chest X-ray by a double-exposure technique

Diaphragmatic paralysis due to phrenic nerve block is a frequent complication of brachial plexus blocks performed above the clavicle. Farrar et al. reported incidences of 36, 36, and 38%, respectively, when routine chest x-rays were taken 4 h following interscalene, subclavian perivascular, and Kulenkampff supraclavicular techniques of brachial plexus blocks. Knoblanche demonstrated a higher incidence of 67% when fluoroscopic exmainations were performed to evaluate diaphragmatic movement in 15 patients within 3 h following subclavian perivascular brachial plexus blocks. Reports of the diagnosis of phrenic nerve block have previously relied upon clinical symptomatology, plain chest x-ray, or fluoroscopy. Recently, we have used a double-exposure technique that has allowed us to easily detect the presence or absence of phrenic nerve block on a single chest x-ray.