Anatomical pitfall of subclavian venepuncture.

Dissection of 30 human cadavers demonstrated a 45% incidence of accessory phrenic nerves crossing in front of the subclavian vein. There was a small incidence of other anomalies, including instances of the phrenic nerve crossing anterior to the subclavian vein and of the accessory phrenic nerve passing through the subclavian vein and dividing in into two separate channels. These may be hazards in the procedure of subclavian venepuncture.