The incidence and aetiology of phrenic nerve blockade associated with supraclavicular brachial plexus block.

A trial to ascertain the true incidence of inadvertent phrenic nerve block with brachial plexus block via the supraclavicular approach was carried out. Phrenic nerve block was monitored by x-ray screening of the diaphragm. There was an incidence of phrenic nerve block of 67% (10 cases of diaphragmatic paralysis in 15 brachial blocks). The possible causes of phrenic nerve block with brachial block are discussed. It is concluded that the phrenic nerve is blocked peripherally in front of the scalenus anterior.