brachial plexus anesthesia, an anesthetic block of the upper extremity, performed by injecting local anesthetic near the plexus formed by the last four cervical and first two thoracic spinal nerves. The plexus extends from the transverse processes of the spine to the apex of the axilla, where the terminal nerves are formed. Because of the anatomy of this area, many approaches are possible. Approaches include the axillary (in the armpit), supraclavicular and infraclavicular (above and below the collarbone), and interscalene (between the anterior and middle scalene muscles of the neck). Various approaches may result in Horner’s syndrome, phrenic nerve block, pneumothorax, recurrent laryngeal paralysis, persistent sensory deficits, venous or arterial puncture, subarachnoid injection, paresthesias, or hematoma. Also called brachial plexus block. See also regional anesthesia.
