Background and indications: Traditionally, axillary block was the most commonly performed of the brachial plexus blocks because of the ease of locating the plexus relative to the axillary artery by palpation. It does have some drawbacks. The arm must be abducted and the elbow flexed to access the axilla. This can be painful for patients with fractures and impossible for people with contractures or arthritis. In addition, it was often difficult to anesthetize the musculocuTaneous nerve with a blind or stimulation technique. The addition of ultrasound allows the user to identify all four nerves (median, radial, ulnar, musculocuTaneous) necessary for a successful block. That, coupled with the safety of the block, make it an attractive procedure when ultrasound is used. The block is used for surgery of the elbow, forearm, and hand. A separate block of the intercostal brachial nerve is required when the incision is along the medial aspect of the extremity.

Anatomy: The biceps muscle lies anterosuperior to the neurovascular bundle, the coracobrachialis muscle is superior to the neurovascular bundle, and the triceps muscle is inferior to the neurovascular bundle. The humerus lies deep to the neurovascular bundle. The brachial artery and one to two brachial veins are evident in the neurovascular bundle. The radial, median, and ulnar nerves are found within the neurovascular bundle (Figs. 20.1 and 20.2). Most commonly, the median nerve is anterior or cephaloanterior to the artery. The radial nerve is most commonly posterior or posteroinferior to the artery, the ulnar nerve is most commonly found inferior or anteroinferior to the artery. Proximal in the axilla, the musculocuTaneous nerve may be found cephaloposterior to the artery. In more distal sites in the axilla, the musculocuTaneous nerve is usually found in the fascia between the biceps and coracobrachialis muscles 1 to 2 cm cephaloposterior to the artery. CuTaneous nerves of the arm or forearm may also be visualized (Figs. 20.1 and 20.2).

Patient position: Supine, with ipsilateral arm abducted, externally rotated, and flexed at the elbow.

Transducer: 25- or 38-mm linear transducer oscillating at 13 MHz.