AXILLARY BRACHIAL PLEXUS BLOCK AT A GLANCE
Indications: elbow, forearm and hand surgery (Figure 32E–1)
Transducer position: short axis to arm, just distal to the pectoralis major insertion
Goal: local anesthetic spread around axillary artery
Local anesthetic: 15–20 mL
Sensory distribution after axillary brachial plexus block.
The axillary brachial plexus block is relatively simple to perform and may be associated with a lower risk of complications compared with interscalene (eg, spinal cord or vertebral artery puncture) and supraclavicular brachial plexus blocks (eg, pneumothorax). In clinical scenarios in which access to the upper parts of the brachial plexus is difficult or impossible (eg, local infection, burns, indwelling venous catheters), the ability to anesthetize the plexus at a more distal level may be important. Although individual nerves can usually be identified this is not absolutely necessary because the deposition of local anesthetic around the axillary artery is sufficient for an effective block.
The structures of interest are superficial (1–3 cm below the skin), and the axillary artery is readily identified within a centimeter of the skin surface on the medial aspect of the proximal arm (Figure 32E–2). The artery is accompanied by one or more axillary veins, often located medially to the artery. Importantly, excessive pressure with the transducer during imaging may compress the veins, rendering veins invisible and prone to puncture with the needle. Surrounding the axillary artery, three of the four principal branches of the brachial plexus can be seen: the median (superficial and lateral to the artery), the ulnar (superficial and medial to the artery), and the radial (posterior and lateral or medial to the artery) nerves (see Figure 32E–2). The nerves appear as round hyperechoic structures. Several authors have reported the anatomical variations of the nerves relative to the axillary artery;1,2,3,4 Figure 32E–3 illustrates the most common patterns.
(A) Cross-sectional anatomy of the axillary fossa and ultrasound image (B) of the terminal nerves of brachial plexus. The BP is seen scattered around the axillary artery and enclosed within the adipose tissue compartment containing the axillary artery (AA), and axillary veins (AV). MCN, musculocutaneous nerve. MN, median nerve; RN, radial nerve; UN, ulnar nerve; MACN, median antebrachial cutaneous nerve; CBM, corachobrachialis muscle.
Most common patterns of nerve location around the axillary artery in ultrasound-guided axillary brachial plexus block.4
Three muscles surround the neurovascular bundle: the biceps (anterior and superficial), the wedge-shaped coracobrachialis (anterior and deep), ...