- Indications: forearm and hand surgery
- Transducer position: short axis to arm, just distal to pectoralis major insertion
- Goal: local anesthetic spread around axillary artery
- Local anesthetic: 20-25 mL
Transducer position and needle insertion in ultrasound-guided axillary brachial plexus block.
The axillary brachial plexus block offers several advantages over the other approaches to the brachial plexus. The technique is relatively simple to perform, and may be associated with a relatively lower risk of complications as compared with interscalene (e.g., spinal cord or vertebral artery puncture) or supraclavicular brachial plexus block (e.g., pneumothorax). In clinical scenarios in which access to the upper parts of the brachial plexus is difficult or impossible (e.g, local infection, burns, indwelling venous catheters), the ability to anesthetize the plexus at a more distal level may be important. The axillary brachial plexus block is also relatively simple to perform with ultrasound because of its superficial location. Although individual nerves can usually be identified in the vicinity of the axillary artery, this is not 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), and the pulsating axillary artery can be identified usually within a centimeter of the skin surface on the anteromedial aspect of the proximal arm, Figure 32-2. The artery can be associated with one or more axillary veins, often located medially to the artery. Importantly, an undue pressure with the transducer during imaging may obliterate the veins, rendering veins invisible and prone to puncture with the needle if care is not taken to avoid it. Surrounding the axillary artery are three of the four principal branches of the brachial plexus: 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 (Figure 32-2). These are seen as round hyperechoic structures, and although the previously mentioned locations relative to the artery are frequently encountered, there is considerable anatomic variation from individual to individual,. Three muscles surround the neurovascular bundle: the biceps brachii (lateral and superficial), the wedge-shaped coracobrachialis (lateral and deep), and the triceps brachii (medial and posterior). The fourth principal nerve of the brachial plexus, the musculocutaneous nerve, is found in the fascial layers between biceps and coracobrachialis muscles, though its location is variable and can be seen within either muscle. It is usually seen as a hypoechoic flattened oval with a bright hyperechoic rim. Moving the transducer proximally and distally along the long axis of the arm, the musculocutaneous nerve will appear to move toward or away from the neurovascular bundle in the fascial plane between the two muscles. Refer to Chapter 1, Essential Regional Anesthesia Anatomy for additional information on the anatomy of the axillary brachial plexus and its branches.