- Indications: forearm and hand surgery
- Landmarks: axillary artery pulse
- Any of the following three end points: nerve stimulation, hand twitch at 0.3-0.5 mA current; hand paresthesia; arterial blood on aspiration (axillary artery)
- Local anesthetic: 20–30 mL
The needle is inserted toward the axillary artery (line) until either motor response of the hand or arterial blood on aspiration is obtained.
The axillary brachial plexus block was first described by Halsted in 1884 at the Roosevelt Hospital in New York City. The axillary brachial plexus block is one of the most commonly used regional anesthesia techniques. The proximity of the terminal nerves of the brachial plexus to the axillary artery makes identification of the landmarks consistent (axillary artery) equally for both the nerve stimulator and surface-based ultrasound-guided techniques. The axillary block is an excellent choice of anesthesia technique for elbow, forearm, and hand surgery.
By the time the brachial plexus passes behind the lower border of the pectoralis minor muscle in the axilla, the cords quickly begin to form the principal terminal nerves of the brachial plexus, namely, the median, ulnar, radial, and musculocutaneous nerves (Figure 15-2). The arrangement of the individual nerves and their relationship to the axillary artery is important in axillary blockade (Figure 15-3). With the arm abducted at 90° and the axillary arterial pulsation as a point of reference, the nerves are located as follows: The median nerve is positioned superficially and immediately above the pulse; the ulnar nerve is found superficial slightly deeper than the median nerve; the radial nerve is located behind the pulse. The musculocutaneous nerve can be found 1 to 3 cm deeper and above the pulse, often outside the brachial plexus sheath as it moves distally away from the axillary fossa (Figure 14-2).
Anatomy of the brachial plexus in the axilla.
musculocutaneous nerve as it enters the coracobrachialis muscle.
coracoid brachialis muscle. Pectoralis muscles are show retracted laterally (right upper corner).
Spatial organization of the brachial plexus in the axilla. Note that the musculocutaneous nerve is outside of the axillary plexus sheath.
The musculocutaneous nerve is a terminal branch of the lateral cord. It pierces the coracobrachialis muscle to descend between the biceps and brachialis muscles, giving innervation to both. The nerve continues distally as the lateral cutaneous nerve of the forearm, which emerges from the deep fascia between the biceps and brachioradialis to emerge superficially at the level of the cubital fossa. From here on, the nerve supplies cutaneous sensory branches to the lateral aspect of the forearm.