Figure 28-1. Anatomy of the brachial plexus at axilla and at the midhumeral level.

Figure 28-2. Landmarks for the classical approach to axillary brachial plexus block.

EQUIPMENT

• Sterile towels and 4-in. x 4-in. gauze packs

• Sterile gloves, marking pen, and a skin electrode

• 1-in., 25-gauge needle for skin infiltration

• 1- to 1.5-in. atraumatic, insulated stimulating needle

• 20-mL syringes containing LA of choice

• Peripheral nerve stimulator

INJECTION TECHNIQUES

Arm Position for the Block

The arm to be operated on is abducted approximately 90 degrees (see Figure 28-2). The elbow is flexed and the forearm rests comfortably, supported by a pillow. A skin electrode is typically placed on the patient’s shoulder and connected to the positive electrode (anode) of the nerve stimulator. After scrubbing the axilla, the arterial pulse is palpated at the level of the major pectoral muscle, and the subcutaneous tissue overlying the artery is infiltrated with 4 to 5 mL of LA (to block the intercostobrachial and medial cutaneous nerves of the arm). Numerous techniques and approaches to the brachial plexus block at the level about the axilla have been described. Discussion of all the technique variations is beyond the scope of this text; we will describe some of the best studied and clinically useful techniques.

Clinical Pearl

Various approaches and techniques described in the following sections all have their advantages and disadvantages. However, a triple-injection axillary block is probably the fastest and most efficient technique for axillary brachial plexus blockade.

NERVE STIMULATION TECHNIQUES

Single-Injection (Stimulation) Technique

1. The nerve stimulator is set to deliver 0.5–1.0 mA (2 Hz, 0.1 msec); electrical connections with the needle and the neutral electrode are checked.

2. Depending on the surgical site (palmar and medial or dorsal and lateral aspects of the hand/forearm), the stimulating needle is inserted above the arterial pulse (toward the median nerve) or below the arterial pulse (toward the radial nerve), respectively (Figures 28–3 and 28–4).

3. As the brachial superficial fascia is penetrated, a characteristic “click” is often felt, and the current amplitude is slowly increased (eg, at 1-mA increments) until the desired twitch (flexion or extension of the wrist and fingers) is obtained. This helps avoid painful electrical paresthesia when the elastic fascia suddenly “gives in” and the needle enters the neurovascular sheath.²⁷

4. After the initial motor response is obtained, the needle is slowly advanced toward the stimulated nerve while reducing the amplitude.

5. Once the stimulation is obtained using a current intensity of 0.3 to 0.5 mA, the entire volume of LA is injected slowly, while intermittently aspirating to reduce the risk of accidental intravascular injection. This results in substantial spread of the LA within the tissue layers encompassing the brachial plexus (Figure 28-5).

Figure 28-3. Median nerve block: The needle is inserted above the pulse ofthe axillary (brachial) artery. CB = coracobrachialis muscle.

Figure 28-4. Radial nerve block: The needle is inserted below the pulse of the axillary (brachial) artery. CB = coracobrachialis muscle.

Clinical Pearls

Arterial pulse palpation may prove challenging in some patients. In these patients, the first obtained motor response can be used to guide needle redirection to achieve the desired response.

Elbow flexion (stimulation of the coracobrachialis muscle or the musculocutaneous nerve) indicates that the needle is outside the neurovascular sheath; the needle should be redirected downward and more superficially.

Extension of the wrist and hand (radial nerve) indicates that the needle is below the artery.

The more difficult differentiation is between the median and the ulnar nerves, which both result in wrist/finger flexion. In this scenario, the following method can be used to differentiate between the two nerves:

When flexion is accompanied by forearm pronation, the stimulated nerve is the median (the needle is positioned above the artery).

Another way to differentiate between these two nerves is by palpation of the flexor tendons at the wrist. Median nerve stimulation produces movements of the palmaris longus and the flexor carpi radialis tendons, which lie in the middle of the wrist, whereas ulnar nerve stimulation produces movement of the flexor carpi ulnaris tendon, which lies medially.

Decreasing the intensity of the output current of the nerve stimulator helps facilitate differentiation between median and ulnar nerve stimulation.

Figure 28-5. Distribution of local anesthetic injected during axillary brachial plexus blockade. NR = nervus radialis.

Double-Injection Technique

1. The stimulating needle is first inserted above the artery, below the coracobrachialis muscle (see Figure 28-3). After penetrating the fascia, the amplitude is increased until synchronous wrist flexion/pronation and flexion of the first three fingers are obtained (median nerve stimulation). The needle is advanced slowly toward this nerve while reducing the amplitude to 0.3 to 0.5 mA. At this point, half of the planned volume of LA is slowly injected with intermittent aspiration to rule out intravascular injection.

2. The needle is then withdrawn and inserted below the artery and above the triceps muscle (see Figure 28-4). The fascia is again penetrated and the amplitude slowly increased. The first response is usually either arm extension (muscular branches to the triceps) or thumb adduction and flexion of the last two fingers (ulnar nerve). However, these responses are ignored, and the needle is advanced deeper, often slightly upward, behind the artery (Figure 28-6) until wrist and finger extension is obtained (radial nerve). After stimulation is obtained using a current intensity lower than 0.5 mA, the remaining volume of LA is slowly injected with intermittent aspiration.

Multiple-Injection Technique

Needle insertion sites are identical to those for the doubleinjection technique

1. After electrolocation of the median nerve, 5–10 mL of the LA volume is injected (see Figure 28-3).

2. The needle is withdrawn subcutaneously and redirected obliquely, above and into the coracobrachialis muscle. After obtaining stimulation-synchronous elbow flexion, the amplitude is reduced to 0.3 to 0.5 mA and another 5–10 mL of LA is injected.

3. The needle is removed and inserted below the artery (see Figure 28-4). The’first stimulated nerve is usually the ulnar, into which 5–10 mL of LA is injected.

4. The needle is advanced deeper until the radial nerve is found (see under Double-Injection Technique.)

Clinical Pearls

Two recent studies by Sia and colleagues^23,28 suggest that two separate injections below the artery do not improve success rates, and therefore only one such injection is needed. This injection is made close to the radial nerve and should contain half of the planned LA volume.

Electrolocation of multiple nerves may occasionally take some time. Because the first injection of the LA injection in the vicinity of the median nerve may partially block the ulnar nerve, the search for the nerves should be made expeditiously to minimize the risk of nerve injury by advancing needle or intraneural injection into an anesthetized nerve.

For these reasons, this technique could be considered an advanced regional anesthesia technique. Careful assessment of resistance to injection by an experienced practitioner or objective monitoring of injection pressure should be used with each injection.

Transarterial Technique

The transarterial technique is perhaps most commonly used for axillary blockade. This relatively simple technique does not rely on a nerve stimulator; instead, placement of the needle within the neurovascular sheath is ensured by relying on the pulse of the axillary artery:

• The axillary artery is palpated and stabilized using a two- finger palpation technique.

• As the needle is advanced toward the pulse of the axillary artery, bright red arterial blood is aspirated. A thin, long-beveled needle (typically 1.5-in., 25-gauge) is used to minimize the risk of axillary hematoma.

• The needle is advanced deeper until blood cannot be aspirated (the tip of the needle has exited the artery) and half of the volume of the LA is injected behind the posterior wall. This should block the radial nerve.

• The needle is slowly withdrawn while aspirating. As the needle enters the axillary artery, bright red blood is again aspirated.

• The withdrawal of the needle is continued until blood can not be aspirated (the needle exits the artery and its tip is positioned superficial [medial] to the artery inside the neurovascular sheath).

• The remaining volume of LA is injected superficial to the anterior wall to block the median and the ulnar nerves.

Figure 28-6. Spatial arrangement of the terminal nerves of the brachial plexus in the axilla. M = median nerve, A = artery, V = vein, R = radial nerve, U = ulnar nerve.

Clinical Pearls

A transarterial injection is made as high up in the axilla as possible, and the needle should traverse the artery at an oblique angle. This reduces the risk of making the injection behind the artery intramuscularly and improves the spread of the LA to the plexus cords to block the musculocutaneous nerve.