Upper limb peripheral nerve blocks

The upper limb is supplied by nerves of the brachial plexus. The brachial plexus is formed by the anterior primary rami of the lower four cervical nerves (C5–C8) and the first thoracic nerve (T1).^6,7 In some individuals there may also be contributions from the C4 and T2 nerve roots. The plexus supplies motor innervation to all the muscles of the upper limb with the exception of the trapezius and levator scapula muscles. It supplies cutaneous innervation to the upper limb with the exception of the area of the axilla (upper inner arm), which is supplied by the intercostobrachial nerve. Above the shoulder is supplied by the supraclavicular nerve (cervical plexus), and the dorsal scapular area is supplied by cutaneous branches of spinal nerves. The plexus has five terminal branches (median, ulnar, radial, musculocutaneous and axillary nerves) in addition to a number of smaller branches. The innervations of the major joints of the upper limb are highlighted in Table 9.1. A more detailed description of upper limb anatomy can be found in Chapter 14. It is possible to block the brachial plexus at various levels as it leaves the intervertebral foramina and traverses towards the periphery. The most proximal approach at the level of the nerve roots is the interscalene approach; the supraclavicular block is performed at the level of the trunks, while the infraclavicular block is performed at the level of the cords, with axillary approach at the level of the terminal branches. All of these blocks can be successfully performed with either nerve stimulation or with ultrasound guided techniques (Ch. 7).^2–4

Table 9.1 Innervations of the major joints of the upper limb

The interscalene approach is suitable for surgeries of the shoulder and upper arm, and can be performed with the arm in almost any position. It blocks the plexus close to the nerve roots at about the level of the cricoids cartilage (C6).⁶ This may help explain why there is less spread to the lower roots, resulting in poor block of the ulnar nerve (C8, T1). The posterior shoulder will not be anesthetized, requiring wound infiltration for the port site for shoulder arthroscopies. Equally, the anterior port for arthroscopy may also be missed because the skin is supplied by T2. A supplemental skin infiltration needs to be made over the distribution of T2 to ensure the anterior port or the lower end of a total shoulder incision is adequately anesthetized. The phrenic nerve is paralyzed with this approach as it lies on the anterior scalene muscle, so caution should be exercised in patients with severe respiratory co-morbidities. In addition, patients may develop hoarseness and ptosis. This is a superficial block and complications are rare. However, serious complications have been reported with this block, including spinal cord injury, vascular injection and pneumothorax.⁸

The supraclavicular approach is suitable for surgeries of the upper arm, elbow and hand, and is performed at the level of the trunks of the brachial plexus. It is frequently referred to as the spinal anesthetic of the upper limb as it can provide complete anesthesia of the limb below the shoulder in a consistent time-efficient manner. In the past, some anesthetists were cautious about performing this block because of the rare complication of pneumothorax, and the fact that the landmarks were not easy to ascertain, particularly in obese patients. However, the advent of ultrasound has resulted in a huge increase in the utilization of this block, where the plexus can be seen lying posterior and lateral to the subclavian artery on the first rib (Fig. 9.1). Local anesthetic can be preferentially injected around the lower trunk (C8, T1) of the plexus, particularly when used for hand surgery. Use of this block may still result in phrenic nerve paralysis (50%) and Horner’s syndrome.⁶ Placement of a continuous catheter at this site (supraclavicular fossa) for post operative analgesia is easy to secure and less likely to become dislodged (Fig. 9.2).

Figure 9.1 Ultrasound-guided supraclavicular block. (A) The nerve plexus (arrows) is seen lying lateral to the subclavian artery (Art). (B) The tip and shaft of the needle is seen lateral to the artery after injection of local anesthetic.

Figure 9.2 Supraclavicular continuous catheter. Placed for intra-operative anesthesia and postoperative analgesia in a patient with severe hand trauma (4-finger amputation).

The infraclavicular approach to the brachial plexus is ideal for surgeries from the elbow to the hand. The block is performed at the level of the cords of the brachial plexus, as they lie in close proximity to the subclavian (axillary) artery deep to the pectoralis major muscle. The block can be performed with the arm in any position, whereas with the axillary approach the arm is abducted. Blocking the plexus at this level typically results in satisfactory anesthesia of the musculocutaneous nerve. Because the nerves lie deep to the muscle, this block is particularly suited to a continuous catheter technique where the catheter can be secured to the anterior chest wall.

The axillary approach to the brachial plexus anesthetizes the terminal branches of the plexus, as they lie in close proximity to the axillary artery.⁶ It is ideal for surgeries below the elbow, particularly hand surgery. This block is safe and easy to perform and is therefore widely used. The anesthetist needs to be aware that there are multiple vessels (arteries and veins) in close proximity to the nerves and care should be taken to avoid intravascular injection. A single injection technique is associated with a significant failure, therefore a multiple injection technique should be used or the block performed under ultrasound guidance to ensure adequate spread of local anesthetic⁹ (Fig. 9.3). The musculocutaneous nerve lies between the biceps and coracobrachialis muscle and may be some distance away from the other branches of the plexus which lie close to the artery. It is critical to block the musculocutaneous nerve, as it supplies the flexor muscles of the arm and the skin over the lateral surface of the forearm.

Figure 9.3 Ultrasound-guided axillary block. The plaster cast is left in situ, as there is no need to utilize nerve stimulation.

The utilization of elbow and forearm blocks is discussed in Chapters 21 and 22. These blocks are easy to perform, particularly when ultrasound guidance is used (Fig. 9.4). These techniques are useful both as the primary anesthetic, and also for postoperative analgesia. Consideration should be given as to whether the surgeon is using a tourniquet and in what location. Upper arm tourniquets can be used for short periods of time, but longer use will require anesthesia of the tourniquet location. In such cases, a distal forearm or elbow block performed with a long acting local anesthetic (to provide postoperative analgesia) can be used in combination with a more proximal block such as infraclavicular or axillary block, using a shorter-acting local anesthetic (lignocaine). The more distal block should be performed first to minimize the risk of unrecognized intraneural injection. These blocks are also frequently used as ‘rescue’ blocks, where following a more proximal block there is incomplete anesthesia in a branch of the plexus. This branch can then be blocked at the elbow or forearm. Again, caution should be exercised, as rescue blocks may be associated with a higher incidence of nerve injury.

Figure 9.4 An ultrasound scan of the radial nerve (arrow) at the elbow, lying above the bone, between the brachioradialis (BR) and the brachialis muscles (B).

The intercostobrachial nerve (T2) supplies the area of the axilla (upper inner arm) which is important for certain upper arm procedures. In addition, this is where an upper arm tourniquet is typically located. While tourniquet pain is largely related to muscle ischemia, anesthetizing the skin in this area will improve patient comfort. This is easily achieved using subcutaneous infiltration of local anesthetic around the medial aspect of the upper arm (Fig. 9.5). The supraclavicular nerve block (cervical plexus) can be performed by injecting local anesthetic along the posterior border of the sternocleidomastoid muscle (Ch. 11).

Figure 9.5 The intercostobrachial nerve (T2) is blocked using subcutaneous infiltration of local anesthetic around the medial aspect of the upper arm (along the red line).