Distribution of anesthesia consists of the entire arm, including the hand, wrist, forearm, elbow, and most of the upper arm.

Indications are similar to those for axillary block; hand, forearm, elbow and arteriovenous fistula surgery.

Infraclavicular block provides greater coverage and obviates the need for special arm positioning (abduction).

Indications for infraclavicular block are similar to axillary blockade but expanded due to the advantages of reaching the plexus at a higher level. The approach is applicable for any surgery up to but noř including the shoulder. Complete anesthesia of the arm is obtained from the lower shoulder to the hand. There have been reports of difficulty in blocking the medial cutaneous nerve, a branch of the medial cord innervating the upper inner aspect of the arm. Rodriquez and colleagues postulated that, this could be a result of the dominance of the intercostobrachial nerve (second thoracic root) in those patients.¹⁶ Fortunately, tourniquet is well tolerated without supplementation of the intercostobrachial nerve; however if this area is involved in the surgery the medial upper arm should be specifically tested and the intercostobrachial nerve should be additionally blocked.

Not having to abduct the arm or include separate injections for the musculocutaneous or intercostobrachial nerve presents an advantage over the axillary approach. This is of significant value in patients whose injury precludes movement or for patients with arthritis or those whose shoulders cannot abduct for axillary block. Bilateral blocks can be carried out without fear of blocking the phrenic nerve. The coracoid process and clavicle landmarks are easily palpable even in obese patients. Infraclavicular access to the brachial plexus is also ideal for continuous catheter fixation and long-term infusion.

Other than an infection at or near the site or existing coagulopathy, there are no block-specific contraindications to infraclavicular block. Coagulopathy is relative and based on the risk-vs-benefit ratio. The primary concern is that should the artery be punctured, compression is difficult in this area. In patients with normal coagulation many punctures of the artery have been reported with no major problems occurring.

FUNCTIONAL ANATOMY

Clinical Pearls

Block occurs at the cord level of the brachial plexus below the clavicle.

Three cords surround the axillary artery.

The organization of the brachial plexus is complex in this area and anatomic variability exists.

Diagrams and the anatomic names of cords are often misleading; the relationship found clinically may differ.

The lateral cord is the most superficial, the posterior cord is encountered next, the medial cord is the deepest and is below the axillary artery.

The lateral cord and the medial cord both contribute fibers to the median nerve.

The posterior cord contains all of the radial nerve.

The musculocutaneous nerve is often outside but very close to the lateral cord.

The pertinent anatomy for this block begins at the level of brachial plexus divisions and extends to include transition to the cords of the brachial plexus (Figure 27-1). Divisions exist as the brachial plexus crosses the first rib into the infraclavicular area. They originate from the trunks and divide into anterior and posterior divisions, thus, the origin of the name division. Divisions are based on embryonic migration (see Chapter 2, Embryology) and locality. The anterior divisions usually supply flexor muscles (which are most often positioned anterior) and posterior divisions usually supply extensor muscles (which are generally posterior).

The brachial plexus makes most of its major changes in the infraclavicular area in just a few centimeters as it twists and turns from a parallel course in the neck to circumferentially surround the axillary artery in the infraclavicular area and progresses into the axilla as terminal nerves. Mixing of the nerves occurs, and although this is a great protective mechanism for the body its organization can be quite complex. In addition, the anatomic terms used to identify the nerves may be confusing to a nonanatomist.

Figure 27-2 is a fresh cadaveric tissue dissection showing the course of the brachial plexus from the interscalene to the infraclavicular area. However, the anatomic descriptive terms for the cords are based with the body in anatomic position and relative to its center; this is not descriptive of how the brachial plexus is encountered clinically. Many textbooks feature two-dimensional rather than three-dimensional diagrams of the plexus in this area, which contributes to the confusion. However, a solid understanding of the three-dimensional organization of the plexus may be the most important factor in successful blockade.

Figure 27-1. Organization of the brachial plexus.

Figure 27-2. Relationship of the brachial plexus, clavicle, and coracoid process.

Divisions, Branches, Cords, & Terminal Nerves

The anterior divisions of the upper (C5 and C6) and middle trunk (C7) unite to form the lateral cord, which lies lateral to the axillary artery and most superficial to the anterior chest skin. The anterior divisions of the lower trunk (C8 and Tl) form the medial cord. It lies medial to the axillary artery and is the deepest. The posterior cord is formed from all of the posterior divisions (C5 through Tl) and lies posterior to the artery just under the lateral cord. The cords end in terminal branches that are mixed nerves, which contain both sensory and motor components. They are the musculocutaneous, ulnar, median, axillary, and radial branches.

Other branches also exit the plexus prior to the formation of the terminal nerves. They are not mixed and are unique in that they are either sensory or motor nerves. These nerves are often not addressed but are important because the motor branches can be stimulated during performance of a block and knowing where they originate will help determine where to locate the tip of the needle. Tables 27–1 and 27–2 list the branches of the brachial plexus and their innervation.

Table 27–1.

Branches of Brachial Plexus

Table 27–2.

Terminal Nerves of Brachial Plexus

Note: All branches from the medial cord carry C8 and Tl fibers, and that of the higher spinal segments in the brachial plexus (C5 through C6) tend to innnervate muscles more proximal on the upper extremity, whereas the lower segments (C8, Tl) tend to innervate more distal muscles, such as those in the hand (Tl). Anatomic variation and the comingling of fibers from both lateral and medial cords makes it impossible to tell with certainty which cord is being stimulated with distal median nerve response.

CLINICAL ANATOMY

A simplified schematic diagram of the plexus is shown in Figure 27-1. This diagram depicts the plexus as it actually exists and a more clinical representation of how it is encountered when performing infraclavicular block. As shown, the posterior cord is not actually the most posterior cord but instead lies between the lateral and medial cords. The most helpful anatomic picture is in the sagittal plane as shown in Figure 27-3. This is a fresh cadaveric tissue dissection of the brachial plexus that was cut at the level of infraclavicular blockade to show this relationship. The relationship shown in this picture is helpful for guiding needle placement while performing this block. The sagittal view shown in Figure 27-4 illustrates the cords in a close up view surrounding the artery. Once this relationship is learned, the ability to change the needle directions for correct positioning is based on anatomy, and the need for subsequent passes to achieve successful placement lessens.

Figure 27-3. Relationship of the cords of the brachial plexus at the level of infraclavicular blockade to the subclavian/axillary artery.

Figure 27-4. Close-up view of the relationship of the cords of the brachial plexus at the level of infraclavicular blockade to the subclavian/axillary artery.

The cord that is most often encountered first when performing the infraclavicular block is the lateral cord because it is the most superficial. Just beyond the lateral cord is the posterior cord, which is in close proximity but just a bit deeper than the lateral cord. The medial cord is actually caudal or below the axillary artery, as can be seen in the sagittal picture in Figure 27-4. The schematic diagram of the cord shown in Figure 27-5 demonstrates the 90-degree angle of needle insertion for the lateral and posterior cord. This picture also illustrates the proximity of the artery and the risk of puncturing the artery when attempting to encounter the medial cord.

The Lateral Cord

The lateral cord supplies the lateral half of the median nerve and the musculocutaneous and the pectoral nerve branches (see Tables 27-1 and 27-2). This lateral portion of the median nerve is the motor innervation to the flexor muscles in the forearm, flexor carpi radialis, pronator teres (pronation of the forearm), and the thenar muscle of the thumb. It provides sensory innervation for the thumb to the lateral half of the fourth finger including the dorsal tips. The most distal motor response would be flexion of the fingers or flexion and opposition of the thumb.

Figure 27-5. Schematic of the relationship of the cords of the artery. brachial plexus to the subclavian/axillary artery.

Figure 27-6. Organization (A) and motor response (B) of the lateral cord.

The thumb has motor innervation from the ulnar nerve as well, which may be confusing if trying to interpret isolated thumb twitch. The ulnar nerve supplies the adductor pollicis, flexor pollicis brevis, and the first dorsal interosseous muscle. These muscles radially adduct the thumb. The flexor pollicis brevis assists in opposition of the thumb. The median nerve’s innervation of the flexor pollicis longus, abductor pollicis brevis, and the opponens pollicis are the major flexors for opposition of the thumb.

The musculocutaneous nerve has only muscular branches above the elbow and is purely sensory below the elbow as it becomes the lateral antebrachial cutaneous nerve. The motor response is flexion of the elbow by contraction of the biceps and sensation to the middle to median part of the forearm.

The anatomic relationship of the musculocutaneous nerve to the cords and the coracoid process is pertinent to infraclavicular block. It could be considered a branch because it exits early but it is more like a terminal nerve because it has sensory and motor innervations. The musculocutaneous nerve is encountered commonly in infraclavicular blockade because it often is outside of the cord in this area. Variations in brachial plexus anatomy are common. Because the musculocutaneous nerve most often exits the lateral cord quite early, the stimulation of this nerve is felt to be an unreliable indicator of stimulation of the lateral cord.¹⁷ This stimulation is not considered to be a distal response. It often overlies the lateral cord, which will be stimulated with deeper advancement of the needle as it passes the point of musculocutaneous nerve stimulation. Figure 27-6 depicts the lateral cord with its stimulated hand motor response.

The Posterior Cord

The posterior cord is just deep or inferior to the lateral cord. The axillary, the thoracodorsal, and upper and lower subscapular nerves are the branches from the posterior cord. They are involved in upper arm movement and shoulder movement and rotation as well as adduction of the shoulder and abduction of the arm. The branch most often encountered is the axillary nerve because it often has separated from the cord prior to the coracoid process. The axillary nerve to the deltoid elevates the upper arm. In addition to its branches, the posterior cord is responsible for the complete radial nerve. The distal responses from stimulation are abduction of the thumb and extension of the wrist and fingers (Figure 27-7). The brachioradialis muscle is innervated by the radial nerve and is classified as an extensor. Its stimulation should be characterized because it may be confused as a median nerve response because it actually flexes the elbow joint. Elbow flexion with radial deviation of the wrist represents stimulation of the brachioradialis muscle and a posterior cord response. The needle should be readjusted to obtain a more distal response of the radial nerve.

Figure 27–7. Organization (A) and motor response (B) of the posterior cord.

Figure 27–8. Organization (A) and motor response (B) of the medial cord.

The Medial Cord

The medial cord branches into the ulnar nerve and the medial half of the median nerve. Branches include the medial pectoral, medial brachial cutaneous, and the medial antebrachial cutaneous nerves. These branches innervate the skin of the anterior and medial surfaces of the forearm to the wrist. The ulnar nerve innervates half of the fourth and the fifth fingers, the adductor pollicis, and all interossei, which results in contraction of the fourth and fifth fingers and thumb adduction. Median nerve stimulation results in flexion and sensation of the first three and one half fingers, opposition of the thumb, and sensation of the palm (Figure 27-8).

Unlike the axillary block, responses to stimulation of the median nerve during infraclavicular block could conceivably arise from either cord. Classic studies of fiber topography of the median nerve by Sunderland identified pronator teres fibers and flexor carpi radialis in the lateral root, along with nerves to the flexor digitorum profundus, flexor pollicis longus, and intrinsic thenar muscles in the median root.¹⁸ Nerve injury studies also suggest that median fibers to the finger flexors are most likely found in the medial cord and medial root ofthe median nerve.¹՜ With the most commonly occurring plexus anatomy, finger flexion most likely identifies medial cord (or root) stimulation, but wrist flexion may result from either median or lateral cord (or root) stimulation.¹⁹ Tables 27–1 and 27–2 summarize the cords, branches, terminal nerves, and their motor stimulus response. Because of anatomic variability and the mixing of the median nerve between the medial and lateral cords, the same responses are listed for both nerves. Except in rare variants the ulnar nerve is carried within the medial cord.