Chapter 31. Cutaneous Blocks for the Upper Extremity

Although most upper extremity regional anesthesia is accomplished by means of various approaches to the brachial plexus, there are occasions when individual terminal nerves or their branches are blocked selectively. There are generally three instances in which the anesthesiologist desires to perform these selective nerve blocks. First, some surgical sites are partially innervated by sensory nerves that are not part of the brachial plexus or not consistently anesthetized with plexus blocks. This chapter describes how and when to anesthetize the most common of these nerves—the supraclavicular, the suprascapular, and the intercostobrachial. The second indication is when blocking the entire brachial plexus block is not necessary for the planned procedure. In this case, selective upper extremity cutaneous anesthesia or analgesia may involve blocking terminal nerves (radial, median, or ulnar nerves) or their branches (lateral and medial antebrachial cutaneous nerves) distally at the elbow. A final and controversial indication for selective upper extremity nerve blocks is their use as a supplement to an incomplete brachial plexus block.

This chapter discusses individual nerve blocks as a means of furthering the reader's understanding of the indications and contraindications for selective upper extremity regional anesthesia. When considering the application of these various blocks, the reader is reminded that innervation of the upper extremity is often variable and overlapping.1 Therefore, when faced with the choice of performing a single nerve block versus blocking several adjacent nerves, it is advisable to err on the side of multiple blocks, particularly in those adjacent cutaneous areas that represent potential crossover innervation (Figures 31–1 and 31–2). The relevant anatomy will be covered with specific nerve block description.

Local Anesthetic & Adjuvant Selection

Local anesthetics for individual upper extremity nerve blocks are selected for their desired duration of anesthesia and/or analgesia. If intermediate-acting local anesthetics are selected (lidocaine or mepivacaine), duration can be increased with either adjuvant epinephrine (2.5 mcg/mL) or clonidine (0.5 mcg/kg). Neither adjuvant significantly increases duration when a long-acting local anesthetic such as bupivacaine or ropivacaine is chosen.1

Indications

The supraclavicular nerve provides sensory innervation to the “cape” of the shoulder (Figure 31–3). Commonly anesthetized as a component of cervical plexus block for carotid surgery, the supraclavicular nerve may also require blockade for surgery involving the shoulder or supraclavicular area. Local anesthetic spread in an interscalene approach to brachial plexus block is often adequate to block the supraclavicular nerve, but the nerve is frequently not anesthetized with a supraclavicular brachial plexus block. Particularly in patients undergoing supraclavicular or incomplete interscalene brachial plexus anesthesia without concomitant general anesthesia, the supraclavicular nerve can be blocked to accomplish more complete anesthesia for shoulder surgery.

Anatomy

The supraclavicular nerve is derived from the ventral rami of the third and fourth cervical nerve roots (C3-C4); it is thus separate from the brachial plexus. The nerve becomes superficial as it penetrates the mid-belly of the sternocleidomastoid muscle, thereafter forming three branches (Figure 31–3). These branches provide sensory innervation to the cape area, which spans from the midline to the deltoids, and from the second rib anteriorly to the top of the scapula posteriorly.

Technique

Blockade of the supraclavicular nerve is accomplished with 10 mL of an intermediate or long-acting local anesthetic, depending on analgesic requirements. Three milliliters are deposited with a 22- to 25-gauge sharp needle into the mid-belly of the sternocleidomastoid muscle. The remaining volume of local anesthetic is then injected subcutaneously in a cephalad and caudad direction along the posterior border of the sternocleidomastoid (Figure 31–4).

Complications

Complications of the supraclavicular nerve block are minimal provided that aseptic technique is used and local anesthetic injection remains superficial. The external jugular vein should be avoided to prevent hematoma.

Indications

Suprascapular nerve block (SSNB) can be used as an adjunct to arthroscopic shoulder surgery and total shoulder arthroplasty. When combined with general anesthesia for shoulder arthroscopy, SSNB improves analgesia, reduces opioid-related side effects, and hastens hospital discharge,2 although SSNB is not superior to interscalene block in this setting.3 For anterior open shoulder surgery, supplemental SSNB does not affect outcome when combined with interscalene block.4 Because it provides major sensory innervation to the shoulder joint, it can be used to block supplementally the suprascapular nerve for analgesia after total shoulder arthroplasty. Furthermore, because it may send branches to the anterior axilla, the suprascapular nerve may require supplementation to anesthetize the anterior arthroscopic port site in awake patients who receive an interscalene block as the sole anesthetic for surgery.

Anatomy

The suprascapular nerve (C4-C5) branches from the superior trunk of the brachial plexus and therefore is usually anesthetized by an interscalene block. It traverses the suprascapular notch and continues laterally along the superior border of the scapular spine (Figure 31–5). The supraclavicular nerve provides sensory innervation to 70% of the posterior-superior shoulder joint, the acromioclavicular joint, and a portion of the anterior axilla in up to 10% of patients.1 The suprascapular nerve provides motor innervation to the supraspinatus and infraspinatus muscles, but minimal if any cutaneous innervation over the scapula or posterior shoulder.

Technique

Surface landmarks are identified by drawing one line along the superior border of the scapular spine and then bisecting it with a second line drawn parallel with the vertebral spine. From where these two lines cross, the suprascapular notch underlies a point ∼2–3 cm toward the middle of the upper/outer quadrant (see Figure 31–5). A 1.5-in. 22-gauge needle is placed at this entry mark and directed caudad in the parasagittal plane until it contacts the scapular spine, followed by injection of 10 mL of a long-acting local anesthetic. If a peripheral nerve stimulator is used, the suprascapular nerve is identified by the motor response of external shoulder rotation.

Complications

Pneumothorax can result from a needle that passes through the suprascapular notch and enters the pleural space. This complication is largely avoidable by directing the needle in a caudad, rather than anterior, direction.

Indications

The intercostobrachial nerve block is indicated for surgery involving the medial/posterior upper arm and/or for anterior arthroscopic port placement. A secondary indication is to alleviate the sensation resulting from a pneumatic tourniquet applied to the upper arm. Despite a commonly held misperception, the intercostobrachial nerve block does not block the ischemic, compressive components that cause tourniquet pain. Rather, the intercostobrachial nerve block simply blocks the cutaneous sensation associated with tourniquet inflation.

Anatomy

The intercostobrachial nerve arises from the second thoracic (T2, and occasionally T1) nerve root (see Figure 31–2). As such, it is not a component of the brachial plexus and is therefore not anesthetized by any brachial plexus approach. Along with the medial cutaneous nerve of the arm (an intermediary branch of the medial cord), the intercostobrachial nerve provides cutaneous sensation to the upper half of the medial/posterior arm. It also innervates a portion of the anterior axilla (see Figures 31–1 and 31–2).

Technique

Anesthetizing the intercostobrachial nerve involves simply depositing a subcutaneous line of local anesthetic superiorly and inferiorly along the axillary crease. Three to five milliliters of local anesthetic are injected via a 1.5-in. 25-gauge needle (Figure 31–6).

Complications

Because of its superficial placement, complications of the intercostobrachial nerve block are virtually nonexistent.

Indications

Local anesthetic blockade of the lateral and medial antebrachial cutaneous nerves is indicated for superficial surgery of the forearm, such as arteriovenous fistula surgery, or as a supplement to incomplete brachial plexus block.

Anatomy

The lateral antebrachial cutaneous nerve of the forearm (LAC) is the primary cutaneous branch of the musculocutaneous nerve. It provides cutaneous innervation to the lateral (radial) half of the volar forearm. The medial antebrachial cutaneous nerve of the forearm (MAC) is an intermediary branch of the medial cord. It provides cutaneous innervation to the medial (ulnar) half of the volar forearm, an area commonly misperceived as innervated by the ulnar nerve (see Figures 31–1 and 31–2).

Technique

Considering the unpredictable overlap of forearm cutaneous innervation, it is advisable to perform both LAC and MAC nerve blocks when forearm anesthesia is desired. Blocking the LAC is accomplished with two local anesthetic injections placed along the intercondylar line. The first 5 mL of local anesthetic are injected just deep to the lateral margin of the biceps tendon; the second 5 mL area injected subcutaneously and lateral from the first injection site, along the elbow crease (Figure 31–7). The MAC is blocked by injecting a half-ring of 5–7 mL local anesthetic about a quarter of the arm's length above the medial elbow. When LAC and/or MAC nerve blocks are supplemental to a previous incomplete brachial plexus block, the additional 15–20 mL of local anesthetic should be well tolerated by patients if injected 20–30 minutes after the primary block.5

Complications

Techniques for anesthetizing the LAC and MAC nerves involve only superficial injection of local anesthetic; thus the risk of nerve injury is very low. For this reason, these blocks may be preferable to selective elbow or wrist blocks as a supplement to incomplete brachial plexus anesthesia involving the volar forearm cutaneous distribution.

Indications

Proximal techniques of brachial plexus block are often superior to selective nerve block at the elbow because the latter are more difficult to perform, are more time-consuming and uncomfortable, and potentially carry a greater risk of complications. For instance, the anesthesiologist who desires to provide selective analgesia strategies to specific terminal nerves may be better served by the midhumeral brachial plexus block, where selective application of clonidine6 or low concentration of a long-acting local anesthetic7 to the median and ulnar nerves prolongs analgesia without concomitant prolongation of motor block. Another reason to avoid selective elbow blocks is the commonly misunderstood cutaneous innervation of the forearm. For example, block of the musculocutaneous nerve must be performed in the axilla to render motor block of the biceps and brachioradialis muscles. But anesthetizing the cutaneous distribution of the musculocutaneous nerve is best accomplished with a LAC nerve block. Anesthetizing the skin of the medial forearm requires blockade of the MAC nerve, not the ulnar nerve at the elbow. A third issue is to avoid elbow blocks to supplement incomplete brachial plexus blocks because this practice theoretically increases the risk of anesthesia-related nerve injury. Indeed, the only indication for elbow approaches is to block forearm flexor and extensor muscles when the surgeon desires immobility of the fingers.

Radial Nerve Block

Anatomy

The radial nerve supplies sensation to the dorsum of the forearm and hand (see Figures 31–1 and 31–2); it also innervates the musculature of the dorsal forearm. The radial nerve descends the posterior arm, traversing from the medial to the lateral side. At the epicondyles, the radial nerve lies relatively deep between the brachialis and brachioradialis muscles (Figure 31–8).

Technique

The patient is positioned supine for radial nerve block with the arm supinated and abducted. Selective block of the radial nerve is accomplished by placing a needle ∼1.5 cm lateral to the biceps tendon at the level of the epicondyles (see Figure 31–8). Three to five milliliters of local anesthetic are injected when a paresthesia to the hand is elicited. If using a peripheral nerve stimulator, one seeks the motor response of wrist extension.

Median Nerve Block

Anatomy

The median nerve provides sensation to the radial palm, the proximal fingers from the thumb to the long finger, and motor control to the forearm flexors (see Figures 31–1 and 31–2). It passes the elbow joint just medial to the brachial artery and in front of the brachialis muscle.

Technique

Median nerve block at the elbow is accomplished with a 1.5-in. needle that is placed just medial to the brachial artery at the level of the epicondyles (see Figure 31–8). Either a motor response that consists of wrist flexion and/or thumb opposition, or a paresthesia to the thumb or index finger, is sought before injecting 3–5 mL of local anesthetic.

Ulnar Nerve Block

Anatomy

The ulnar nerve at the elbow is located superficially in the ulnar groove (Figure 31–9). At this level, blockade of the ulnar nerve results in anesthesia of the little finger and motor block of the intrinsic muscles of the hand.

Technique

The patient is placed supine for ulnar nerve block and the forearm is flexed at the elbow (see Figure 31–9). After identification of the ulnar groove, a short needle is placed ∼1 cm proximal to the epicondyles and directed distally. The desired endpoint is paresthesia to the little finger or a motor response consisting of finger flexion, thumb adduction, and/or ulnar deviation of the wrist. It is suggested that only 2–3 mL of local anesthetic be injected to avoid excessive pressure within the tight fascial space of the ulnar groove and thereby lessen the possibility of compromising neural blood flow.

Complications

Selective nerve blocks at the elbow may rarely cause hematoma. However, it is the potential for anesthesia-related nerve injury that adds risk when these blocks are used to supplement incomplete proximal brachial plexus block. This theoretical risk is based on the concept that needle placement in the vicinity of nerves that already have full or partial proximal local anesthetic blockade may reduce the patient's ability to perceive a paresthesia or pain on injection. Although not conclusively proven, these fears are nevertheless based on reported perioperative nerve injuries that occurred in the setting of supplementation.1 Conversely, supplemental injections placed within a brief time (≤5 minutes) from initial injection of local anesthetic may carry less risk.8

Because cutaneous nerve blocks of the upper extremity require only small amounts of local anesthetic, which are typically injected subcutaneously and not proximate to major vessels, they can be placed with minimal monitoring and should require little postoperative observation. However, if these blocks are placed in conjunction with major plexus blocks, then full monitoring and recovery monitoring are required. Because most of the nerves considered in this chapter have insignificant motor innervation, prolonged motor block leading to positioning injuries is seldom a consideration. Nevertheless, outpatients should be warned to protect their insensate limbs from external pressure or temperature extremes.

Selective upper extremity nerve blocks can be useful supplements to brachial plexus blocks. Supraclavicular, suprascapular, and superficial cutaneous nerve blocks are valuable adjuncts to the anesthesia and/or analgesia primarily provided by a plexus block or general anesthesia. The LAC and MAC nerve blocks can provide either primary anesthesia for superficial forearm operations or supplement an incomplete plexus block. Selective elbow blocks are inferior alternatives to brachial plexus blocks. Their use as a supplement to incomplete plexus blockade should be practiced with caution.