Section 3: Anesthesia Management
Part C: Anesthesia Techniques
Chapter 43: Nerve Blocks

Peripheral Blocks at the Elbow and Wrist

Clinical Applications

As techniques for brachial plexus blockade have gained popularity, indications for peripheral nerve blockade at the wrist and elbow have diminished. However, these techniques can be useful when limited anesthesia is required, when contraindications to brachial plexus block (e.g., infection, bilateral surgery, coagulation abnormalities, bleeding diasthesis, difficult anatomy) exist, or when brachial plexus blockade is incomplete.

Peripheral nerve blocks do not provide anesthesia for the use of a tourniquet. Most patients tolerate an inflated tourniquet for only a brief period.

A midhumeral approach to the brachial plexus has been described. This novel approach involves blocking each nerve separately in the humeral canal. Blockade of the four major nerves of the upper extremity at the midhumeral level using a peripheral nerve stimulator has been reported to have a higher success rate than traditional (defined as stimulation of two nerves) axillary brachial plexus block. 28  In this study, time to complete the block did not differ between the two techniques; however, onset of complete sensory block was shorter in the axillary approach, whereas the success rate of blockade of all four major nerves was higher in the midhumeral group. This technique may have applications when anatomic difficulties preclude a traditional approach or when the surgical procedure requires a dense block of all four major nerves. The safety and clinical practicality of the midhumeral approach remain to be proven.

Side Effects/Complications

In general, distal peripheral blocks are associated with a lower risk of complications. However, intravascular injection can occur, and the usual precautions of incremental injection after aspiration are recommended. The risk of nerve injury is theorized to be higher when more distal peripheral blocks are performed. This may be due to superficial nerve placement between bony and ligamentous structures, thereby offering ready access to the probing needle point.

Elbow Versus Wrist

The forearm cutaneous nerves arise in the upper arm and are not anesthetized by block of the peripheral nerves at the elbow. Hence, there is no advantage of block of the peripheral nerves of the upper extremity when comparing elbow with wrist techniques; both provide sensory anesthesia of the hand.

Median Nerve

Block of the median nerve provides anesthesia of the palmar aspects of the thumb and index finger, middle finger and radial half of the ring finger, and the nail beds of the same digits. Motor block includes the muscles of the thenar eminence, lumbric muscles of the first and second digits, and, in the case of the block at the elbow, median-innervated wrist flexor muscles of the forearm.

Technique at the Elbow

With the patient‘s arm placed in the anatomic position (palm up), a line is drawn connecting the medial and lateral epicondyles of the humerus. The major landmark for this technique is the brachial artery, which is found medial to the biceps tendon at the intercondylar line. The median nerve lies medial to the artery (Fig. 43–8) and can be blocked with 3 to 5 mL of solution after eliciting a paresthesia. If no paresthesia is obtained, the solution can be injected fanwise medial to the palpated artery.

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FIGURE 43–8 Anatomic landmarks for median and radial nerve block at the elbow.

Technique at the Wrist

The median nerve is located between the flexor carpi radialis and palmaris longus tendons and can be blocked at a point 2 to 3 cm proximal to the wrist crease (Fig. 43–9). (The palmaris longus tendon is congenitally or postsurgically absent from some patients.) A loss of resistance is felt as the needle passes through the flexor retinaculum, at which point 2 to 4 mL of solution should be injected. A superficial palmar branch supplying the skin of the thenar eminence can be blocked by injecting 0.5 to 1 mL of solution subcutaneously above the retinaculum. Paresthesias should not be sought because of the confinement of this nerve within the carpal tunnel.

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FIGURE 43–9 Anatomic landmarks for median and ulnar nerve block at the wrist. An alternative method for ulnar nerve block, from the ulnar side of the wrist, is shown.

Radial Nerve

Block of the radial nerve provides anesthesia to the lateral aspect of the dorsum of the hand (thumb side) and the proximal portion of the thumb, index, middle, and lateral half of the ring fingers.

Technique at the Elbow

The radial nerve can be blocked at the elbow as it passes over the anterior aspect of the lateral epicondyle. The intercondylar line and lateral edge of the biceps tendon are marked. A 22-gauge, 3- to 4-cm needle is inserted at a point 2 cm lateral to the biceps tendon and is advanced until bone is encountered (see Fig. 43–8) . A fanwise injection is made using 3 to 5 mL of solution.

Technique at the Wrist

The radial nerve block at the wrist is a field block of the multiple peripheral branches descending along the dorsum and radial side of the wrist. The extensor pollicis longus tendon can be identified when the patient extends the thumb. The needle insertion is over this tendon at the base of the first metacarpal; the injection is superficial to the tendon. Two milliliters of local anesthetic is injected proximally along the tendon, and an additional 1 mL is injected as the needle passes at a right angle across the “anatomic snuffbox” (Fig. 43–10).

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FIGURE 43–10 Anatomic landmarks and method of needle insertion for radial nerve block at the wrist.

Ulnar Nerve

Blockade of the ulnar nerve provides anesthesia of the ulnar side of the hand, the little finger, and the ring finger and all the small muscles of the hand, except those of the thenar eminence and the first and second lumbric muscles.

Technique at the Elbow

Although the ulnar nerve is easily accessible at its subcutaneous position posterior to the medial epicondyle, blockade at this site is associated with a high incidence of neuritis. The nerve is surrounded by fibrous tissue at this point, requiring an intraneural injection for successful blockade. Use of a very fine needle along with a small volume of solution (1 mL) diminishes the risk; however, the nerve can be satisfactorily blocked with 5 to 10 mL of solution at a site 3 to 5 cm proximal to the elbow. The local anesthetic should be injected in a fanwise fashion without elicitation of a paresthesia.

Technique at the Wrist

At the wrist, the ulnar nerve lies beneath the flexor carpi ulnaris tendon between the ulnar artery and the pisiform bone. At this point, it has already given off its palmar cutaneous and dorsal branches. The nerve can be approached by directing the needle medially from the radial side of the tendon or, alternatively, by directing the needle radially from the ulnar side of the tendon (see Fig. 43–9). After eliciting a paresthesia, 3 to 5 mL of solution is injected or spread in a fanwise fashion.

Musculocutaneous Nerve

The musculocutaneous nerve terminates as the lateral cutaneous nerve of the forearm. This nerve provides sensory innervation to the skin on the radial side of the forearm up to the radiocarpal joint. This block is usually performed to supplement the axillary approach to brachial plexus anesthesia.

Technique at the Elbow

The lateral cutaneous nerve of the forearm can be blocked 1 cm proximal to the intercondylar line immediately lateral to the biceps tendon. Fanwise infiltration of 3 to 5 mL of solution subcutaneously at this site provides excellent anesthesia of this nerve.