Chapter 8 – Distal Upper Extremity BlocksULNAR, MEDIAN, AND RADIAL BLOCK AT THE ELBOW Perspective
In general, distal upper extremity blocks—those at the elbow or wrist—are not strongly encouraged. Although definitive data are lacking, there is a perception that these more distal peripheral blocks are associated with a slightly higher likelihood of nerve injury. This is perhaps because many of the peripheral branches are anatomically located in sites where the nerve is contained within bony and ligamentous surroundings. It is not difficult to localize the nerves at these peripheral sites, although the “entrapment” of these nerves makes more proximal blocks (e.g., the axillary block) my preferred approach. Furthermore, because a significant portion of hand and forearm surgery is carried out using an upper arm tourniquet, purposeful use of more distal blocks mandates significantly heavier sedation so the patient can tolerate more tourniquet inflation pressure.Patient Selection.
Few patients should require distal upper extremity block, although some may need it, such as those who require supplementation after brachial plexus block. In any event, these patients should be few in number, and comprehensive anesthesia care should be possible without frequent use of these blocks.Pharmacologic Choice.
These peripheral blocks are usually considered for superficial surgery; thus, lower concentrations of local anesthetic are appropriate because motor blockade should not be an issue. Therefore 0.75% to 1% mepivacaine or lidocaine, 0.25% bupivacaine, or 0.2% ropivacaine should be sufficient.Placement At the Elbow Anatomy.
Of the three major nerves at the elbow—radial, median, ulnar—the ulnar nerve is most predictable in terms of location. As illustrated in Figure 8-1 , the ulnar nerve is located in the ulnar groove, which is a bony fascial canal between the medial epicondyle of the humerus and the olecranon process. This area is extremely well protected by fibrous tissue; and despite what seems like an easy site to carry out a block, the nerve is quite well protected (and potentially vulnerable) in the ulnar groove. The median nerve at the elbow lies medial to the brachial artery, which lies just medial to the biceps muscle. Conversely, the radial nerve has a somewhat variable course; it pierces the lateral intramuscular septum on its way to the forearm and lies between the brachialis muscle and the brachioradialis muscle in the distal aspect of the upper arm. It is more effectively blocked in the axilla than at the elbow.
All three of these nerves are blocked with the patient in the supine position and the arm supinated and abducted at the shoulder at a 90-degree angle. Additionally, when the ulnar nerve block is performed, the forearm is flexed on the upper arm to identify the ulnar groove more easily (see Figure 8-3 ).
A line should be drawn between the medial and the lateral epicondyles of the humerus (at the level of the pane of glass shown in Figure 8-1 ). Immediately medial to the brachial artery, the needle is inserted in the plane of the “pane of glass,” and a paresthesia is sought. If no paresthesia is obtained, injection of 3 to 5 mL of solution medial to the brachial artery should result in a median nerve block. If a paresthesia is obtained, a similar amount is injected at that site.
The radial nerve is likewise blocked at the level of the “pane of glass” seen in Figure 8-1 . The biceps tendon at that level should be identified, and a mark then made 1 to 2 cm lateral to the tendon. A small-gauge, 3-cm needle is inserted through the mark in the plane of the “pane of glass,” and a paresthesia is sought. If no paresthesia is obtained, a fan-like injection of 4 to 6 mL of solution is made at that site.Needle Puncture: Ulnar Nerve Block.
As illustrated in Figure 8-3 , the forearm is flexed on the upper arm, and the ulnar groove is palpated. At a point approximately 1 cm proximal to a line drawn between the olecranon process and the medial epicondyle, a needle is inserted. A paresthesia should be easily obtainable; and once it is, the needle is withdrawn 1 mm. At this point, 3 to 5 mL of local anesthetic is injected through a small-gauge, 2-cm needle. A larger volume of solution should not be injected directly into the ulnar groove, as high pressure in this tightly contained fascial space may increase the risk of nerve injury.At the Wrist Anatomy ( Fig. 8-4 ).
The ulnar nerve lies immediately lateral to the tendon of the flexor carpi ulnaris muscle and immediately medial to the ulnar artery. The median nerve lies between the tendon of the palmaris longus and the tendon of the flexor carpi radialis muscle. That places the median nerve in the long axis of the radius. The radial nerve at the wrist has already divided into a number of its peripheral branches, and effective radial block requires a field block along the radial aspect of the wrist.
To achieve a peripheral block at the wrist, the patient rests supine while the arm is extended at the shoulder and supported on an arm board. The wrist is flexed over a small support, and the anesthesiologist most effectively stands in the long axis of the arm board. While performing the block in that position, the anesthesiologist may observe the patient’s face during elicitation of a paresthesia.
It should be easy to palpate the tendon of the flexor carpi ulnaris and the ulnar artery immediately proximal to the ulnar styloid process. A small-gauge, short-bevel needle can be inserted perpendicular to the wrist at this site, and a paresthesia should be easy to elicit. Anesthetic solution (3–5 mL) can be injected at this site; if no paresthesia is obtained, a similar amount can be injected in a fan-like manner between those two structures with near certainty of the block.Needle Puncture: Median Nerve Block.
The palmaris longus tendon and the tendon of the flexor carpi radialis are identified on a line between the styloid process of the ulna and the prominence of the distal radius. These tendons can be accentuated by having the patient flex the wrist while making a fist. The median nerve lies deep and between those structures, so a blunt-beveled, small-gauge, short needle is inserted between the tendons. If a paresthesia is obtained, 3 to 5 mL of anesthetic solution is injected; if no paresthesia is obtained, a similar amount is injected in a fan-like manner between the two tendons.Needle Puncture: Radial Block.
Blocking the radial nerve at the wrist requires infiltrating its multiple peripheral branches, which descend along the dorsal and radial aspect of the wrist. A field block is performed at the subcutaneous level in and around the anatomic “snuff box.” The injection should be carried out superficial to the extensor pollicis longus tendon, which is easily identified by having the patient extend the thumb. This block may require 5 to 6 mL of local anesthetic and is an infrequently used technique.Potential Problems.
As outlined, problems with the peripheral blocks primarily involve the potential for compression nerve injury and the suggestion of a slightly increased incidence of neuropathy. Theoretically, this occurs because of the tight fascial compartments in which these nerves run through the distal arm, forearm, and wrist. Likewise, blocking these distal nerves does not allow tourniquet use, which is often the clinical limiting factor.Pearls
Suggestions for the successful use of these blocks involve avoiding them when possible. Understanding the concepts outlined for axillary nerve block should make the need of these blocks infrequent.