Ultrasound-Guided Brachial Plexus Block in Infants and Children

David P. Martin

Joseph D. Tobias

Stephen Lucas

Sunathenam Suresh

Paul E. Bigeleisen

The brachial plexus originates from the C5 through T1 nerve roots. It is anatomically divided into trunks, divisions, cords, and ultimately into the terminal branches. The brachial plexus is responsible for the complete sensory and motor innervation of the arm, except the upper half of the medial and posterior part of the arm, which is innervated by the intercostobrachial nerve, a branch of T2. The brachial plexus can be anesthetized by the deposition of local anesthetic agents at one of several locations along the plexus (interscalene, parascalene, supraclavicular, infraclavicular, or axillary approach).¹^,² Although the axillary approach was previously the most commonly used technique to anesthetize the brachial plexus, the use of ultrasound has allowed practitioners to use more proximal blocks safely and often with significantly less local anesthetic agent. The advent of ultrasound has revolutionized the practice of brachial plexus anesthesia, allowing the various approaches in even our youngest patients. An interscalene approach is used for procedures involving the shoulder, and surgery of the upper extremity distal to the shoulder or the midhumerus can be performed with a supraclavicular or infraclavicular approach. As with most regional anesthesia that is performed in infants and children, brachial plexus anesthesia is most frequently used as an adjunct to anesthesia with the block placed after the induction of anesthesia either at the start or completion of the surgical procedure.³ In these cases, the block is used to provide postoperative analgesia. In other circumsTances, brachial plexus blockade can be used instead of general anesthesia to provide surgical anesthesia or even occasionally as a therapeutic modality whereby the sympathetic blockade that accompanies the motor and sensory blockade is used to improve regional blood flow.⁴^, ⁵^, ⁶^and ⁷ Although many practitioners advocate the use of only ultrasound for brachial plexus anesthesia, the use of a nerve stimulator combined with ultrasound is advocated by some as a means of further localizing the blockade of the plexus to only the desired region. For specific clinical scenarios, the nerve stimulator and low volumes of a local anesthetic agent can be used to provide selective blockade of specific nerves of the plexus.

Axillary approach to the brachial plexus

Background and Indications: The terminal branches of the brachial plexus (musculocuTaneous, median, radial, and ulnar nerves) arise from the cords relatively high in the axilla. The musculocuTaneous nerve is identified as an oval hyperechoic structure cephalad to the artery, lying between the biceps and coracobrachialis muscles. The median, radial, and ulnar nerves or the cords that give rise to them may have variable positions around the artery (Fig. 40.1). Although there is often wide anatomical variation in the location of the cords or terminal branches of the brachial plexus, typical locations in relation to the axillary artery are as follows: (1) the median nerve lies anteriorly, (2) the radial nerve lies inferolateral to the artery, and (3) the ulnar nerve lies anteromedial to the artery. These three nerves appear as hyperechoic
clusters around the artery. The cuTaneous nerves often have the same appearance, although depending on the size of the patient, it may not be possible to identify these nerves. In many cases, the outlines of the nerves become apparent as the local anesthetic solution is injected. In children, it may be possible to anesthetize the axillary nerve as well as the radial nerve by injecting local anesthetic posterior to the axillary artery when the block is performed high in the axilla. Local anesthetic injected using an axillary approach in small children frequently spreads cephalad. Thus, the axillary nerve is often blocked when local anesthetic is injected around the radial nerve. A selective musculocuTaneous nerve block is usually required with the axillary approach as the nerve is outside the fascial sheath that encases the other nerves. This can be performed by identification of the musculocuTaneous nerve within the body of the coracobrachialis muscle. The musculocuTaneous nerve provides innervation to the lateral aspect of the forearm. Depending on the site of surgery, axillary block may be sufficient for anesthesia of the upper arm, forearm, and hand in small children. If a tourniquet is used, some practitioners perform a separate subcuTaneous injection along the upper medial aspect of the arm just below the axilla to anesthetize the intercostobrachial nerve, which is a branch of the second intercostal nerve. This may help to delay the onset of tourniquet pain, although there is no evidence for this practice. One of the major limitations of this approach is that it cannot be performed in patients who cannot abduct their arm due to pain or restricted mobility while they are awake (Fig. 40.2).

Figure 40.1. Photograph showing optimal positioning of the patient and probe placement for using ultrasound-guided approach to the brachial plexus at the axilla. The patient is positioned supine with the arm abducted 90 degrees from the body and the elbow flexed 90 degrees.

Patient position: Supine with arm abducted 90 degrees from the body and the elbow flexed 90 degrees.

Transducer: 25-mm linear array oscillating at 8 to 13 MHz.

Transducer orientation: Transverse in the axilla.

Needle: 22G or 24G, 1- or 2-inch, blunt or insulated needle.

Local anesthetic: The volume is dependent on the size of the patient, and the concentration is dependent on the degree of motor blockade that is desired. For postoperative
analgesia, 0.25% bupivacaine or 0.2% ropivacaine are effective, whereas 0.5% concentrations of either are used to provide surgical anesthesia and profound motor blockade. In most patients, a total volume of 0.2 to 0.3 mL/kg is sufficient. Because of the precise targeting of the nerves, only small amounts of local anesthetic are required for each nerve target. In all cases, the total dose of bupivacaine or ropivacaine should be ≤3mg/kg. Epinephrine in a concentration of 1:200,000 is added to the solution to identify inadvertent systemic injection.

Figure 40.2. Ultrasound image of the axillary approach to the brachial plexus demonstrating the orientation of the four nerves around the axially artery. At this level, the musculocuTaneous nerve is generally outside of the sheath and difficult to anesthetize unless a separate injection is performed. AA, axillary artery; BC, biceps brachii muscle; CB, coracobrachialis muscle; H, humerus; MC, musculocuTaneous nerve; MN, median nerve; PEC MAJOR, pectoralis major muscle; PEC MINOR, pectoralis minor muscle; RN, radial nerve; UN, ulnar nerve.

Technique: For the axillary approach, the patient’s arm is abducted 90 degrees from the body and the elbow is flexed at a 90-degree angle so that the hand is above the level of the head or behind it. For ultrasound-guided blockade of the axillary plexus, after the axilla is washed with a sterile prep solution, sterile ultrasound gel is placed and the ultrasound probe is inserted into a sterile cover. A high-frequency ultrasound probe is oriented in the transverse plane quite high in the axilla with the axillary artery centered on the screen. If the procedure is performed without the use of general anesthesia, local anesthesia is provided by subcuTaneous infiltration with a 27G needle. The block needle is inserted in line, cephalad to the probe and directed toward the musculocuTaneous nerve. The nerve is surrounded with a small volume of the local anesthetic agent (2 to 3 mL). The needle is then withdrawn to a position just below the skin and directed toward the median nerve. An injection of 2 to 4 mL of local anesthetic, depending on the size of the patient, is made until the nerve is surrounded; the needle is then advanced in the same plane targeting the ulnar nerve, and the injection process is repeated. Lastly, the needle is withdrawn and redirected inferiorly to the artery, targeting the radial nerve and local anesthetic is injected. In some patients, the artery must be pushed out of the way of the needle to reach all four nerves through the same injection site. If slightly larger volumes are injected around the radial nerve, the axillary nerve is usually blocked if the needle insertion site is in the proximal axilla.

Interscalene approach to the brachial plexus

Background and Indications: Prior to the introduction of ultrasound for regional anesthe sia, interscalene blocks were used less frequently in children because of the potential for adverse effects including pneumothorax, vascular puncture, and neuraxial spread of local anesthetic. As the trunks of the brachial plexus are organized in a superior-to-inferior direction between the anterior and middle scalene muscles, the lower dermatomes of the brachial plexus may be less effectively blocked than with more distal approaches.⁸ Therefore, the term ulnar sparing has been used to describe the relative lack of reliable blockade of the caudal or lower components of the brachial plexus. The relative degree of ulnar sparing may be reduced with the use of ultrasound because the disTance anatomically between the interscalene and more distal access point to the brachial plexus is quite small.⁹ The ultrasound shortens the disTance because an optimal picture for the interscalene approach is obtained more distal than where the landmarks for a blind technique would dictate. In addition to the risks of pneumothorax, vertebral artery puncture with local anesthetic toxicity is of particular concern. The vertebral artery provides direct blood flow to the central nervous system, thus even minute amounts of local anesthetic agents can lead to seizures in the event of arterial injection. Due to the proximity of the vertebral column and spinal cord, there is also a potential for epidural or intrathecal injection. These aforementioned risks are purportedly increased with a blind, nerve-stimulator approach, and the risk of such complications should be decreased by the use of ultrasound and direct visualization of the site of local anesthetic placement.¹⁰ Additional issues include blockade of surrounding nerves resulting in phrenic nerve blockade with hemidiaphragm paralysis, recurrent laryngeal nerve block with unilateral vocal cord paralysis, and sympathetic block with Horner syndrome.¹¹^,

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