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).

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.

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.

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,