Interscalene Brachial Plexus Block
An interscalene brachial plexus block is indicated for procedures involving the shoulder and upper arm. Roots C5 to C7 are most densely blocked, and the ulnar nerve originating from C8 and T1 may be spared. Therefore, interscalene blocks are not appropriate for surgery at or distal to the elbow. Contraindications include local infection, severe coagulopathy, local anesthetic allergy, and patient refusal. A properly performed interscalene block invariably blocks the ipsilateral phrenic nerve. Hemidiaphragmatic paresis may result in dyspnea, hypercapnia, and hypoxemia. Horner syndrome (myosis, ptosis, and anhidrosis) may result from proximal tracking of local anesthetic and blockade of sympathetic fibers to the cervicothoracic ganglion. Recurrent laryngeal nerve involvement often induces hoarseness. In a patient with contralateral vocal cord paralysis, respiratory distress may ensue. Other site-specific risks include vertebral artery injection (suspect if immediate seizure activity is observed), spinal or epidural injection, and pneumothorax.
Interscalene Brachial Plexus Block Techniques
Nerve stimulation: A relatively short (5-cm) insulated needle is usually used. Palpate the interscalene groove using the nondominant hand, pressing firmly to stabilize the skin against the underlying structures. Insert the block needle at an angle slightly medial and caudad and advance to optimally elicit a motor response of the deltoid or biceps muscles. A motor response of the diaphragm indicates that the needle is placed too anteriorly; a motor response of the trapezius or serratus anterior muscles indicates that the needle is placed too posteriorly. If bone (transverse process) is contacted, redirect more anteriorly. Aspiration of arterial blood should raise concern for vertebral or carotid artery puncture; the needle should be withdrawn, pressure held for 3 to 5 minutes, and landmarks reassessed.
Ultrasound technique: Identify the sternocleidomastoid and interscalene groove at the approximate level of C6; place the transducer perpendicular to the course of the interscalene muscles (“short axis”). The brachial plexus and anterior and middle scalene muscles should be visualized in cross-section. The brachial plexus at this level appears as three to five hypoechoic circles. The carotid artery and internal jugular vein may be seen lying anterior to the anterior scalene muscle. For an out-of-plane technique, insert the block needle just cephalad to the transducer and advance in a caudal direction toward the visualized plexus. After careful aspiration, local anesthetic (hypoechoic) spread should occur adjacent to (sometimes surrounding) the plexus. For an in-plane technique, insert the needle just posterior to the ultrasound transducer in a direction exactly parallel to the ultrasound beam. A longer block needle (8 cm) is usually necessary.
Supraclavicular Brachial Plexus Block
A supraclavicular brachial plexus block offers dense anesthesia of the brachial plexus for surgical procedures at or distal to the elbow. Historically, the supraclavicular block fell out of favor because of the high incidence of complications—namely, pneumothorax—with paresthesia and nerve stimulator techniques. It has seen resurgence in recent years because the use of ultrasound guidance has theoretically improved safety. The supraclavicular block does not reliably anesthetize the axillary and suprascapular nerves and thus is not ideal for shoulder surgery. Sparing of distal branches, particularly the ulnar nerve, may occur.
Around half of patients undergoing supraclavicular block experience ipsilateral phrenic nerve palsy, although this incidence may be decreased by using ultrasound guidance, allowing use of a minimal volume of local anesthetic. Horner syndrome and recurrent laryngeal nerve palsy may also occur. Pneumothorax and subclavian artery puncture, although theoretically reduced with ultrasound guidance, remain potential risks.
Supraclavicular Brachial Plexus Block Technique
Ultrasound technique: Position the patient supine with the head turned 30 degrees toward the contralateral side. Place a linear, high-frequency transducer in the supraclavicular fossa superior to the clavicle and angled slightly toward the thorax. The subclavian artery should be easily identified. The brachial plexus appears as multiple hypoechoic circles just superficial and lateral to the subclavian artery. The first rib should also be identified as a hyperechoic line just deep to the artery. Pleura may be identified adjacent to the rib and can be distinguished from bone by its movement with breathing.
For an out-of-plane technique, use a short, 22-gauge blunt-tipped needle. After anesthetizing the skin, insert the needle just cephalad to the ultrasound transducer in a posterior and caudad direction. After careful aspiration, inject 30 to 40 mL of local anesthetic in 5-mL increments while visualizing local anesthetic spread around the brachial plexus.
For an in-plane technique, a longer needle may be necessary. Insert the needle lateral to the transducer in a direction parallel to the ultrasound beam. Advance the needle medially toward the subclavian artery until the tip is visualized near the brachial plexus just lateral and superficial to the artery. Local anesthetic spread should be visualized surrounding the plexus after careful aspiration and incremental injection, which often requires injections in multiple locations and a highly variable volume (20–30 mL).
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