Upper Extremity Peripheral Nerve Blocks: Interscalene Block

Interscalene Block

An interscalene brachial plexus block is indicated for procedures involving the shoulder and upper arm (Figure 46–8). Roots C5–7 are most densely blocked with this approach; and the ulnar nerve originating from C8 and T1 may be spared. There-fore, interscalene blocks are not appropriate for sur-gery at or distal to the elbow. For complete surgical anesthesia of the shoulder, the C3 and C4 cutane-ous branches may need to be supplemented with a superficial cervical plexus block or local infiltration.Contraindications to an interscalene block include local infection, severe coagulopathy, local anesthetic allergy, and patient refusal. A properly performed interscalene block invariably blocks the ipsilateral phrenic nerve (completely for nerve stimulation techniques; unclear for ultra-sound-guided techniques), so careful consideration should be given to patients with severe pulmonary disease or preexisting contralateral phrenic nerve palsy. The hemidiaphragmatic paresis may result in

dyspnea, hypercapnia, and hypoxemia. A Horner’s syndrome (myosis, ptosis, and anhidrosis) may result from proximal tracking of local anesthetic and blockade of sympathetic fibers to the cervico-thoracic 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 sei-zure activity is observed), spinal or epidural injec-tion, and pneumothorax. Even 1 mL of local anesthetic delivered into the vertebral artery may induce a seizure. Similarly, intrathecal, subdural, and epidural local anesthetic spread is possible.Lastly, pneumothorax is possible due to the close proximity of the pleura.

The brachial plexus passes between the anterior and middle scalene muscles at the level of the cricoid cartilage, or C6 ( Figure 46–9). Palpation of the inter-scalene groove is usually accomplished with the patient supine and the head rotated 30° or less to the contralateral side. The external jugular vein often crosses the interscalene groove at the level of the cricoid cartilage. The interscalene groove should not be confused with the groove between the sternoclei-domastoid and the anterior scalene muscle, which lies further anterior. Having the patient lift and turn the head against resistance often helps delineate the

anatomy. If surgical anesthesia is desired for the entire shoulder, the intercostobrachial nerve must usually be targeted separately with a field block since it originates from T2 and is not affected with an interscalene block. Interscalene perineural infusions provide potent analgesia following shoulder surgery.

A. Nerve Stimulation

relatively short (5-cm) insulated needle is usu-ally employed. The interscalene groove is palpated using the nondominant hand, pressing firmly to stabilize the skin against the underlying structures (Figure 46–10). After the skin is anesthetized, the block needle is inserted at a slightly medial and cau-dad angle and advanced to optimally elicit a motor response of the deltoid or biceps muscles (suggesting stimulation of the superior trunk). A motor response of the diaphragm indicates that the needle is placed in too anterior a direction; a motor response of the trapezius or serratus anterior muscles indicates that the needle is placed in too posterior a direction. If bone (transverse process) is contacted, the needle should be redirected more anteriorly. Aspiration of arterial blood should raise concern for vertebral or carotid artery puncture; the needle should be

withdrawn, pressure held for 3–5 min, and land-marks reassessed.

B. Ultrasound

A needle in-plane or out-of-plane technique may be used, and an insulated needle attached to a nerve stimulator can be used to confirm the accuracy of the targeted structure. For both techniques, after identification of the sternocleidomastoid muscle and interscalene groove at the approximate level of C6, a high-frequency linear transducer is placed perpendicular to the course of the interscalene mus-cles (short axis; Figure 46–11). The brachial plexus and anterior and middle scalene muscles should be visualized in cross-section (Figure 46–12). 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 ante-rior scalene muscle; the sternocleidomastoid is vis-ible superficially as it tapers to form its lateral edge.

For an out-of-plane technique, the block nee-dle is inserted just cephalad to the transducer and advanced in a caudal direction toward the visual-ized plexus. After careful aspiration for nonappear-ance of blood, local anesthetic (hypoechoic) spread

should occur adjacent to (sometimes surrounding) the plexus.

For an in-plane technique, the needle is inserted just posterior to the ultrasound transducer in a direc-tion exactly parallel to the ultrasound beam. A lon-ger block needle (8 cm) is usually necessary. It may be helpful to have the patient turn slightly laterally with the affected side up to facilitate manipulation of the needle. The needle is advanced through the middle scalene muscle until it has passed through the fascia anteriorly into the interscalene groove. The needle tip and shaft should be visualized during the entire block performance. Depending on visu-alized spread relative to the target nerve(s), a lower volume (10 mL) may be employed for postoperative analgesia, whereas a larger volume (20–30 mL) is commonly used for surgical anesthesia.