Interscalene Brachial Plexus Block

Ultrasound guidance for accurately depositing local anesthetic at the level of the cervical roots and trunks of the brachial plexus has many advantages secondary to the abundance of vascular, neurological, and pleural structures that may be entered inadvertently using blind techniques. An easy method of identifying and then following the brachial plexus at this level starts by first visualizing the subclavian artery (SA) immediately posterior to the clavicle by holding the probe between the base of the neck and the clavicle (Fig. 21.3). The probe is then moved from lateral to medial until the pulsation of the SA is visualized. Further medial movement also brings the subclavian vein (SV) into view and its junction with the innominate vein.

Figure 21.3 Photograph demonstrating suggested initial ultrasound probe position for ultrasound-guided interscalene block.
Figure 21.4 Ultrasound image demonstrating anatomy of the supraclavicular brachial plexus. The arrow identifies the nerve plexus and A indicates the subclavian artery.

Once the SA is seen, the brachial plexus can be easily seen as a group immediately lateral to the artery (Fig. 21.4).

Once visualizing the brachial plexus in the supraclavicular region, it becomes straightforward to trace the anatomical structures to find the interscalene brachial plexus. The easiest way to do this is to follow the anterior scalene muscle as it passes first medial and then over the SA. The anterior scalene muscle is then followed more cephalad into the neck and the brachial plexus trunks followed by the brachial plexus roots can be seen lying anterior to the scalenus medius muscle and posterior to the anterior scalene muscle. A transverse view of the interscalene brachial plexus is demonstrated in Fig. 21.5a.

Another method of finding the interscalene brachial plexus is to hold the ultrasound probe in the horizontal plane at the laryngeal or cricoid level (transverse process of C6). The

Figure 21.5a Interscalene brachial plexus and its anatomical relations as seen with ultrasound in the transverse plane. ASM anterior scalene muscle, CA carotid artery, RIJ right internal jugular vein, arrows identify the roots/trunks of the brachial plexus and the target for deposition of local anesthetic.

Figure 21.5a Interscalene brachial plexus and its anatomical relations as seen with ultrasound in the transverse plane. ASM anterior scalene muscle, CA carotid artery, RIJ right internal jugular vein, arrows identify the roots/trunks of the brachial plexus and the target for deposition of local anesthetic.

probe is inclined somewhat caudad to produce an ultrasound beam that cuts across the roots of the brachial plexus that inclines inferiorly and anteriorly from their origin at the transverse processes. The most recognizable structure anteriorly is the pulsatile common carotid artery (CA) and its companion internal jugular (IJ) vein usually anterior and lateral to the carotid. The IJ may be collapsed or vary in diameter with respiration. The sternocleidomastoid muscle (SCM) is a characteristic muscular structure (hypoechoic with striations) just deep to the subcutaneous layer with a tapered posterior edge, and the anterior and middle scalene muscles are deep to the SCM and posterior to the CA. The cervical roots of C5 through C7 are oligofascicular and hypoechoic round or oval structures which become apparent with slight changes in the caudad inclination of the probe or with movement of the probe in the cephalad or caudad direction (Fig. 21.5b).

Ultrasound-guided interscalene block is most easily performed using the transverse view of the brachial plexus. The roots and trunks of the brachial plexus can be seen stacked from lateral to medial with the C5-C6 roots or superior trunk visible most laterally. The needle can be advanced either in-plane or out-of-plane with the probe. The needle tip can be placed within the interscalene groove in order to obtain local anesthetic spread around the brachial plexus. The in-plane approach permits the needle shaft to be visualized throughout insertion using a posterior approach to the plexus in the long axis and is the most commonly preferred technique (Figs. 21.3 and 21.5b).

An indwelling PNB catheter technique is possible using the described method, but catheter fixation may be somewhat more difficult than that of an infraclavicular technique (described below). Using a Tuohy needle, a catheter can be inserted 1-2 cm past the needle tip, initial local anesthetic bolus given, and infusion initiated. "Hydrodissection" may be accomplished prior to catheter placement by local anesthetic administration through the Tuohy needle under ultrasound in order to visualize the local anesthetic spread within the plexus. A common side effect of this PNB technique is the occurrence of Horner's syndrome secondary

Figure 21.5b Interscalene block. Interscalene brachial plexus and its anatomical relations as seen with ultrasound in the transverse plane. Interscalene anatomy in the transverse plane at the C6 level with the needle (in-line) identifying the plexus. 1 sternocleidomastoid muscle, 2 anterior scalene muscle, 3 middle scalene muscle, 4 internal jugular vein, 5 carotid artery, arrows aimed at trunks of brachial plexus.

Figure 21.5b Interscalene block. Interscalene brachial plexus and its anatomical relations as seen with ultrasound in the transverse plane. Interscalene anatomy in the transverse plane at the C6 level with the needle (in-line) identifying the plexus. 1 sternocleidomastoid muscle, 2 anterior scalene muscle, 3 middle scalene muscle, 4 internal jugular vein, 5 carotid artery, arrows aimed at trunks of brachial plexus.

to the proximity of the sympathetic chain at this level. In addition, phrenic nerve blockade may be as frequent as 100%. Other potential complications include infection, hematoma, local anesthetic toxicity, patient discomfort, neurologic injury, and failed block.

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