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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Anatomy.

Surface anatomy of importance to anesthesiologists includes that of the larynx, sternocleidomastoid muscle, and external jugular vein. Interscalene block is most often performed at the level of the C6 vertebral body, which is at the level of the cricoid cartilage. Thus, by projecting a line laterally from the cricoid cartilage, the level at which one should roll the fingers off the sternocleidomastoid muscle onto the belly of the anterior scalene and then into the interscalene groove can be identified. With firm pressure, it is possible to feel the transverse process of C6 in most individuals, and in some people it is possible to elicit a paresthesia by deep palpation. The external jugular vein often overlies the interscalene groove at the level of C6, although one should not rely on this feature ( Fig. 4-1 ).

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Figure 4-1  Interscalene block: surface anatomy.


It is always important to visualize what lies under the palpating fingers, and again the key to carrying out successful interscalene block is identifying the interscalene groove. Figure 4-2 allows us to look underneath the surface anatomy and develop a sense of how closely the lateral border of the anterior scalene muscle deviates from the border of the sternocleidomastoid. This feature should be constantly kept in mind. The anterior scalene muscle and the interscalene groove are oriented at an oblique angle to the long axis of the sternocleidomastoid muscle. Figure 4-3 removes the anterior scalene muscle and highlights the fact that at the level of C6 the vertebral artery begins its route to the base of the brain by traveling through the root of the transverse process in each of the more cephalad cervical vertebrae.

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Figure 4-2  Interscalene block: functional anatomy of scalene muscles.


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Figure 4-3  Interscalene block: functional anatomy of vertebral artery.


Position.

The patient lies supine with the neck in the neutral position and the head turned slightly opposite the site to be blocked. The anesthesiologist then asks the patient to lift the head off the table to tense the sternocleidomastoid muscle and allow identification of its lateral border. The fingers then roll onto the belly of the anterior scalene muscle and subsequently into the interscalene groove. This maneuver should be carried out in the horizontal plane through the cricoid cartilage—that is, at the level of C6. To roll the fingers effectively ( Fig. 4-4 ), the operator should stand at the patient’s side.

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Figure 4-4  Interscalene block technique: palpation.


Needle Puncture.

When the interscalene groove has been identified and the operator’s fingers are firmly pressing into the interscalene groove, the needle is inserted in a slightly caudal and slightly posterior direction, as shown in Figure 4-5 . As a further directional help, if the needle for this block is imagined as being quite long and if it is inserted deeply enough, it would exit the neck posteriorly in approximately the midline at the level of the C7 or T1 spinous process. If a paresthesia or motor repsonse is not elicited on insertion, the needle is walked along while maintaining the same needle angulation as shown in Figure 4-4 , in a plane joining the cricoid cartilage to the C6 transverse process. Because the brachial plexus traverses the neck at virtually a right angle to this plane, a paresthesia or motor response is almost guaranteed if small enough steps of needle reinsertion are carried out. When undertaking the block for shoulder surgery, this is probably the one brachial plexus block in which a large volume of local anesthetic coupled with a single needle position allows effective anesthesia. Hence, for shoulder surgery, 30 to 40 mL of lidocaine, mepivacaine, bupivacaine, or ropivacaine can be used. If the interscalene block is being carried out for forearm or hand surgery, a second, more caudal needle position is desirable, at which point 10 to 20 mL of additional local anesthetic is injected to allow spread along more caudal roots.

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Figure 4-5  Interscalene block technique: “paresthesia-seeking” plane.


Potential Problems.

Problems that can arise from interscalene block include subarachnoid injection, epidural block, intravascular injection (especially in the vertebral artery), pneumothorax, and phrenic block.

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