4 Interscalene Block
Traditional Block Technique
Placement
Anatomy
Surface anatomy of importance to anesthesiologists includes 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, one can identify 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. When firm pressure is applied, in most individuals it is possible to feel the transverse process of C6, 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 this should not be relied on (Fig. 4-1).
It is important to visualize what lies under the palpating fingers; again, the key to carrying out successful interscalene block is the identification of the interscalene groove. Figure 4-2 allows us to look beneath surface anatomy and develop a sense of how closely the lateral border of the anterior scalene muscle deviates from the border of the sternocleidomastoid muscle. 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 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.