Interscalene block (classic anterior approach) is especially effective for surgery of the shoulder or upper arm because the roots of the brachial plexus are most easily blocked with this technique. Frequently the ulnar nerve and its more peripheral distribution in the hand can be spared, unless one makes a special effort to inject local anesthetic caudad to the site of the initial paresthesia. This block is ideal for reduction of a dislocated shoulder and often can be achieved with as little as 10–15 mL of local anesthetic. This block also can be performed with the arm in almost any position and thus can be useful when brachial plexus block needs to be repeated during a prolonged upper extremity procedure.
Patient Selection. Interscalene block is applicable to nearly all patients because even obese patients usually have identifiable scalene and vertebral body anatomy. However, interscalene block should be avoided in patients with significantly impaired pulmonary function. This point may be moot if one is planning to use a combined regional and general anesthetic technique, which allows intraoperative control of ventilation. Even when a long-acting local anesthetic is chosen for the interscalene technique, usually phrenic nerve, and thus pulmonary function will return to a level that patients can tolerate by the time the average-length surgical procedure is completed.
Pharmacologic Choice. Useful agents for interscalene block are primarily the amino amides. Lidocaine and mepivacaine provide surgical anesthesia for 2–3 hours without epinephrine and for 3–5 hours when epinephrine is added. These drugs can be useful for less complex or outpatient surgical procedures. For more extensive surgical procedures requiring hospital admission, longer-acting agents such as bupivacaine or ropivacaine can be chosen. The more complex surgical procedures on the shoulder often require muscle relaxation; thus bupivacaine concentrations of at least 0.5% are needed. Plain bupivacaine produces surgical anesthesia lasting from 4–6 hours; the addition of epinephrine may prolong this to 8–12 hours. Ropivacaine’s effects are slightly shorter in duration.
Traditional block technique
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. 5.1 ).
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. Fig. 5.2 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. Fig. 5.3 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.
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 and subsequently into the interscalene groove. This maneuver should be carried out in the horizontal plane through the cricoid cartilage—thus at the level of C6. To roll the fingers effectively the operator should stand at the patient’s side ( Fig. 5.4 ).
Needle Puncture. When the interscalene groove has been identified and the operator’s fingers are firmly pressing in it, the needle is inserted, as shown in Fig. 5.5 , in a slightly caudal and slightly posterior direction. As a further directional help, if the needle for this block is imagined to be long and 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 response is not elicited on insertion, the needle is “walked” while maintaining the same needle angulation as shown in Fig. 5.4 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. For shoulder surgery 25–35 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, in which 10–15 mL of additional local anesthetic is injected to allow spread along more caudal roots.