Describe the interscalene approach to blocking the brachial plexus.
The interscalene block can be achieved by either a pares-thesia or nerve stimulator technique. With the patient in the supine position, arms at the side and head turned to the contralateral side, the landmarks are identified. At the level of C6, the lateral border of the clavicular head of the stern-ocleidomastoid muscle is palpated. The fingers are then rolled posteriorly onto the belly of the anterior scalene muscle. The interscalene groove is located posterior to the anterior scalene muscle, between the anterior and middle scalene muscles, and is the point of needle insertion.
Using a 22G 2-inch insulated needle attached to a nerve stimulator, the skin is pierced at a 45° angle aiming toward the sternal notch. Proper positioning of the needle is determined by the detection of twitches of the triceps muscle and/or wrist movements when the nerve stimulator is at or below 0.4 mA. The local anesthetic preparation is injected, aspirating every 5 cc to avoid intravascular injec-tion of large amounts of local anesthetic. This block usually requires a volume of 40 cc of local anesthetic to be success-ful. A 1:1 mixture of mepivacaine 1.5% and bupivacaine 0.5% provides a quick onset of anesthesia and a block of long duration.