Chapter 12

• Indications: shoulder, arm, and elbow surgery
• Landmarks: the clavicular head of the sternocleidomastoid muscle, clavicle, external jugular vein
• Nerve stimulation: twitch of the pectoralis, deltoid, arm, forearm, or hand muscles at 0.2–0.5 mA
• Local anesthetic: 25–35 mL
• Complexity level: intermediate

###### Figure 12-1.

Needle insertion for interscalene brachial plexus block. The needle is inserted between palpating fingers that are positioned in the scalene groove (between anterior and middle scalene muscles). 1 = sternal head of the sternocleidomastoid muscle. 2 = clavicular head of the sternocleidomastoid muscle.

An interscalene block relies on the spread of a relatively large volume of local anesthetic within the interscalene groove to accomplish blockade of the brachial plexus. In our practice, we almost always use a low interscalene block technique, which consists of inserting the needle more caudally than in the commonly described procedure performed at the level of the cricoid cartilage. Our reasoning is that at the lower neck, the interscalene groove is more shallow and easier to identify, and the distribution of anesthesia is also adequate for elbow and forearm surgery. In addition, the needle insertion is more lateral, which makes puncture of the carotid artery less likely and performance of the block easier to master by trainees. Low approach to interscalene block is used in shoulder, arm, and forearm surgery. In our practice, the most common indications for this procedure are shoulder and humerus surgery and the insertion of an arteriovenous graft for hemodialysis.

The brachial plexus supplies innervation to the upper limb and consists of a branching network of nerves derived from the anterior rami of the lower four cervical and the first thoracic spinal nerves. Starting from their origin and descending distally, the components of the plexus are named roots, trunks, divisions, cords, and, finally, terminal branches. The five roots of the cervical and the first thoracic spinal nerves (anterior rami) give rise to three trunks (superior, middle, and inferior) that emerge between the medial and anterior scalene muscles to lie on the floor of the posterior triangle of the neck (Figure 12-2). The roots of the plexus lie deep to the prevertebral fascia, whereas the trunks are covered by its lateral extension, the axillary sheath. Each trunk divides into an anterior and a posterior division behind the clavicle, at the apex of the axilla (Figure 12-3). The divisions combine to produce the three cords, which are named lateral, median, and posterior according to their relationship to the axillary artery. From this point on, individual nerves are formed as these neuronal elements descend distally (Figure 12-3 and Table 12-1).

###### Figure 12-2.

Anatomy of the brachial plexus. The sternocleidomastoid muscle is removed and the brachial plexus is seen emerging between the scalene muscles. ...

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