Infraclavicular block

Placement

Anatomy. At the level of the proximal axilla, where the infraclavicular block is performed, the axilla is a pyramid-shaped space with an apex, a base, and four sides ( Fig. 8.1 A). The base is the concave armpit, and the anterior wall is composed of the pectoralis major and minor muscles and their accompanying fasciae. The posterior wall of the axilla is formed by the scapula and the scapular musculature, the subscapularis, and the teres major. The latissimus dorsi muscle abuts the teres major muscle to form the inferior aspect of the posterior wall of the axilla ( Fig. 8.1 B). The medial wall of the axilla is composed of the serratus anterior muscle and its fascia, and the lateral wall is formed by the converging muscle and tendons of the anterior and posterior walls as they insert into the humerus (see Fig. 8.1 B). The apex of the axilla is triangular and is formed by the convergence of the clavicle, the scapula, and the first rib. The neurovascular structures of the limb pass into the pyramid-shaped axilla through its apex ( Fig. 8.2 A).

The contents of the axilla are blood vessels and nerves—the axillary artery and vein and the brachial plexus, respectively—in addition to lymph nodes and loose areolar tissue. The neurovascular elements are enclosed within the anatomically variable, multipartitioned axillary sheath, a fascial extension of the prevertebral layer of cervical fascia covering the scalene muscles. The axillary sheath adheres to the clavipectoral fascia behind the pectoralis minor muscle and continues along the neurovascular structures until it enters the medial intramuscular septum of the arm ( Fig. 8.2 B).

The brachial plexus divisions become cords as they enter the axilla. The posterior divisions of all three trunks unite to form the posterior cord; the anterior divisions of the superior and middle trunks join to form the lateral cord; and the anterior division of the inferior trunk forms the medial cord. These cords are named according to their relationship to the second part of the axillary artery ( Fig. 8.3 ). From these cords nerves to the subscapularis, pectoralis major and minor, and latissimus dorsi muscles leave the brachial plexus. The medial brachial cutaneous, medial antebrachial cutaneous, and axillary nerves also leave the brachial plexus at the level of the cords.

At the lateral border of the pectoralis minor muscle (which inserts onto the coracoid process), the three cords reorganize to give rise to the peripheral nerves of the upper extremity. In a simplified scheme, the branches of the lateral and medial cords are all “ventral” nerves to the upper extremity. The posterior cord, in contrast, provides all “dorsal” innervation to the upper extremity. Thus the radial nerve supplies all the dorsal muscles in the upper extremity below the shoulder. The musculocutaneous nerve supplies muscular innervation in the arm and provides cutaneous innervation to the forearm. In contrast, the median and ulnar nerves are nerves of passage in the arm, but in the forearm and hand they provide the ventral musculature with motor innervation. These nerves can be further categorized: the median nerve innervates more heavily in the forearm, whereas the ulnar nerve innervates more heavily in the hand.

Position. The patient is placed supine, with the arm to be blocked abducted at the shoulder at a 90-degree angle if possible. If pain prevents this, the arm can be left at the patient’s side and adjustments can be made with skin markings. The anesthesiologist can stand on the ipsilateral or the contralateral side of the patient, depending on his or her preference and the patient’s body habitus. We prefer to stand on the ipsilateral side of the patient.

Traditional Approach. The coracoid process is identified by palpation and a skin mark placed at its most prominent portion. The skin entry mark is then made at a point 2 cm medial and 2 cm caudad to the previously marked coracoid process ( Fig. 8.4 A). Deeper infiltration is then performed with a 25-gauge, 5-cm needle while the needle is directed from the insertion site in a vertical parasagittal plane. Then a 7- to 9.5-cm, 20- to 22-gauge needle is inserted in a direction similar to that taken by the infiltration needle. If a paresthesia technique is used, a distal upper extremity paresthesia is sought; if a nerve stimulator technique is used, a distal upper extremity motor response is sought. If needle redirection is needed to achieve either a paresthesia or a motor response, the needle should be redirected only in a cephalocaudad arc ( Fig. 8.4 B). To avoid inadvertent entry into the thorax, it is important not to direct the needle path medially. The depth of contact with the brachial plexus depends on body habitus and needle angulation; it ranges from 2.5–3 cm in slender patients and from 8–10 cm in larger individuals.

Once adequate needle position has been achieved, either the single-injection dose of local anesthetic is administered incrementally, or 20 mL of preservative-free normal saline solution (5% dextrose if a stimulating catheter is used) is injected before threading the continuous brachial plexus catheter. For a single-injection technique, the block can be administered in a manner similar to that used in either a supraclavicular or an axillary block. For a continuous technique, we currently use a stimulating catheter device to optimize catheter placement.