UPPER EXTREMITY CONDUCTION BLOCKS

Anatomic Considerations

Sensory and motor innervation of the upper extremity is almost exclusively supplied by the brachial plexus, which is formed by the union of the ventral rami of the fifth cervical to the first thoracic spinal nerves within the interscalene space (see Chapter 44 ). Originally, three trunks (i.e., superior, middle, and inferior) are formed. When these trunks exit the interscalene groove, they reach the subclavian artery and are cephaloposterior to it; they then split and redistribute the nerve fibers to three cords (i.e., lateral, posterior, and medial) that surround the axillary artery. The brachial plexus is enveloped by a continuous sheath derived from the deep cervical fascia and the fascias from the scalene muscles; a single injection within this envelope produces complete plexus blockade by blocking the trunks (i.e., supraclavicular approaches) or the cords (i.e., infraclavicular approaches, including axillary blocks). Because of the presence of a transverse barrier at the level of the coracoid process of the scapula, supraclavicular and axillary blocks are not equivalent, and the nerves leaving the brachial plexus above this limit (i.e., suprascapular, axillary, and in one half of patients, musculocutaneous nerves) are not anesthetized by axillary blocks. Commonly used supraclavicular approaches include the interscalene, parascalene, and perisubclavian approaches. Infraclavicular approaches consist mainly of coracoid and axillary approaches. A humeral approach as described in adults^[200] can be used in adolescents but does not offer significant advantages over the classic axillary approaches that are far easier to perform.