Infraclavicular brachial plexus block (ICB) is performed between the clavicle and axilla and can be used for surgical procedures performed below the midhumerus. Various ultrasound-guided ICB approaches have been reported.1, 2, 3 In Japanese regional anesthesia textbooks issued during the last decade, these approaches have commonly been classified as “distal” and “proximal.”4
In English literature, references to ultrasound-guided ICB generally indicate the distal approach. In this approach, an ultrasound transducer is placed near the coracoid process in the sagittal plane, and the distinct lateral, posterior, and medial brachial plexus cords, which surround the axillary artery, are visualized.1, 2 Multiple injections are recommended to ensure a block in all cords. However, controversy exists because a single injection posterior to the axillary artery has been demonstrated to provide a more reliable blockade in comparison with multiple injections into the three distinct cords.5 All three cords are not always identifiable by ultrasonography in the distal approach because of their variable and relatively deeper locations. We presume that this difficulty in identification may affect the manner of insertion in the distal approach. Furthermore, the appropriate catheter tip position for a continuous block is also controversial, although tip placement near the posterior cord is suggested.2
In the proximal approach, which is frequently described in Japanese literature, the linear transducer is placed adjacent to the inferior border of the clavicle, parallel to the clavicle, and lateral to the midclavicular line.4 As the transducer is moved from the distal approach position to this position, the cords become relatively superficial and cluster laterally to the first part of the axillary artery. Accordingly, multiple injections toward each cord are unnecessary in the proximal approach. A needle is inserted laterally to medially toward the clustered cords, in plane with the transducer. All three cords can be blocked by a single local anesthetic injection. The goal of the continuous ICB using the proximal approach is to place the catheter tip near the clustered cords (Video 1). A potential disadvantage of the proximal approach is a risk of pneumothorax because the pleura are closer to the brachial plexus, compared with the distal approach. However, this concern might be obviated if the needle is constantly visualized under ultrasound guidance. A needle can be visualized more easily in the proximal approach than in the distal approach because the target is located more superficially in the former. Furthermore, the reduced number of needle passes in the proximal approach may decrease the incidence of inadvertent vessel punctures and nerve injuries.
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In contrast to Japanese literature, the English literature has rarely described a proximal-level technique for ultrasound-guided ICB. The medial infraclavicular technique is a type of proximal-level technique for ICB.3 In this technique, a microconvex transducer is placed at the apex of the deltopectoral groove in the sagittal plane; the target is to group the brachial plexus cords close together, superior to the axillary artery. The puncture is made immediately inferior to the clavicle, in the superior-to-inferior direction, and needle insertion angles are steeper than in the proximal approach. A costoclavicular approach for ultrasound-guided ICB, similar to the proximal approach with respect to transducer position and needle trajectory, was recently reported.6 In our practice, the proximal approach is performed with the blocked-side arm abducted 90°; by contrast, the aforementioned report did not mention the arm position during the costoclavicular approach.6Abducting the arm moves the brachial plexus away from the thorax and closer to the dermal surface3 because the pectoralis major muscle, which is located superficial to the brachial plexus and the axillary artery, is stretched by the arm abduction, as Figure 1 demonstrates. Furthermore, this position elevates the clavicle slightly in the cephalad direction. By contrast, with arm adduction, the clavicle occasionally interferes with sufficient proximal transducer placement where the cords are clustered. Figure 1 shows the transducer positions and ultrasound images acquired via the proximal approach. The dotted line on the patient indicates the inferior clavicle border with the arm adducted to the side (Figure 1A), and the solid line indicates the same element with the arm abducted 90° (Figure 1B). Clavicle elevation allows a more proximal placement of the transducer along the axillary artery and facilitates clear visualization of the cords, although the ideal angles of arm abduction should be validated in a future study.
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We believe that, compared with the distal approach, the proximal approach for ultrasound-guided ICB is promising with respect to the reduced number of needle passes and the effectiveness of continuous block; therefore, we encourage a future randomized controlled trial.