Patient Position: Supine, with ipsilateral arm abducted 120° with the elbow flexed 90°. This position rotates the plexus away from the pleura and closer to the surface of the skin.
Indications: Elbow, forearm, or hand surgery.
Needle Size: 50-mm, 22-gauge needle.
Surface Landmarks: Clavicle and deltopectoral groove. Skin over the pectoralis major muscle.
Ultrasonographic Landmarks: Note the pectoralis major and minor muscles, and the clavipectoral fascia immediately deep to the pectoralis minor muscle (Fig. 35-1). The axillary artery and axillary vein lie just beneath the clavipectoral fascia. Adjacent to the artery are found the cords of brachial plexus: the lateral cord (cephaloanterior), posterior cord (cephalad), and medial cord (cephaloposterior). The pleura and second or third rib are seen deep to the axillary artery, vein, and plexus (Fig. 35-1).
Transducer Position: In sagittal plane with the probe positioned 1 cm below the clavicle and 1 to 2 cm medial to the deltopectoral groove.
Volume: 15 to 20 mL.
Technique: Sterile prep of skin. Place a sterile cover over the probe or sterilize the probe itself. Use sterile ultrasound gel on the field. Subcutaneous local anesthetic is injected at the superior margin of the transducer. The block needle is inserted at this site, at a 45° angle, and advanced in-plane parallel to the long axis of the transducer, so that the entire needle remains in view on the ultrasound machine screen. The steep downward angle makes keeping the needle image intact on the screen more challenging than with more superficial nerves. The needle is directed toward the cords in sequence, and as each cord is contacted, the peripheral nerve stimulator is turned on, with current set to 0.5 to 1 mA, if stimulation is desired for confirmation. When sensory or motor stimulation confirms the appropriate cord has been contacted, local anesthetic is delivered in small aliquots, observing spread of local anesthetic around each cord and any branches. This confirms that the needle tip is not intravascular. For contact of the medial cord, wrist or finger flexion, with ulnar deviation, is typical, as is thumb adduction. When the lateral cord is contacted, wrist or finger flexion, or elbow flexion, is expected. Finally, for stimulation of the posterior cord, elbow, wrist, or finger extension is typical. At each cord, 5 mL of local anesthetic is injected in small increments, creating a “halo” around each one.
Figure 35-1. a, axillary artery; BP, brachial plexus; c, clavicle; L, lung; LC, lateral cord; MC, medial cord; PC, posterior cord; pm, pectoralis minor; v, axillary vein.
1. Innervation patterns vary and stimulation may vary from the classic patterns described for the three cords. In addition, some patients have only two cords, or very rarely, one cord.
2. Some authors have reported good results for ultrasound guided infraclavicular block by simply delivering a circumferential bolus of local anesthetic around the entire axillary artery.
3. Note that the artery is usually cephalad to the vein. It may be difficult to collapse the vein with chest wall pressure, due to its depth. Color-flow Doppler can be helpful to distinguish the two vessels, along with changes in caliber of the vein with respiration. Both the artery and vein give rise to small branches at this level, and it is imperative to look for these with ultrasound as well as aspirating frequently during local anesthetic injection.
4. The pleura and lung are only a few millimeters deep to the posterior cord and vessels. Care must be taken to keep the tip of the needle in view with ultrasound at all times in order to avoid pneumothorax.
5. Some authors advocate visualizing the cords and delivering local anesthetic to each without stimulation.
6. If the patient's upper extremity is fractured, or if the patient's shoulder is frozen, the block can be performed with the patient's upper extremity adducted to the side. The probe and needle approach are the same as described above.
7. Some practitioners prefer to perform the block at a more distal position along the plexus. In this case the probe should be placed inferior to the coracoid process. The plexus lies deeper here and may be more difficult to visualize. In this location, the medial cord may lie posterior to the axillary artery, or may be sandwiched in between the axillary artery and vein (Fig. 35-2).
Figure 35-2. a, axillary artery; cn, cutaneous nerve; m, median nerve; pma, pectoralis major; pmi, pectoralis minor; LC, lateral cord; mc, musculocutaneous nerve; MC, medial cord; PC, posterior cord; r, radial nerve; u, ulnar nerve; V, axillary vein.
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