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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Anatomy.

At the level of the distal axilla, where the axillary block is undertaken ( Fig. 7-1 ), the axillary artery can be seen as indicating the center of a four-quadrant neurovascular bundle. I have found it useful to conceptualize these nerves in a quadrant or clockface manner because multiple injections during axillary block result in more acceptable clinical anesthesia in practice than does injection at a single site. The musculocutaneous nerve is found in the 9 to 12 o’clock quadrant in the substance of the coracobrachialis muscle. The median nerve is most often found in the 12 to 3 o’clock quadrant; the ulnar nerve is “inferior” to the median nerve in the 3 to 6 o’clock quadrant; and the radial nerve is located in the 6 to 9 o’clock quadrant. The block does not have to be performed in the axilla, and in fact needle insertion in the mid to lower portion of the axillary hair patch or even more distally is effective. It is clear from radiographic and anatomic study of the brachial plexus and the axilla that separate and distinct sheaths are associated with the plexus at this point. Keeping this concept in mind helps decrease the number of unacceptable blocks performed. Also, this more distal approach to the axillary block is similar to the mid-humeral brachial plexus block.

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Figure 7-1  Axillary block: functional “quadrant” anatomy of distal axilla.


Position.

The patient is placed supine, with the arm forming a 90-degree angle with the trunk and the forearm forming a 90-degree angle with the upper arm ( Fig. 7-2 ). This position allows the anesthesiologist to stand at the level of the patient’s upper arm and palpate the axillary artery, as illustrated in Figure 7-2 . A line should be drawn tracing the course of the artery from the mid-axilla to the lower axilla; overlying this line, the index and third fingers of the left hand of the anesthesiologist are used to identify the artery and minimize the amount of subcutaneous tissue overlying the neurovascular bundle. In this manner, the anesthesiologist can develop a sense of the longitudinal course of the artery, which is essential for performing an axillary block.

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Figure 7-2  Axillary block: position of the patient’s arm and palpation of the fingers.


Needle Puncture.

The axillary artery is identified with two fingers, and the needle is inserted as shown in Figure 7-3 . It must be emphasized that some local anesthetic should be deposited in each of the quadrants surrounding the axillary artery. If a paresthesia is obtained it is beneficial, although undue expenditure of time and patient discomfort should not occur in an attempt to elicit it. As illustrated in Figure 7-4 , an effective axillary block is achieved by utilizing the axillary artery as an anatomic landmark and infiltrating the tissue around it in a fan-like manner. Anesthesia of the musculocutaneous nerve is best achieved by infiltrating the coracobrachialis muscle. This maneuver can be carried out by identifying the coracobrachialis and injecting anesthetic into its substance or by inserting a longer needle until it contacts the humerus and then injecting the anesthetic in a fan-like manner near the humerus (see Fig. 7-4 ).

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Figure 7-3  Axillary block: needle insertion.


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Figure 7-4  Axillary block: fan-like injection using the axillary artery as a guide.


When using a continuous catheter technique for an axillary block, stimulating or nonstimulating catheter kits may be used, with my preference being the former ( Fig. 7-5 ). In the latter situation, the epidural needle is positioned with the assistance of either a nerve stimulator or paresthesia elicitation as an endpoint. After the needle is positioned, 20 mL of preservative-free normal saline solution is injected through the needle, and a catheter of appropriate size is inserted approximately 10 cm past the needle tip. Once the catheter has been secured with a plastic occlusive dressing, the initial bolus of drug is injected and the infusion started.

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Figure 7-5  Axillary block: continuous catheter technique after threading 10 cm of catheter proximally.


Potential Problems.

Problems with axillary block are infrequent because of the distance of this block from neuraxial structures and the lung. One complication, which can be minimized by using multiple injections rather than a fixed needle, is the occasional occurrence of systemic toxicity from the axillary block. Whenever a single, immobile needle is used to inject large volumes of a local anesthetic, the potential for systemic toxicity increases, especially in contrast with the use of smaller volumes of local anesthetic injected at multiple sites. Another potential problem with axillary block is the development of postoperative neuropathy, but one should not assume that axillary block is the cause of all neuropathy after upper extremity surgery. A logical and systematic approach to finding the cause of a neuropathy must be used if we are to understand the true incidence and causes of neuropathy after brachial plexus block and upper extremity surgery.

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