Patient Selection

To undergo an axillary block, patients must be able to abduct the arm at the shoulder. As the experience of the operator increases, the need for abduction decreases, but this block cannot be carried out with the arm at the side. Because the block is most appropriate for forearm and hand surgery, it is a rare patient with a surgical condition at those sites who cannot abduct the arm as needed.

Pharmacologic Choice

Because hand and wrist procedures often require less motor blockade than procedures on the shoulder, the concentration of local anesthetic needed for axillary block can usually be slightly less than that needed for supraclavicular or interscalene block. Appropriate drugs are lidocaine (1% to 1.5%), mepivacaine (1% to 1.5%), bupivacaine (0.5%), and ropivacaine (0.5% to 0.75%). Lidocaine and mepivacaine produce 2 to 3 hours of surgical anesthesia without epinephrine and 3 to 5 hours with the addition of epinephrine. These drugs can be useful for less involved procedures or outpatient surgical procedures. For more extensive surgical procedures requiring hospital admission, a longer-acting agent such as bupivacaine can be chosen. Plain bupivacaine and ropivacaine produce surgical anesthesia that lasts from 4 to 6 hours; the addition of epinephrine may prolong this period to 8 to 12 hours. The local anesthetic timeline must be considered when prescribing a drug for outpatient axillary block because blocks lasting as long as 18 to 24 hours can result from higher concentrations of bupivacaine with added epinephrine. With continuous catheter techniques used for postoperative analgesia or chronic pain syndromes, 0.25% bupivacaine or 0.2% ropivacaine may be used, and even lower concentrations of these drugs may be used after a trial.

Anatomy

At the level of the distal axilla, where the axillary block is undertaken (Fig. 7-1), the axillary artery can be visualized as the center of a four-quadrant neurovascular bundle. I conceptualize these nerves in quadrants like a clock face because multiple injections during axillary block result in more acceptable clinical anesthesia 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 need to be performed in the axilla; in fact, needle insertion in the middle to lower portion of the axillary hair patch or even more distal to this 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 will help to decrease the number of unacceptable blocks performed. Also, this more distal approach to axillary block is similar to the mid-humeral brachial plexus block.

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

Position