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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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To perform axillary block as effectively as possible, one must understand the organization of the peripheral nerves at the level of the lower axilla. It is clear that the axillary sheath at this level is discontinuous and may demand multiple injections to allow the axillary block to reach full effectiveness. This does not mean that a single injection cannot produce acceptable surgical anesthesia; however, the most consistently effective axillary block results from depositing smaller amounts of local anesthetic at multiple sites.

Another help when using a paresthesia-seeking axillary technique is to remember that a radial paresthesia is infrequently obtained. Thus, the anesthesiologist should not persist in attempting to produce one but, instead, inject the anesthetic in its expected position and let the local anesthetic volume produce the block. Furthermore, because the four-quadrant axillary approach uses a “field block” to anesthetize the musculocutaneous nerve, it also does not require a paresthesia to be effective. Because the median and ulnar nerves are more superficial when the arm is in an axillary block position, they are the nerves that a paresthesia is most likely to affect. Nevertheless, unnecessarily seeking a paresthesia for an extended time, even for median or ulnar sites, may result in anesthetic delays and patient discomfort, which may discourage anesthesiologists from carrying out this block. If one keeps in mind the quadrant approach to axillary block, the block should be accomplished in a time-efficient manner.

A useful mnemonic for remembering the position of the nerves at the level of the axillary block is “M&Ms are tops” (i.e., median and musculocutaneous nerves are more cephalad in the abducted arm). Everyone can relate the “top-notch” candy M&Ms to the cephalad position of the two “m” nerves.

When using a continuous catheter technique for postoperative analgesia or treatment of chronic pain patients, paying attention to securing the catheter helps prevent its unintentional removal. Also, the ability to place an infraclavicular catheter minimizes the number of axillary catheters needed in the anesthesiologist’s practice and is likely to improve her or his confidence when performing continuous brachial techniques.

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