This article, an excerpt from our eBook “Ultrasound-Guided Regional Anesthesia” by Dr. Brandon Winchester, co-founder of blockjocks.com, discusses the approaches and anatomy of an ultrasound-guided axillary block.
The axillary block is the most distal brachial plexus block. It targets the terminal branches of the brachial plexus: look for the musculocutaneous, radial, median, and ulnar nerves.
Why Axillary Nerve Blocks?
The axillary block can be used for forearm, hand, or wrist surgery. It is useful for pulmonary patients since it spares the phrenic nerve. It is also useful for morbidly obese patients. The chest wall and the neck can be very thick in larger patients.
The axilla (the location of the axillary block) is actually quite superficial even if:
- You have a larger patient and scan the supraclavicular region with ultrasound, it’s going to be deep.
- You scan the infraclavicular region, it’s going to be even deeper. For example, if you do a single shot block for wrist surgery and the patient is obese, the axillary block is going to be the easiest of the three blocks to complete.
Ultrasound Guided Approach
Envision the axillary block positioning like a clock face. Consider the axillary artery the clock and the musculocutaneous, median, ulnar, and radial nerves as targets (the numbers) aligned around the clock face.
The musculocutaneous nerve is the furthest away from the axillary artery and is located in the eight o’clock position, therefore one must target the musculocutaneous separately. Once you have targeted and injected local anesthetic around the musculocutaneous nerve, you should essentially encircle the axillary artery to numb the remaining three nerves.
Encircle Two Structures
The simplest way to do an axillary block is to encircle the two structures: the musculocutaneous nerve and the axillary artery. There is some variability from patient to patient where the median, ulnar, and radial nerves exist relative to the axillary artery, but you can be confident they are covered if you encircle the axillary artery. Using this technique will give you a high level of confidence that you have completed this block successfully.
Choosing a Brachial Plexus Block for Non-Shoulder Upper Extemity Surgery
There is a common false paradigm that all surgeons and anesthesiologists have been taught at some point in their career: upper extremity surgeries such as the proximal arm are better performed with nerve blocks of the upper part of the brachial plexus, such as the supraclavicular nerve block. While distal surgeries such as finger and wrist surgery are better performed with distal blocks such as axillary blocks. This is simply not true. In fact, the supraclavicular, infraclavicular, and axillary blocks can be used for each for these purposes interchangeably.
A study compared the supraclavicular, infraclavicular, and axillary blocks for elbow surgery and lower. The study examined how much time it took to complete each block, the comfort level of the patient during each block, and the success rate of each block (how successful they achieved surgical anesthesia). The results showed each block took relatively the same amount of time, the patients pain levels were all low, and they each achieved a 95% success rate and up¹.
Not Recommended for Nerve Block Catheters
The axillary block is not a recommended location to place continuous nerve block catheters because there are several surrounding vessels in the area. This is not a concern if the initial injection is done while the patient is being monitored; the issue is leaving a catheter near or through a vessel.
You do not want to risk sending a patient home with local anesthesia infusing into the bloodstream. The nerves in this particular block are very spread out; leaving a catheter in place involves a single catheter opening that is infusing local anesthesia into a single location. It is very difficult to reach all four nerves with a single catheter location.
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1.Tran, D., Russo, G., Muñoz, L., Zaouter, C., & Finlayson, R.(2009).A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks.NCBI.Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/19574871