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It is great to have an extra arrow in your quiver when it comes to regional anesthesia of the upper extremity. There are instances where a supra or infraclavicular block may be impossible or difficult. Infection, dressing, implanted device or catheter at site of injection may be prohibitive. These blocks may be technically difficult due to patient habitus, patient cooperation, or inability for optimal positioning. The supraclavicular block is a very reliable, relatively easy block to perform. However, in certain populations there is concern with phrenic nerve palsy (although less with ultrasound and low volume local anesthetics). Patients occasionally complain about the extent of numbness and paralysis of the arm and shoulder, especially after hand surgery. The infraclavicular block may remedy some of these concerns but is technically more challenging. The needle is more difficult to visualize because of the steep angle to the probe. There is also a higher risk of pneumothorax.
One option to consider is an ultrasound guided axillary nerve block. Advantages include no risk of pneumothorax or phrenic nerve palsy and the site is easily compressible if bleeding occurs. Since this block is at the level of the terminal branches, it may be useful as a “rescue block” where a specific branch would be targeted. It is also a very superficial block at this location allowing superb visualization of structures and your needle. There is, however, more anatomic variation at this level making it less reliable than supra and infraclavicular block - especially for surgical anesthesia.
The optimal position is a supine patient with operative limb abducted to 90 degrees and externally rotated. An arm table is useful for this position. Standard monitors, supplemental oxygen and sedation of choice are provided. Sitting at the head of the bed, the operator should place a linear transducer perpendicular to the axillary artery. The needle will enter in a cephalocaudad direction, through the biceps and toward the triceps. At this level the main terminal branches (Radial, Median and Ulnar) should be visible surrounding the artery. On the way to the axillary sheath, the musculocutaneous nerve can be targeted. It is surprisingly easy to see between the biceps and coracobrachialis muscles. It is sometime embedded within the coracobrachialis muscle. After 5-7cc of local is injected here, continue to the axillary sheath. While all branches should be within the sheath it is prudent to inject aliquots in four quadrants surrounding the artery. Although more time consuming, these branches have motor innervation so a nerve stimulator can be used for identification.
This technique is only indicated for surgeries below the elbow. It will not reliably cover tourniquet pain. For cutaneous coverage of the upper arm, one would need to supplement the intercostobrachial and medial brachial cutaneous nerves.
There are great tutorials and pictures available on-line at WWW.NYSORA.COM
Big Sur - photo by JoAnn Sturman
