|Level of blockade||Coverage distribution (Figure 136-1)|
|Branches of the brachial plexus: median, ulnar, and radial nerves + musculocutaneous (outside the “sheath”)|
- Median nerve
- Ulnar nerve
- Radial nerve
- Musculocutaneous nerve (blocked separately)
Board question: which nerve is not blocked by the axillary block? A: the axillary nerve!
And also the musculocutaneous nerve, which has to be blocked separately.
Typical arrangement of nerves around the axillary artery in the axilla (Figure 136-2).
Variations (Figure 136-3).
Figure 136-1. Distribution of Blockade Following Performance of an Axillary Block
NB: An intercostobrachial block is typically added, which will cover the medial aspect of the elbow and arm.
Figure 136-2. Typical Arrangement of the Nerves Around the Axillary Artery in the Axilla
MC, musculocutaneous nerve (in the coracobrachialis muscle); M, median nerve; U, ulnar nerve, R, radial nerve; T, branches to the triceps muscle; CB, intercostobrachial nerves.
Figure 136-3. Variations in the Position of the Nerves
MC, musculocutaneous nerve; M, median nerve; U, ulnar nerve; R, radial nerve; *: branch to the triceps (from radial nerve);**: intercostobrachial nerves; arrowhead: needle insertion from the medial aspect of the arm. Adapted from Partridge BL, Katz J, Benirschke K. Functional anatomy of the brachial plexus sheath: implications for anesthesia. Anesthesiology. 1987;66:743–747.
Upper extremity surgery, preferably below the elbow, as the level of the block is not always adequate for elbow surgery, or for a very proximal tourniquet.
None besides the usual regional anesthesia contraindications.
- Landmarks: the axillary artery pulse as proximal as possible in the axilla:
- On occasion, a Doppler can be necessary to locate the pulse
- Insert needle through the skin overlying the pulse
- Aim first anterior, toward the coracobrachialis muscle if it can be palpated, and elicit a biceps response at 1.2 mA. Decrease current to 0.4 mA (while adjusting needle position to maintain the response) and inject 5–7 mL of local anesthetic
- Pull needle back to skin and locate two out of three of the nerves that are located in the sheath around the artery (see responses below):
- Typically, the median nerve is anterior to the artery (toward the ceiling when patient supine)
- Ulnar and radial nerves are posterior to the artery (toward the floor with the patient supine), with the radial being deeper
- However, anatomic variations are common. Often, one has to insert the needle, and if no response is elicited, ...
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