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Axillary Brachial Plexus Block: Technique
Transducer position
- Place the transducer in a transverse orientation over the intersection of the pectoral major and biceps muscle insertion. Do not place the transducer too high in the axillary fossa.
Scanning
- Identify the axillary artery, about 1-3 cm from the skin surface.
- Pre-scan with proximal-distal movements adjusting the ultrasound image to identify the structures of interest:
- The axillary artery (AA)
- The conjoint tendon
- The neurovascular sheath containing the median (MN), ulnar (UN), and radial (RN) nerves.
- The muscles, and the musculocutaneous nerve (McN).
Fig. AA, Axillary artery; AV, Axillary vein; V, vein; McN, Musculocutaneous nerve; MN, Median nerve; UN, Ulnar nerve; RN, Radial nerve; MbCN, Medial brachial cutaneous nerve.
Needle insertion
- Insert the needle in-plane from lateral to medial toward the posterior aspect of the AA:
- Deposit local anesthetic below the AA first (8 mL). This decreases the displacement and re-arrangement of the anatomical structures.
- Next, redirect the needle and inject an additional 8 mL above the AA.
- Finally, perform a separate injection to block the McN (4 mL).
Fig. AA, Axillary artery; AV, Axillary vein; V, vein; McN, Musculocutaneous nerve; MN, Median nerve; UN, Ulnar nerve; RN, Radial nerve; MbCN, Medial brachial cutaneous nerve.
Depending on the disposition of the nerves around the AA, and the spread of the local anesthetic after the initial injection, the block can be accomplished with one to four separate injections.
Alternative needle insertion approach
- Insert the needle in-plane between the AA and the MN, and inject 8 mL of local anesthetic. If there are no veins on the path, further advance the needle to inject another 8 mL of local anesthetic. These injections should spread in a U-shaped fashion around the AA covering the MN, UN, and RN.
- Withdraw the needle to complete the block of the McN separately (4 mL).
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