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Ultrasound-guided axillary nerve block

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Through the use of ultrasound it is almost always easily possible to visualize the 4 main nerves and then irrigate them with local anaesthetic. It is not without reason that one can speak in this area of an individual nerve block rather than a plexus block. The axillary artery and the axillary vein, along with the fascia of the triceps arm muscle, serve as anatomic landmarks. Worthy of note is the enormous anatomic variability of nerves and blood vessels in this region.


The Technique

AxillaerThe ultrasound-guided axillary block can be carried out on both the long and short axes. We now recommend access on the long axis. The positioning of the arm is no different from that of the conventional technique, that is, with abduction of the arm at ca. 90° in relation to the shoulder. The probe is set as near the axilla as possible perpendicular to the path of the nerves and vessels. On both sides of the (pulsing) artery the median nerve, lying cranial to it, and the ulnar nerve, lying caudally to it, can be shown relatively well. The radial nerve, dorsal to the artery, sometimes causes difficulties. The musculocutaneus nerve is usually to be found quite a distance away as a characteristic, hyperdense „eye“ in the area of the coracobrachial muscle, but its prominent features make it easy to detect and irrigate. In actual practice, the puncture is carried out in the ultrasound plane from a cranial direction, initially in the direction of the median nerve, which is irrigated with ca. 5 ml of local anaesthetic. This „flushes“ and clears the path to the ulnar nerve, which itself is then treated with another 5 ml of local anaesthetic. Now the needle is retracted a little and repositioned dorsal to the artery in the area of the radial nerve. This often becomes clearer only after application of a further bolus of local anaesthetic. The procedure is completed with the block of the musculocutaneus nerve. A total of 20 ml of local anaesthetic should suffice to block the 4 individual nerves.

 

Sonoanatomic Landmarks

Axillary artery and axillary vein, latissimus dorsi muscle

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