The Axillary Nerve Block is an intermediate level procedure that will allow you to sharpen your skills as a sonographer since you will be moving your needle around to target three and sometimes four nerve branches (radial, ulnar, median, musculocutaneous). With ultrasound, and with a single point of entry, you will be able to perform this 4:1 block with ease after some practice.
Indications: Upper extremity procedures
External Landmarks: Axilla, axillary crease
Approach: In-Plane our Out-of-Plane
Local Anesthetic Volume: 20 - 30 mls.
Level of Expertise: Intermediate
The brachial plexus enters the axilla as a squadron around the axillary artery, which will be your main landmark. The nerves are usually located in the following way:
Most Lateral: Median
Most Medial: Ulnar
Beneath the Artery: Radial
View of Axillary Anatomy with a non-linear array ultrasound
Place your arm in anatomical position, and you will see it is easy to remember the above anatomy since your ulnar nerve which innervates your 5th finger (and half of the 4th) will be most medial.
You can do this block in and out of plane. Our preference is in plane since we can usually target all the above nerves, plus the musculocutaneous with a single entry point. This will take some practice, but after a while you will be doing this without much difficulty.
Supine, with the patient's arm abducted in the "Marylin Monroe" (or "Brigitte Bardot") position.
- I-Streme Echo
- Nerve stimulator (optional)
- 20-30 mls local anesthetic syringe (use Ropivacaine for further sparing of phrenic nerve)
- 25 gauge needle for local infiltration
- Echogenic needle (optional)
- 10 MHz setting
- Place the probe with its button facing the head and along the axillary crease.
- Locate the axillary artery, and identify the median, ulnar and radial nerves.
- Locate the musculocutaneous nerve, beyond the radial nerve and within the coraco- brachialis muscle.
- A nerve stimulator will help you to confirm the anatomy easily when your needle is moved around.
- Start injecting the median and ulnar nerve with 7-8 mls of local anesthetic.
- Proceed to the radial nerve and then insert your needle deeper so that its tip is adjacent to the musculocutaneous.
- Watch out for veins near the artery since you could inadvertently inject anesthetic into these.
- A doughnut sign around the axillary artery is usually indicative of good local anesthetic spread for this block.
- Intravascular injection into the axillary artery or vein.
- Nerve injury.