Axillary Nerve Block for Regional Anesthesia
Axillary Blocks Can Be Used for Certain Surgeries
I'm your anesthesia doctor and I'm going to put a needle in your armpit to inject medicine to numb your arm before your surgery.
Luckily, we anesthesiologists don't phrase our procedures so bluntly, but this is the essence of the axillary block. A bit of explanation will help explain why, despite the unpleasant sounding description, this is actually quite a useful procedure under the right circumstances.
Why Use an Axillary Block?
The majority of surgeries are done under general anesthesia, whereby loss of consciousness anesthetizes the brain and whole body. But, sometimes for various reasons, general anesthesia may not be a safe choice, or the best choice. The anesthesiologist, in addition to general anesthesia, has a selection of other anesthetic techniques that may be employed when appropriate.
Regional anesthesia involves using numbing medicine, by injection, to cause anesthesia or loss of sensation to a region of the body. Epidurals, spinals and nerve blocks are included in this category. Various nerve blocks are designed to target specific parts of the body.
Axillary Block is a Peripheral Nerve Block
Peripheral nerve blocks take advantage of the knowledge of which nerves provide sensation to various body parts.
The bundle of nerves supplying the arm are accessible at various spots in the neck and under the arm. Axillary blocks target the nerves that give sensation to the lower part of the arm, the forearm. The under arm location is the best spot to numb these nerves.
Axillary blocks, sometimes supplemented with other nerve blocks or local anesthesia, can be used for surgery between the elbow and the hand. Usually, the axillary block will not numb the nerve that supplies the thumb side of the forearm. This is because this nerve, the musculocutaneous nerve, separates a little before the spot that can be reached by the block. Another injection is placed nearby to get this nerve numb, too.
Notes from the Operating Room
A patient with a history of renal failure on dialysis 3 days per week presents for AV (arterio-venous) fistula placement for future dialysis. She is obese and has a history of sleep apnea, diabetes, high blood pressure and congestive heart failure since a heart attack 4 years ago, and is a former heavy smoker.
General anesthesia is considered a very risky undertaking in this patient with multiple serious medical problems. But, she needs permanent access to her bloodstream for dialysis since the special port placed in her chest can only be used for a limited time before it must be removed.
Instead, in this case, the patient is offered (or recommended) an axillary block for her AV fistula placement which will be located on her left forearm. The block is placed and her arm becomes numb for the surgery. In addition, she receives moderate sedation with very, very careful monitoring of her vital signs. Her operation is completed and she is awake and talking in the recovery room without complication.
Limitations and Risks of the Axillary Block
- Without going into the detailed anatomy of the nerves that supply the arm and hand, it is important to know that the axillary block doesn't cover the whole arm (as described above). Supplemental injections or an alternate technique are often necessary.
- As with other nerve blocks, the time that an axillary block can provide dense enough anesthesia for surgery to be performed is limited.
- Also, if a tourniquet is to be used on the upper arm, the pressure from the tourniquet may still make it difficult to get a patient comfortable. Sedation helps a lot in this circumstance.
- Any time a needle pierces the skin, there is a risk of bleeding or infection. These appear to be relatively low for this procedure.
- All medications have side effects. There are very few side effects from local anesthetics used in a nerve block in the axilla (underarm).
- Complications can occur from the local numbing anesthetic medicine if it is injected into, or leaks into, the bloodstream. The axillary artery is very close to the location of the injection, so the block should only be done by professionals who are familiar with the anatomy of the region. These complications can range from numbness of the tongue, ringing in the ears and sedation all the way to seizures, cardiac arrest and death in severe cases.