Overview of Axillary Block
The way to numb the brachial plexus nerves using the underarm or ‘axillary’ approach was first explained by Dr. Halstead and his team in 1884. This method was particularly helpful before the widespread use of ultrasound because of its safe position close to the skin’s surface and low risk of problems like collapsed lungs (pneumothorax). This made it a practical choice for minor outdoor hand surgeries.
Due to its easily accessible location, it’s simpler for doctors to locate the individual nerve branches using a nerve stimulator or ultrasound techniques. It’s important to note that despite its name, this method doesn’t numb the axillary nerve. So, it shouldn’t be mixed up with the somewhat new method that blocks the axillary nerve.
The rest of this information will only focus on the underarm approach to numbing the brachial plexus nerves.
Anatomy and Physiology of Axillary Block
The brachial plexus is a bundle of nerves that sends signals from your spine to your arm, hand, and shoulder. It starts from the neck area and extends down to the shoulder, providing sensation and movement to the hand and arm.
This nerve bundle weaves its way between two muscles in the neck that help us turn our heads and necks. At this point, it forms three “trunks” or paths, each made up of different nerves. The first two — the C5 and C6 nerves — pair up to form the top trunk, branching off to form another nerve known as the suprascapular nerve. The C7 nerve forms the middle trunk, while the last group, the C8 and T1, form the lower trunk.
Each nerve trunk then splits again behind a major artery (the subclavian artery) in the upper chest. These splits regroup around the axillary artery, which is found near the shoulder joint and armpit. Here, they form the three ‘cords’ of the nerve bundle. The cord names represent their location in relation to the axillary artery.
Near the chest, the brachial plexus breaks up into smaller nerves that connect to the muscles in the arm and provide feeling to different parts of the arm and hand. The musculocutaneous nerve is one such nerve, branching from the lateral cord. From the medial cord, we get the ulnar nerve, which gives us feeling in part of the hand. Other nerves like the axillary and radial nerves come from a cord at the back.
Looking at the axilla, or armpit, it guards an important space beneath the shoulder joint, bordered by your collarbone (clavicle), upper shoulder bone (the scapula), various torso muscles, and your upper arm bone (the humerus). An important landmark to understand is the axillary artery pulse, located below a chest muscle (pectoralis major). Above this spot, we can pinpoint where the musculocutaneous nerve block is.
When using ultrasound to view this area, the axillary artery and the surrounding nerves can be clearly seen. The placement of the nerves slightly changes individually, but in general: the median nerve is found to the side and above the axillary artery, the ulnar nerve is found medial and above the artery, and the radial nerve is behind the artery. The musculocutaneous nerve may be found within the connective tissue between the biceps and a nearby muscle (coracobrachialis), which is near the armpit, collarbone, and upper arm.
Why do People Need Axillary Block
This method effectively numbs the elbow, forearm, and hand for medical procedures. But without an extra step to block the musculocutaneous nerve (a nerve in your arm), there may not be enough numbness in the forearm. This might leave the front and outer parts of your forearm able to feel pain.
This method wouldn’t work well for procedures specifically in the armpit area (axillary).
When a Person Should Avoid Axillary Block
Sometimes, certain conditions can prevent a person from having a specific type of anesthetic block (a method to numb a particular area). For example, if an infection is present at the underarm injection area, or if the patient doesn’t want the procedure, these are solid reasons not to use this block.
Other conditions might advise against using the block, but it can still be done with caution. These include pre-existing nerve damage causing feelings like numbness, tingling or muscle weakness. The presence of these symptoms should be examined and recorded before the procedure, since they might mean a higher risk of further nerve damage. Also, having a blood thinning treatment (anticoagulation) or severe lung disease could also advise against the block. These factors might make it more risky, but not impossible.
Equipment used for Axillary Block
Here are the items that a doctor needs when performing a nerve block (a procedure to numb a certain part of the body):
– Sterile gloves, to keep everything clean
– A standard nerve block tray which includes chlorhexidine prep, a small syringe filled with a local anesthetic called lidocaine, and a thin needle.
– A local anesthetic (either ropivacaine or bupivacaine) in a larger 20-25 ml syringe. This is a medication to numb an area of the body.
– A 5-cm, 20-gauge short-bevel insulated needle, that might be stimulating or non-stimulating. A needle is an instrument used to inject the local anesthesia into the body.
– An ultrasound machine with a linear transducer, sterile sleeve, and ultrasound gel. This is used to guide the procedure, the sleeve keeps the machine sterile and the gel helps conduct the sound waves. Ultrasound is a special kind of imaging that uses sound waves to create pictures of the inside of your body.
Who is needed to perform Axillary Block?
Apart from the healthcare professional who does the nerve block task, which is a technique used to decrease pain in a certain area of your body, another person is required to deliver the local anesthetic. A local anesthetic is a medication that numbs a specific part of your body to block any discomfort during the procedure.
Preparing for Axillary Block
Before having a nerve block procedure, it’s very important for the patient to understand what it involves, which is known as giving ‘informed consent’. This is to make sure the patient is fully aware and agrees to what is about to happen.
During procedures like nerve block, certain standard monitors are used to check the patient’s vital signs. These include constant heart monitoring (electrocardiography), a machine to check oxygen levels in the blood (pulse oximetry), and blood pressure checking. It’s also necessary that the patient has a ready intravenous (IV) line setup to quickly administer fluids or medications if required.
Also, emergency life-support equipment and medications need to be readily available in case of any unexpected event. This includes, oxygen source, resuscitation bag (a device used to assist with breathing), airway devices, certain specific medicines such as vasopressors (to increase blood pressure) and 20% lipid emulsion (fat particles in a water-based solution that can help manage certain medication toxicities).
During nerve blocks utilizing ultrasound, the patient will need to position their arm in a way that provides the best access to the area being treated. To do this, the arm should be moved away from the body at least at a 90 degrees angle. The forearm can then be rested comfortably, either leveled at 90 degrees or above the head or behind the head. It may seem odd, but it helps the doctor see better where the medication needs to be placed.
How is Axillary Block performed
In simple terms, some research suggests that using ultrasound to guide the process of a nerve block in your armpit (axillary area) is quicker, more successful, and comes with fewer complications than other methods. It also usually needs less local anesthetic (numbing drugs), so in this write-up, we will describe how it’s done.
Imagine that the doctor is standing ‘uphill’ in relation to your outstretched arm. They feel for a specific point in your armpit where a big muscle (pectoralis major) attaches. Just below this muscle, they place an ultrasound device to get a clear picture of the axillary blood vessels and nerves in your arm.
The axillary vein, a large blood vessel, is seen on the ultrasound screen towards the inner side of the artery. It’s important not to press too hard with the ultrasound device, as this could squash the vein and hide it from view. If the vein isn’t visible when the nerve block is carried out, there’s a risk of accidentally puncturing it, or injecting the anesthetic into it.
At the hospital where this procedure was observed, the doctors prefer to insert the needle from above to below. Before inserting it, they numb your skin with a small shot of lidocaine to keep you comfortable. The radial, median, and ulnar nerves are then targeted around the axillary artery, the main blood vessel. These nerves aren’t too deep, usually 1 or 2 centimeters below the skin. It’s important that the needle gets close to these nerves for the nerve block to be effective.
The musculocutaneous nerve is found in the layer between two muscles in your upper arm (biceps brachii and coracobrachialis muscles), or within the coracobrachialis muscle itself. The doctor might keep the needle at the same entry point and just change its direction to block this nerve. If it isn’t blocked, you may still feel some sensation in the front and side of your forearm.
During the procedure, the doctor takes certain precautions to keep you safe. They give the anesthetic in separate doses and withdraw some fluid from the area before each injection to make sure they’re not in a blood vessel. They avoid injecting if the pressure is high, or if you report “pins and needles.” If these sensations occur, they will reposition the needle until they subside.
Possible Complications of Axillary Block
There are a few complications that can possibly occur after surgery, but they’re quite rare. They include:
– Infection: this could happen at the site of the surgery.
– Bleeding or formation of a hematoma: a hematoma is a collection of blood outside of the blood vessels, often looking like a bruise.
– Nerve injuries: these can include neuropraxia (a mild nerve injury), axonotmesis (a more serious nerve injury), and neurotmesis (the most severe type of nerve injury).
– Accidental injection into a blood vessel: this could occur while giving medication or anesthesia.
– Local anesthetic systemic toxicity: this happens when too much of a local anesthetic gets into the bloodstream. This could cause symptoms such as metallic taste, numbness, or in more severe cases, seizures or heart problems.
What Else Should I Know About Axillary Block?
Using the axillary approach for certain medical procedures may have less chance of causing phrenic nerve palsy, a condition that can cause difficulty in breathing, because it’s further away from the phrenic nerve. This phrenic nerve controls the diaphragm, a major muscle that helps you breathe. The proximity can lead to more issues with other methods such as the interscalene and subclavian approaches.
If you have serious lung disease or weakness on the opposite side of your diaphragm, the axillary approach could be the better choice for you. Remember, your medical provider will consider all these factors and your specific health condition to determine the best approach for you.
