Overview of Axillary Block
The method of using an axillary approach for a brachial plexus nerve block was first introduced by Dr. Halstead and his team in 1884. A brachial plexus nerve block is a type of anesthesia used to numb the upper part of your arm for surgery. With the advent of ultrasound technology, using the axillary approach has become popular due to its relatively simpler procedure and lower risk of complications like pneumothorax, which is an abnormal collection of air or gas in the chest that can cause the lung to collapse.
The axillary approach involves administering the anesthesia towards your armpit region. Despite the name, an important thing to remember is that this procedure doesn’t affect the axillary nerve, a nerve in your shoulder. So, it’s different from the more recently introduced axillary nerve block procedure. Their similarity in name might be confusing, but they are distinct techniques.
As this procedure is used frequently for outpatient hand surgeries, being aware of the axillary approach to the brachial plexus can be beneficial. Notably, because of its shallow position under the skin, medical professionals can pinpoint the individual nerve branches more easily using nerve stimulators or ultrasound.
In this piece, our focus will be solely on the axillary approach to the brachial plexus.
Anatomy and Physiology of Axillary Block
The brachial plexus is like a large junction box of nerves that start from the lower neck and upper chest and go all the way to the hand. These nerves carry signals between the brain and the arm. The plexus, or network, is formed by five main nerves, called C5, C6, C7, C8, and T1. There are also small contributions from the C4 and T2 nerves.
These nerve roots run between two layers of tissue that cover the front of the vertebrae. They pass through two muscles in your neck, where they join together to form three main “trunks”. The C5 and C6 nerves form the top trunk, the C7 forms the middle trunk, and the C8 and T1 form the lower trunk.
Each of these trunks then split into two “divisions” behind the subclavian artery, which is in your shoulder area. The divisions then regroup around the axillary artery, which is an extension of the subclavian artery, to form three “cords”. Each cord is named based on its position relative to the axillary artery.
These cords then send off branches of nerves at the side of the pectoralis minor muscle, which is a muscle in your chest, to supply different parts of your arm. For example, the musculocutaneous nerve, which comes from the lateral cord, supplies the front of your arm, and the ulnar nerve, which comes from the medial cord, supplies your little finger and half of your ring finger.
The axillary region, under your armpit, can be imagined like a pyramid with a flat top. The top of the pyramid is toward your shoulder, and the bottom is your armpit. The walls of the pyramid are formed by different muscles and bones in your body, such as your pectoral muscles at the front, your scapula (shoulder blade) and few muscles at the back, and your humerus (upper arm bone) and ribs on the sides.
For certain procedures, the doctors might use the pulse of the axillary artery, which can be felt just underneath the pectoral muscles, to find the nerves. Also, with the help of an ultrasound scan, the nerves and the artery in your armpit area can be clearly visualized.
The position of the nerves can vary from person to person; however, usually, the median nerve is found just outside and above the axillary artery, the ulnar nerve is found outside and below the artery, and the radial nerve is found at the back of the artery. The musculocutaneous nerve is usually found between the biceps and coracobrachialis muscles, which are two muscles in your arm, or within the coracobrachialis muscle.
Why do People Need Axillary Block
This procedure is usually used for surgeries on the elbow, forearm, and hand. However, if it’s done without an additional block for the musculocutaneous nerve (a nerve in your arm), it might not fully numb the front and outer parts of your forearm.
Also, this procedure isn’t a good fit for surgeries that need to be done in the actual armpit area.
When a Person Should Avoid Axillary Block
There are certain reasons why a person cannot use this treatment, like an infection in the armpit where the injection is supposed to go, or if the patient doesn’t want it. This makes it absolutely impossible to use this method.
Other health issues may also make this treatment more risky and potentially not the best option. If a person has existing damage to their nerves, including symptoms like numbness, a feeling of pins and needles (known as paresthesia), or weakness in moving parts of their body (known as motor weakness), these factors need to be checked and recorded before any treatment. This is because there could be a higher chance of even more damage to the nerves.
Other conditions, like taking medication to thin the blood (known as anticoagulation) and having serious lung disease, might also make this treatment potentially risky and not the best option. These conditions don’t necessarily prevent the treatment, but they do need to be carefully considered.
Equipment used for Axillary Block
For this procedure, the doctor will need the following:
* Sterile gloves, which are special gloves that are completely free of any bacteria or other germs to help prevent infection.
* A standard nerve block tray is used which includes chlorhexidine prep, which is a substance used to clean the skin to prevent infection. The tray also includes a small 3-ml syringe filled with 1% lidocaine, a local anesthetic or numbing agent, administered with a 25-gauge needle.
* Local anesthetic or numbing medication to help you not feel pain during the procedure. The anesthetic will be placed in a syringe and the doctor will use 20-25 ml of either ropivacaine 0.5% or bupivacaine 0.5%. Both of these medications are strong local anesthetics.
* 5-cm, 20-gauge short-bevel insulated needle, which may either be stimulating or non-stimulating. This needle is specially designed to be used in nerve block procedures.
* An ultrasound machine with a linear transducer (8-14 MHz), sterile sleeve, and ultrasound gel. The ultrasound helps the doctor see where to place the needle, the transducer is a type of sensor that helps create the ultrasound image, and the gel helps improve the quality of the ultrasound image.
Who is needed to perform Axillary Block?
When you are getting a nerve block, it isn’t just one person who is involved in the process. Besides the doctor who performs the nerve block (a procedure that helps to numb a specific area), a second person is also required. This person’s job is to inject the local anesthetic, the medicine that helps with numbing the area being treated. This team approach ensures that your treatment is safe and effective.
Preparing for Axillary Block
Before a doctor performs a nerve block procedure, they need to explain what will happen during the procedure and ask for your consent. This is important because it gives you a chance to ask any questions and to agree to the procedure after you have thought about it.
During the nerve block, they’ll be checking on you often. They’ll use a machine to measure your heartbeat, and a small clip on your finger to check your oxygen levels. They’ll also frequently check your blood pressure as well. An intravenous (IV) line will be set up as well, which is a tube that goes in your vein used for giving fluids or medicines.
The team will also make sure they’ve got all the emergency equipment and medicines they might need, just in case anything unexpected happens. This includes an oxygen source, a resuscitation bag to help with breathing, airway devices, along with medication to increase blood pressure if needed and a special fat-based solution called lipid emulsion that can be used if necessary.
For the nerve block, you’ll need to be positioned in a certain way so the doctor can easily access the area they need to. They’ll ask you to move your arm out to the side, at a right angle to your body. Your arm may be comfortably supported, either held straight out or above, or placed behind your head.
How is Axillary Block performed
Research has shown that using ultrasound guidance for an axillary brachial plexus nerve block (a technique to numb the nerves in your arm) can be faster, more successful, and safer. It also requires a smaller dose of the numbing medication (local anesthetic). So, we will provide a brief overview of the ultrasound technique used in this procedure.
To begin, the doctor doing the procedure will use their fingers to feel the spot where a large muscle in your chest (pectoralis major) attaches to your armpit. Slightly beneath (distal to) this muscle, they place an ultrasound device. This device allows the doctor to see inside your arm and identify the axillary vessels (sort of like the highways of your arm for blood flow) and nerves.
The axillary vein, which carries blood back towards your heart, is located towards the middle (medial) from the artery. It’s really important that this vein isn’t squished or “compressed” because it could disappear from sight on the ultrasound, making it hard to see. If the doctor can’t see this vein while they’re doing the nerve block, they might accidentally poke it or inject local anesthetic into it.
At our agency, we prefer a method where the needle is inserted from top to bottom (superior to inferior). Before the main needle is inserted, a small amount of a numbing medicine known as 1% lidocaine is injected into your skin to make the process more comfortable for you. The goal is to aim for the radial, median, and ulnar nerves around the axillary artery which is usually only 1 or 2 centimeters from the skin surface. It is important to note that within our bodies, compartments are created by fibrous divisions called “septa.” The needle has to be placed very close to the nerves for the nerve block to be successful.
Another nerve, called the musculocutaneous nerve, is located between two muscles in your arm (the biceps brachii and coracobrachialis) or within the coracobrachialis muscle. The needle can usually stay in the same spot as before, but it is redirected towards these muscles to numb this nerve. If this nerve is skipped, the front and side of your forearm might not be numbed correctly.
During the whole process, doctors make sure to use safe practices, such as injecting the local anesthetic in small increments, and always checking (aspirating) to make sure they haven’t accidentally entered a blood vessel before injecting the local anesthetic. Also, if a patient reports feeling tingling or “pins and needles” sensation (paresthesia), the doctor will carefully pull the needle back out a bit until the tingling stops, and then adjust the needle’s direction.
Possible Complications of Axillary Block
There’s a small chance that you might experience complications after a medical procedure. These could include:
– Infection: This happens when harmful bacteria enter your body, most often through the wound made during the procedure.
– Bleeding or Hematoma: This is when there is bleeding inside your body that may cause a buildup of blood, also known as a hematoma.
– Nerve Injuries: This can occur if your nerves are accidentally injured during the procedure. There are different types of nerve injuries, including neuropraxia, axonotmesis, and neurotmesis, which vary based on severity and how the nerve is affected.
– Inadvertent Intravascular Injection: This refers to when a medicine or other substance is accidentally injected into a blood vessel instead of the intended area.
– Local Anesthetic Systemic Toxicity: This is a rare but serious complication that can occur if too much local anesthetic – the medicine used to numb a specific area of your body during the procedure – enters your bloodstream.
What Else Should I Know About Axillary Block?
The axillary approach refers to a particular method or direction during a medical procedure. It may be a safer choice because it minimally affects the phrenic nerve, a key nerve in the body that sits near the lungs and heart. In contrast, other techniques such as the interscalene and subclavian approaches are more likely to inadvertently damage this nerve, which can cause issues such as a phrenic nerve palsy (weakness or paralysis of the diaphragm, the muscle that helps with breathing).
So, if you have severe lung disease or if the muscle that helps you breathe on one side of your body is weak or not fully active (a condition known as contralateral hemidiaphragmatic paresis), then your doctor may recommend the axillary approach. The goal is to avoid further complications, thus making this procedure safer for patients with these conditions.