Overview of Interscalene Block
The brachial plexus is a group of nerves that supplies the upper arm. It is created from the fifth to first nerves in your spine and travels through muscles in your neck before wrapping around an artery in your armpit. There’s a space between two of these muscles, called the interscalene groove, that can be felt behind the lateral head of the sternocleidomastoid muscle (the long muscle running down the side of your neck that helps you turn your head).
This space is important because doctors can visualize it using an ultrasound, and it is where they can inject a long-lasting local painkiller to block nerve impulses. This can cause numbness and weakness in the upper arm.
An interscalene block is generally done by an anesthesiologist to numb your brachial plexus, or upper arm nerves, prior to surgery. The procedure is typically done in a surgical prep area while you are mildly sedated. It is often used for surgeries involving the collarbone, shoulder, or upper arm. During the procedure, doctors use clean, sterile techniques to identify the interscalene space. They may use a nerve stimulator to ensure they have the right area; the machine causes muscles in the shoulder, arm, or forearm to contract when the nerve is hit. Then they inject a local anesthetic into the space to numb the nerves. This can cause pain relief and a heavy feeling in the limb as the anesthetic starts to work.
As with all procedures, there can be side effects to an interscalene block. For example, if the needle is placed incorrectly it could potentially puncture the lung, damage a nerve, or cause other issues. Using ultrasound can help to minimize this risk. People with lung problems might experience shortness of breath after the procedure due to blockage of the phrenic nerve, which runs in front of the brachial plexus. In addition, the drug used can sometimes spread and affect other nerves in the neck, causing conditions like Horner syndrome, which includes symptoms like drooping eyelids, pupil constriction, and inability to sweat.
During the block placement, doctors also monitor for signs of local anesthetic toxicity. It’s rare, but some people can have allergic reactions to the anesthetic used. Both the patient and the doctor need to know the maximum safe dose of the anesthetic. It’s important to know that allergic reactions to one type of anesthetics are not common but they can occur if the patient is allergic to para-aminobenzoic acid, an ingredient in another type of anesthetic.
Anatomy and Physiology of Interscalene Block
The brachial plexus is a group of nerves which are formed by the joining of the front strands from the lower four neck spinal nerves and one upper chest spinal nerve (these are specifically named C5, C6, C7, C8, and T1). This grouping of nerves continues to form structures known as roots, trunks, divisions, cords, and branches in your body.
These five roots form into three trunks (named superior, middle, and inferior) and these can be found between the front and middle scalene muscles – these muscles are located on the side of your neck. Each of these trunks divides into two parts (called anterior and posterior) behind the clavicle, or collarbone, in your shoulder area. This process forms a total of six divisions.
These six divisions then come together to form three cords (known as lateral, median, and posterior). These cords then create five main or terminal nerve branches, which are known as the musculocutaneous, axillary, radial, median, and ulnar nerves.
Why do People Need Interscalene Block
This procedure is typically done on patients who are having surgery on their shoulder, upper arm, or elbow. However, it’s not advised for those undergoing hand surgery because the lower part of the nerve network in the arm might not be sufficiently numbed.
When a Person Should Avoid Interscalene Block
Some patients should not have this type of nerve blockage treatment. This includes those who have problems with their respiratory system, meaning they may struggle with breathing. This is because the treatment might accidentally block the workings of the phrenic nerve – a nerve that sends signals to your diaphragm, a major muscle involved in breathing. This blockage could impair one side of the diaphragm (a condition called hemiparesis) and may decrease lung function by about 25%.
Moreover, this treatment might also block the recurrent laryngeal nerve. This is a nerve in your throat that controls your vocal cords. So if there’s an already existing issue with this nerve (vocal cord palsy), it could completely block the patient’s airway, making it nearly impossible for them to breathe.
Equipment used for Interscalene Block
For the medical procedure called a block, your healthcare provider will need several items. Here’s what each one does:
* Skin prep such as chlorhexidine, betadine, or alcohol is used to clean the skin to prevent infection.
* A two-inch, 22-gauge, short-beveled, insulated, stimulating needle is used to perform the block.
* A tiny 3-mL syringe plus a 25-gauge needle is used with a local anesthetic to numb the skin.
* A larger 20- to 30-mL syringe is filled with local anesthetic to numb the area of the block.
* A marking pen is used to mark where to perform the procedure.
* Sterile gloves help maintain a clean environment to prevent infections.
* A peripheral nerve stimulator sends mild electrical signals to help the health professional locate the nerves.
* An ultrasound machine provides real-time images of the body’s interior, assisting the healthcare professional in accurately placing the needle.
Who is needed to perform Interscalene Block?
The process of blocking the interscalene, a group of nerves in the neck, involves two medical professionals. One of them uses an ultrasound device to guide a needle to the right place in your body. The other person manages a special machine called a nerve stimulator and a syringe filled with a numbing medicine. This process helps in managing pain and discomfort during certain procedures.
Preparing for Interscalene Block
The patient may be placed in several positions such as lying flat on their back, sitting up, semi-sitting up, or lying on their side. The most common position involves the patient sitting at a 30-degree angle. A pillow or blanket is often placed under the patient’s chest while they are turned away from the side where the procedure will be performed. Here are some important points on how the patient should be positioned:
- The patient should be comfortable and able to remain still in the chosen position.
- The neck area should be clearly visible and easy to reach.
- Necessary space should be available between the patient and the bed. This is important for the ultrasound device and needle, especially if a procedure involving a posterolateral angle (a technique where a needle is inserted from the side and slightly towards the back of the area) is to be done.
How is Interscalene Block performed
Here are two methods that doctors use to perform nerve blocks: using ultrasound guidance or without it. A nerve block is when a doctor injects a numbing medication around certain nerves to help reduce pain or discomfort.
Using Ultrasound for a Nerve Block
In this technique, the patient is comfortably positioned, and the skin area is cleaned for the procedure. A tool that works like a mini-TV called a transducer is placed over the neck area. The job of the transducer is to show a real-time image of what’s happening underneath the skin. Two typical ways are used to get the right image.
The first way involves positioning the transducer at a certain level on your neck, next to a muscle called sternocleidomastoid, around the area of a structure called the cricoid cartilage. Then, they try to identify a blood vessel called the carotid artery. After that, they move the transducer sideways until they see a group of nerves called the brachial plexus located between two muscles (the anterior and middle scalene muscles).
In the second method, they place the transducer a little bit above your collarbone (clavicle) and try to identify both the subclavian artery and the brachial plexus. Then, they move the transducer upward (towards your neck) while keeping the brachial plexus nerves viewable on the monitor until they see the “stop-light” image. After that, they insert the needle in the direction parallel to the transducer.
When the needle reaches the interscalene groove (the gap between the two muscles mentioned above), and after they make sure that they didn’t hit any blood vessels (by a simple maneuver called aspiration), they inject the numbing medicine. If a nerve stimulator is used, this causes your shoulder and arm to move slightly.
Performing Nerve Block Without Ultrasound
In this technique, before they clean your skin, they identify and mark the correct landmarks using a marking pen. These landmarks include your clavicle (collarbone) and the clavicular head of the sternocleidomastoid muscle and the external jugular vein, which is a big vein in your neck that you can see just under the skin. Another useful landmark is the cricoid cartilage mentioned before.
After these landmarks are marked, the skin is prepped – this usually means it’s cleaned and disinfected – and the doctor can feel the anterior and middle scalene muscles with clean, sterile gloves. These muscles are typically located just behind the sternocleidomastoid muscle, close to the level of the cricoid cartilage. The external jugular vein typically crosses the area between these two muscles (interscalene groove).
With the skin appropriately numbed using local anesthesia, they insert the needle just a bit behind the external jugular vein approximately 3 to 4 cm above the collarbone (clavicle) and advance the needle at an angle perpendicular to your skin.
If they use a nerve stimulator, it is connected and the needle is advanced until they see a sign that the stimulator has reached the brachial plexus nerve group. This usually happens when the needle is about 1 to 2 cm deep under the skin. After confirming that the needle tip is correctly placed, the numbing medicine is injected very carefully to avoid injecting into blood vessels.
Possible Complications of Interscalene Block
Getting an interscalene nerve block treatment, which is an injection to block pain in your shoulder or upper arm, has several possible complications to know about. These include:
1. Infection – This means germs could potentially enter your body and cause illness at the injection site.
2. Bleeding or Hematoma – This refers to either regular bleeding or a collection of blood outside the blood vessels in your body.
3. Puncture of a vascular structure – This could occur if a blood vessel gets accidentally punctured during the nerve block injection.
4. Epidural or subarachnoid injection – These are injections in the outer layers of the spine which might happen accidentally while trying to perform the nerve block.
5. Local anesthetic toxicity – This happens when too much anesthesia accumulates in your body causing unwanted side effects.
6. Permanent nerve injury – This is a rare but serious risk, where the nerve being blocked could be accidentally injured, possibly causing long-term damage.
7. Total spinal anesthesia – If the anesthetic is accidentally injected into the wrong area, it could cause a temporary loss of all feeling and movement in your body.
8. Horner Syndrome – A group of symptoms such as drooping eyelid, smaller pupil in one eye, or loss of sweating on one side of the face.
9. Hemiparalysis of the diaphragm – This could happen if the injection affects the nerves controlling your breathing, partially paralyzing the muscle that separates your chest from your abdomen.
10. Pneumothorax – This is a collapsed lung. It is also rare but could happen if an injection in the neck accidentally punctured the lung.
What Else Should I Know About Interscalene Block?
The interscalene block is a type of anesthesia that can numb about two-thirds of the collarbone, shoulder, and the upper part of the upper arm bone. However, it’s crucial to remember that it may not fully numb the lower part of the arm and the forearm, specifically the area served by the ulnar nerve. This is because the cluster of nerves that serve these areas (referred to medically as the C8-T1 trunk) is often not entirely numbed by this type of anesthesia. Additional numbing of the ulnar nerve area may be needed.
Traditionally, the interscalene block hasn’t been completely reliable for hand operations. This type of nerve block is typically used by itself or together with other types of anesthesia to control pain during surgery or the recovery period afterwards.
