Overview of Ultrasound-Guided Serratus Anterior Blocks
Rib fractures or broken ribs, are common injuries that can often occur in individuals admitted to the emergency unit. It’s believed that between 9% to 38% of trauma patients experience this kind of injury. Broken ribs can cause significant health issues and could even be life-threatening, especially in older adults. These fractures can affect the way you breathe, which could lead to serious lung issues like collapsed lung (atelectasis), low oxygen levels (hypoxia), pneumonia, and in severe cases, even respiratory failure.
Pain relief is key when it comes to managing broken ribs, as it not only helps with the discomfort but also impacts the long-term health outcome. Traditionally, strong pain killers like opioids have been used for this, but they can have negative side effects such as slowing down your breathing, affecting your ability to cough and in older adults, causing confusion (delirium).
Because managing pain is such an important part of treating rib fractures, doctors have been looking at using nerve blocks as potentially safer alternatives for pain relief. Nerve blocks are remarkably effective at blocking the pain from broken ribs. However, if a patient has several broken ribs, applying a separate nerve block to each one may not be practical. While using ultrasound to guide the procedure reduces the risk of accidentally causing a lung collapse (pneumothorax), this is still a potential high-risk complication, especially for less experienced doctors. Using nerve blocks can also increase the risk of local and general toxicity due to the amount of anesthesia needed and how quickly it can be absorbed into the body.
Other regional anesthesia techniques to block pain in the chest (thoracic neuroblockade) include the thoracic paravertebral block (TPVB) and the erector spinae block (ESB). TPVB involves injecting a local anesthetic into a space near the spine which can spread to block the spinal nerves. Performing a TPVB provides effective pain relief, but it needs a high level of expertise to perform. It can also cause potential side effects such as low blood pressure (hypotension), trouble urinating (urinary retention), breathing issues, and nausea and vomiting. The ESB involves using ultrasound guidance to identify a layer between the erector spinae muscle and a protrusion on the vertebra (vertebral transverse process), where local anesthetic is then injected. Multiple studies have shown that both TPVB and ESB are effective for providing relief from pain due to acute rib fractures. However, ESB appears to cause fewer side effects. Like the TPVB, ESB also requires advanced procedural skills and a clear understanding of the relevant anatomy.
Finally, an alternate pain-relief method for acute pain in the front and side ribs is the serratus anterior plane block (SAPB). This technique has gained popularity due to its effectiveness, ease of execution, and limited side effects.
Anatomy and Physiology of Ultrasound-Guided Serratus Anterior Blocks
The serratus anterior muscle is a muscle in your chest that starts from the upper edge of your first to the eighth or ninth ribs and attaches to the inner edge of your shoulder bone. This muscle has 7 to 10 tendon-like parts that start from each rib. It is controlled by a nerve known as the long thoracic nerve.
This muscle is surrounded by two possible layers at the level of the fifth rib on the side of your chest: a superficial layer, that is created between the anterior (front) part of the serratus anterior and the posterior (back) part of the overlying latissimus dorsi muscle, and a deep layer, that is created between the posterior part of the serratus anterior muscle and the external intercostal muscles and ribs. Studies have shown both superficial and deep layer injections to be very effective in providing pain control to the front and side of the chest wall and cause loss of skin sensation over a similar area. However, the superficial layer may maintain the numbing effect for a longer time.
The serratus anterior plane block (SAPB) targets the side nerve branches of the thoracic intercostal nerves which come from the front branches of the thoracic spinal nerves and are bundled together right below each rib. These nerve branches go through the muscles and tissues and provide sensation to the side muscles of the chest. Therefore, they travel through the previously mentioned two possible layers. Anesthetics inserted into these layers will spread throughout the side of the chest wall, causing numbness from the second through the ninth sensory skin areas of the front and side of the chest.
Why do People Need Ultrasound-Guided Serratus Anterior Blocks
The Serratus Anterior Plane Block (SAPB) is a technique used to control pain in various situations. It has proven effective in managing pain related to fractures in the front and side areas of the rib cage, rib bruises, thoracoscopic surgery (a procedure involving small incisions in the chest), thoracotomy (surgery where the chest is opened), breast surgeries and pain after a mastectomy (removal of a breast).
It is particularly useful for managing pain from fractures that affect the ribs on the front and side; however, it may not be as effective for fractures on the anterior (front) and posterior (back) of the ribs.
This pain management technique is an option for trauma patients who have more than two rib fractures and need opioid (a type of pain reliever) medicinals to help them breathe comfortably and reduce discomfort.
When a Person Should Avoid Ultrasound-Guided Serratus Anterior Blocks
There are some reasons why a person may not be able to have a SAPB (a type of anesthesia). These can include:
If a person is allergic to the medications used to numb the body (local anesthetics), they can’t have SAPB. It’s also not safe to do SAPB if there’s an infection in the place where the anesthetic needs to be injected.
Certain things can make it harder to see where to place the injection under a sonogram (a kind of imaging test), like scars or tough tissue (fibrosis) from earlier chest surgeries, or air trapped under the skin from an injury. These don’t always mean you can’t have SAPB, but they might make it more risky.
Finally, something called ‘therapeutic anticoagulation’, which is when a person takes medication to prevent blood clots, usually doesn’t stop a person from having SAPB. This is because the injection is given near the skin’s surface and there’s a low risk of injuring a blood vessel, particularly for doctors who have a lot of experience with this procedure.
Equipment used for Ultrasound-Guided Serratus Anterior Blocks
To clearly see and track superficial structures during this procedure, a high-frequency linear transducer is used. This high-frequency device is similar to an ultrasound machine and it operates at a frequency between 5 and 13 million cycles per second (MHz). It can provide detailed images and is ideal for this operation. Generally, a transducer with a larger footprint is preferred as it enables better in-line monitoring of the needle’s length during the procedure.
This procedure involves a relatively large volume plane block. This might sound a bit medical, but simply put, it means that a large area is numbed for the surgery. Therefore, it’s necessary for the patient to have an intravenous line, commonly known as an “IV,” established. This line lets the healthcare team give medication and fluids directly into the patient’s bloodstream.
Additionally, the patient is placed on cardiac monitoring, which would involve wearing sensors on the chest to keep track of heart’s activity. Why is this needed? This is to watch out for a condition known as LAST or Local Anesthetic Systemic Toxicity – a fancy term referring to the toxic effects of the local anaesthetic spreading to the rest of the body which doesn’t happen commonly but is serious when it does.
If LAST does occur, the medical team can quickly treat it using a lipid emulsion therapy, which is a type of treatment that uses fats in liquid form to counteract the toxicity. Having an IV line and cardiac monitoring helps the team to identify and react promptly, if this rare side-effect of the local anaesthetic happens.
Who is needed to perform Ultrasound-Guided Serratus Anterior Blocks?
The SAPB, which is a type of injection, is carried out by trained experts who know how to use special imaging technology related to muscles and procedures. Even though one provider might be enough to do this task, it is usually suggested that two people get involved because the injection involves a good amount of fluid.
The first person uses an ultrasound machine to guide the needle to the right spot while the second person controls the injection’s speed and amount. If there are two people doing the job, they usually connect the needle to a tube which is then connected to a special device called a three-way stopcock. This device has one port connected to a saline solution (to clean or rinse) and another port connected to the medicine syringe (the medicine-filled part of the injection).
Preparing for Ultrasound-Guided Serratus Anterior Blocks
Before starting the procedure, the doctor needs to get the patient’s consent, meaning that they understand and agree to what will happen. The doctor will use a special machine called an ultrasound, which helps them look inside your body. This machine needs to be in line with the doctor’s view and the needle for the best accuracy. To keep everything clean and prevent infections, they’ll use clean equipment, including a protective cover for the ultrasound tool and clean gel.
The patient can lay down flat on their back or on their side during the procedure, depending on what feels more comfortable. It’s important to make sure the area of the chest where the doctor will use the needle is clean. A common cleansing solution contains 2% chlorhexidine, although other similar products might be used depending on the hospital’s guidelines.
How is Ultrasound-Guided Serratus Anterior Blocks performed
For this type of scan, you need to place a special device, known as a high-frequency linear transducer, on the side of your chest, about halfway between the front and back, at the level of the fifth rib. The image depth should be set so that we can see your rib, the line going around your lung (pleural line), and the muscles on top of your ribs (the serratus anterior and latissimus dorsi muscles). This usually requires a depth of 3-5 cm, but this can vary depending on the patient’s body size.
Before the procedure begins, a small amount of local anesthetic can be given to numb the skin where the needle will enter. Then, with the help of the ultrasound, the needle is carefully directed towards the fifth rib at about a 45-degree angle. Depending on the type of chest block, the local anesthetic is injected in different spots.
In the superficial chest block, the anesthetic is injected into the space created with the muscle on your back; that space is just in front of the serratus anterior muscle. There is a blood vessel there called the thoracodorsal artery. Your doctor will take special care not to puncture it, and if you see the anesthetic spreading around the vessel, it means that it’s being injected in the right place.
In the deep chest block, the anesthetic is injected in front of the rib and beneath the serratus anterior muscle.
Throughout the procedure, the needle can be seen on the ultrasound to ensure it doesn’t touch any blood vessels while it’s passing through the soft tissues. Once the needle is in the right place, a small amount of liquid, either normal saline or anesthetic, is injected to confirm the needle’s position and to prepare the space where the anesthetic will be injected.
After making sure everything is in the right place, a larger volume of a diluted anesthetic, like bupivacaine, is slowly injected. This will look like a growing dark line between the layers of tissue on the ultrasound image. After the injection, the needle is removed, and the area where it entered your skin is covered with a special bandage.
Possible Complications of Ultrasound-Guided Serratus Anterior Blocks
After getting an operation, some patients could experience what’s called “rebound pain”. This is because the pain relief provided by a drug known as bupivacaine usually lasts about six hours. One possible side effect of regional anesthesia (a type of pain blocker used for certain parts of the body) is a condition called Local Anesthetic Systemic Toxicity (LAST). To reduce the chance of this happening, doctors use a weaker form of the anesthetic and stick to a maximum dose of 2 mg per kg of patient body weight.
A pneumothorax, or collapsed lung, could potentially occur but that would usually indicate a serious mistake by the medical provider. This is because the area targeted for the operation is right above the ribs, and the lung can be clearly seen on an ultrasound scan. If a collapsed lung is suspected, an ultrasound can help check if the lung is moving normally straight after the procedure.
Injury to the nerves is unlikely as the doctor is careful to guide the needle towards the areas around the nerves instead of directly at them.
What Else Should I Know About Ultrasound-Guided Serratus Anterior Blocks?
Using ultrasound guidance, a Serratus Anterior Plane Block (SAPB) is an effective method for managing pain on the front and side of your chest. It’s especially beneficial when dealing with broken ribs due to an injury. This approach is a good option compared to using strong painkillers, which can have a high risk of side effects, especially for older people.
