Acute Chest Syndrome

Acute Chest Syndrome

Sickle cell disease (SCD) or anemia is an inherited blood disorder that affects the hemoglobin in the red blood cells. Acute chest syndrome (ACS) is a severe lung-related complication of sickle cell disease that affects both children and adults. It creates a pneumonia like illness and is one of the leading causes of morbidity, hospitalizations and death in children and adults living with sickle cell disease. ACS occurs when sickle red blood cells block blood vessels in the lungs. This is considered an emergency and may be life threatening.

How Acute Chest Syndrome Affects Your Body

Hemoglobin is the protein in red blood cells that carries oxygen in your body. A person with sickle cell anemia makes a different type of hemoglobin called sickle hemoglobin. While normal red blood cells are shaped round, flexible and smooth, red blood cells that contain sickle hemoglobin develop an irregular shape like a crescent or banana.
Acute chest syndrome happens when these sickle cells block the small blood vessels in the lungs. This blockage reduces blood flow and the amount of oxygen that travels out to nourish the body. The longer the small blood vessels are blocked, the more damage can be done to other organs of your body.

Key Facts:

• Acute chest syndrome can be life-threatening and accounts for close to 25% of deaths in adults with sickle cell disease (SCD).
• The peak incidence of ACS in children is ages 2 to 4.
• Because it is potentially fatal, it requires immediate intervention regardless of age
• If you are living with asthma and SCD, you are five times more likely to have respiratory symptoms at the time of a Vaso-occlusive crisis (VOC). A VOC occurs when sickled cells block blood flow resulting in tissues being deprived of oxygen.
• With timely treatment, most people can recover. 
• While the cause is unknown, long-term complications of repeated ACS include interstitial lung disease and pulmonary hypertension.

Who Is at Risk?

There is no single cause of ACS, however certain conditions can trigger it. ACS can be brought on suddenly when the body is under stress from illness or dehydration. 

• Other Medical Conditions: Pulmonary embolism (blood clots from other parts of the body travelling to the lungs), pulmonary fat embolism (bone marrow tissue travelling from the bones to the lungs), pulmonary artery thrombosis (blood clots forming in the lungs), infections like pneumonia, and asthma. 
• Coronavirus disease 2019 (COVID-19) has been reported as a cause of ACS
• Vaso-occlusive crisis (VOC): Vaso-occlusive crisis (VOC) which is a common complication of SCD, presents with excruciating pain, usually of sudden onset, although it may be a gradual onset. The pain is often concentrated to the extremities like your arms and legs, chest or back.  ACS may be a complication of VOC.
• Low oxygen levels: Low oxygen in the lungs and blood leads to the formation of sickle cells. This may be the result of infection in the lungs.
• Low Fetal Hemoglobin (HbF): Fetal hemoglobin or HbF is the main form of Hemoglobin in the fetus. HbF continues after birth and being in red blood cells protects against sickling. Low levels of HbF can increase the risk of ACS. 
• Genotype: Sickle Hemoglobin is the product of the sickle gene S. Genes exist in pairs and individuals with SS have the most serious form of SCD. S may be present with another variation of the hemoglobin gene such as C which causes a less severe form of the disease.
• Age: ACS can occur at any age. In children with SCD peak onset of ACS occurs ages 2 to 4 years old. 
• Infection: ACS in children is often triggered by infection
•  Recent trauma or surgery: Due to pain and medications post-surgery, you may experience shallow breathing and low oxygen levels resulting in sickling in the lungs that cause ACS. 
• Smoking or secondhand smoke exposure: Smoking or exposure to secondhand smoke is associated with a higher risk of ACS and more severe episodes in children.

What Are the Symptoms of Acute Chest Syndrome?

The signs and symptoms of acute chest syndrome can vary. Children are more likely to have an infection that will present respiratory symptoms and fever. Adults are more likely to have pain in the chest, arms, and legs, as well as shortness of breath and vaso-occlusive pain episodes. 
The most common symptoms are:

• Shortness of breath
• Wheezing
• Rapid shallow breathing (tachypnea)
• Cough, which may contain blood
• Fever
• Chest or back pain
• Vaso-occlusive pain

How to Diagnose Acute Chest Syndrome?

It is important to get immediate medical treatment if you suspect ACS. If you go to an emergency room or hospital, you should notify them that you have sickle cell disease. During your exam, your physician will conduct a physical exam and ask about your personal history, including any potential risk factors. Diagnosis is based on test results from chest imaging, medical history and symptoms.

Common tests that may be ordered are:

• Chest X-ray of your heart and lungs
• Pulse oximetry to measure oxygen saturation
• Blood tests including complete blood count, metabolic panel, cultures (to rule out infection), type and cross match (due to the potential need for transfusion) 
• Bronchoscopy with BAL to evaluate other sources of infection if symptoms are not improving with supportive care and antibiotics
• A CTA or computed tomographic angiogram is a special type of X-ray that is the most common test used to diagnose pulmonary embolism because it uses contrast to analyze blood vessels. A Ventilation perfusion scan may be ordered instead if you are allergic to the dye used for a CTA.
• D-Dimer (blood test) to screen for possible pulmonary emboli
• Ultrasound of the legs to measure blood flow speed
• Electrocardiogram to record heart activity
• MRI is usually reserved for pregnant women and individuals that may not be able to tolerate the contrast used in other imaging tests 

How Acute Chest Syndrome Is Treated

Treatment must be aggressive since the disease can progress quickly and can be fatal. ACS treatment may include pain control, intravenous (IV) fluids if dehydration is suspected, antibiotics to treat infection, supplemental oxygen, and blood transfusions. 
If you are hospitalized for a vaso-occlusive pain episode, you may be provided with an incentive spirometer. An incentive spirometer is a device that will help you expand your lungs and breathe deeper and fuller. It helps to prevent areas of lung collapse, also known as atelectasis. Atelectasis may increase hypoxia or low oxygen in the blood. Bronchodilators may be used when there is underlying asthma or pulmonary disorders. If oxygen therapy is inadequate to treat low oxygen levels, additional treatments are needed to prevent respiratory failure. These treatments may include noninvasive ventilation like BiPAP. In more serious cases intubation and extra corporeal membrane oxygenation (ECMO) may be required. Treatment for ACS will usually require hospital admission to monitor oxygen levels and clinical status. Treatment with corticosteroids is sometimes used.
A new gene therapy, called LentiGlobin, is being studied for long-term results that may provide a potential cure for sickle cell disease. You can learn more about this hopeful treatment in our Lungcast episode, “The Troubling Cycle of Sickle Cell Disease” with Dr. Ify Osunkwo.

How Can Acute Chest Syndrome Be Prevented

If you have asthma or another lung disease, it is important to follow your lung disease treatment and management plan and follow up with a pulmonary doctor. Lung diseases, like asthma, are related to higher rates of ACS and reduced lung function over time. For example, people living with sickle cell disease and asthma are two to four times more likely to get ACS than people with sickle cell disease alone. 
Your healthcare may prescribe Hydroxyurea, which is a medication that can increase HbF and is used to treat SCD. Hydroxyurea can help reduce the pain, the need for blood transfusions, and prevent episodes of ACS. The length of treatment may vary, and routine blood tests and close monitoring may be needed, as there are side effects to this medication. 
Chronic transfusions may be used during high-risk months for respiratory infections, like winter.  Chronic transfusions are used to support the transition to hydroxyurea or if you are recovering from a life-threatening ACS. Stem cell transplants may be considered if hydroxyurea is not working to prevent recurring ACS episodes. 
You should also stay up to date with vaccinations that protect you against infectious respiratory diseases like COVID-19, flu and pneumonia. There is a risk of long-term complications with recurring ACS episodes. These complications include reduced lung function, interstitial lung disease and pulmonary hypertension. 

For more information:

Some resources available to patients include:

• Sickle Cell Disease Association of America
• Centers for Disease Control

Source: https://www.lung.org/lung-health-diseases/lung-disease-lookup/acute-chest-syndrome