Pulmonary Embolism: Causes, Types, and Treatments
Deep vein thrombosis (DVT) in the legs is the main cause of PE. PE symptoms vary greatly, depending on the severity. Some people have no symptoms, or they experience only symptoms of DVT.
Testing is necessary because it is difficult to diagnose a PE based on symptoms alone. Treatment aims to dissolve, remove, or limit the growth of the blood clot. This may involve medication, minimally invasive procedures, or even surgery in rare cases.
Each year, there are likely 900,000 cases of PEs in the United States. PEs are frequently undiagnosed so the actual incidence rate is likely higher.
This article looks at the PE types, symptoms, causes, treatments, and how doctors diagnose it.
A PE is a condition that occurs when an artery in the lung becomes blocked. DVT is the main cause of PEs. In a DVT, a blood clot (thrombus) forms in the large veins of the legs, hip, pelvis, and sometimes an arm.
The thrombus can break free and become an embolus, which travels through the bloodstream to the heart and lungs. In the lungs, it can completely block the pulmonary artery or one of its smaller branches in the left or right lung. This blocks blood flow to the area of the lung.
A PE can also block or restrict blood flow and oxygen throughout the body. This can lead to life threatening complications.
Seek immediate medical care (call 911) for serious symptoms, such as chest pain, sweating, or severe difficulty breathing. Those symptoms may occur with leg pain or swelling and sharp pain in the lungs.
Venous thromboembolism is an overarching term that refers to blood clots that have formed in a vein. This disorder includes both DVT and PE.
Doctors classify PEs based on severity and location.
The severity of a PE relates to the risk of serious complications or death. It is measured as low, moderate, or high. Doctors use several criteria to determine the severity:
- lung function
- blood pressure
- blood test results
- oxygen requirements
- imaging exam results, especially echochardiogram results
Doctors may also refer to a high risk case as a “massive” PE and an intermediate-risk case as a “submassive” PE.
Location refers to where the clot is lodged in the lung. Doctors classify three types of PE by location:
- Saddle PE: In this type, a clot lodges in the main pulmonary artery or one of its left or right main branches. This is a central PE.
- Lobar PE: With this type, a clot lodges in a lobar artery. Each left or right main pulmonary artery branch divides into two lobar arteries. There are two lobar arteries in each lung that supply two lobes in the left lung and three lobes in the right lung. This is also a central PE.
- Distal PE: In this type, a clot lodges in a segmental or subsegmental artery. These are the arteries that supply each segment of the lung. A segment is a subsection of a lobe. There are eight segments in the left lung and 10 segments in the right lung. This clot is a peripheral PE.
Symptoms vary from person to person, and it is possible to have a PE without any signs or symptoms. When a PE causes serious complications, symptoms can be severe and life threatening.
Since DVT is the main cause of PEs, symptoms of a DVT may warn of a possible PE. It is important to become familiar with the symptoms of both conditions and talk with your doctor about your risks.
Seek immediate medical care (call 911) for serious symptoms that may indicate a PE, including:
- sudden chest pain or pressure
- coughing up blood (hemoptysis)
- difficulty breathing
- fainting, change in level of consciousness, or lethargy
- rapid breathing (tachypnea) or shortness of breath (dyspnea)
- rapid heart rate (tachycardia)
- sharp pain in the lungs or chest that occurs with breathing
Symptoms due to deep vein thrombosis
In some cases, the only symptoms of a PE are those of a DVT. These symptoms will appear in a leg and sometimes an arm. These leg or arm symptoms include:
- cramps or achiness in the leg or arm
- pain and swelling of the leg or arm
- skin redness or discoloration in the area
- tenderness or warmth in the area
A PE is a blockage in one of the arteries of the lungs. The blockage is usually from a blood clot, but other causes exist that are less common. Blockage of an artery in the lung restricts blood flow to a portion of the lung and can limit the flow of blood and oxygen throughout the body.
The main cause of PE is DVT. DVT is a condition in which blood clots form in the large veins of the lower extremities, such as in the calf, thigh, pelvis, and sometimes in an arm.
If a blood clot breaks free from the wall of the vein, it can travel through the bloodstream and cause a PE by blocking an artery in the lungs.
Other pulmonary embolism causes
At times, something other than a blood clot can become an embolus and lodge in a pulmonary artery, causing a blockage. Less common causes of PE include:
- air bubbles
- amniotic fluid
- fat from bone marrow, usually due to a long bone fracture like the femur
- foreign body, usually from intravenous (IV) injection
- fragments from a tumor
- infected tissue
A number of factors increase the risk of developing a PE, but not all people with risk factors will develop one. Risk factors for PE include:
- Older age: The risk increases with age.
- Central venous catheters: This tubing is placed in a large vein, usually for long-term delivery of medications, fluids, or nutrients.
- Chronic conditions: These include cancer, heart or lung disease, and inflammatory bowel disease.
- High estrogen levels: The increased estrogen levels may be from oral contraceptives or hormone therapy. The body also produces higher levels of estrogen up to 3 months after giving birth.
- History of clotting disorders: This include personal or family history of DVT or PEs.
- Long periods of immobility: Many factors can limit mobility and blood flow. These can include prolonged bed rest after surgery or due to medical condition, and sitting for long periods such as on long trips by car or airplane.
- Traumatic injury: This includes trauma from a motor vehicle accident, fall, or another traumatic injury.
- Severe illness: This includes infections that may predispose someone to venous thrombosis.
- Vascular issues: These include varicose veins, or injury to a vein due to fracture or major surgery.
- Other health concerns: These include obesity or smoking.
DVT is the primary cause of PEs. As such, preventing DVT is the main way to prevent a PE. If you are at risk of either condition, your doctor may recommend the following:
- Elevate your legs as often as possible and raise the bottom of your bed during sleep.
- Maintain a moderate weight.
- Move and get physical activity, including walking very soon after surgery.
- Stop smoking.
- Take an anticoagulant for surgery, heart attack, stroke, or cancer complications.
- Use pneumatic compression during periods of immobility.
- Wear compression stockings.
For prolonged sitting or travel, it can be helpful to drink plenty of fluids, wear support stockings, take frequent standing or walking breaks, and practice calf and ankle exercises in your seat.
For people who are at higher risk for DVT — such as following orthopedic surgery — doctors may also recommend taking aspirin when traveling by airplane.
To make a PE diagnosis, your doctor will take a medical history, perform an exam, and order tests. Questions your doctor may ask include:
- What symptoms are you experiencing?
- When did your symptoms start?
- Are your symptoms constant or do they come and go?
- How severe are your symptoms?
- What, if anything, seems to make your symptoms better or worse?
- Do you have a history of blood clots, DVT, or PEs?
- Does anyone in your family have a problem with blood clots?
- What other medical conditions do you have?
- What medications do you take?
During the exam, your doctor will listen to your heart and lungs. It will also be important for your doctor to examine your legs for symptoms of DVT. This includes warmth, redness, and swelling. Tell your doctor if your leg is tender or sore.
Testing is necessary because it is difficult to diagnose a PE using symptoms alone. The symptoms can mimic several other conditions. Testing may include:
- Blood tests: These tests check levels of oxygen and carbon dioxide (CO2). These levels can show signs of inherited clotting disorders, and your blood’s clotting status, including D-dimer levels.
- Chest X-ray: This imaging text can rule out other conditions.
- Duplex ultrasound: This test checks the veins in your legs for DVT.
- Electrocardiogram (ECG): This simple test records electrical activity of the heart.
- CT scan with pulmonary angiography: This test uses contrast dye to make images of the arteries in your lungs.
- Ventilation/perfusion scan: This imaging test maps blood flow in the lungs and compares it to airflow through the lungs.
- Other imaging exams: These may include an MRI and a CT scan without pulmonary angiography.
Treatment of a PE varies greatly depending on the severity of the embolism. Treatment may include:
- medications to control the formation and growth of blood clots and restore blood flow to the lungs
- supplemental oxygen through a face mask, prongs in the nostrils, or a breathing tube
- procedures in severe or life threatening cases, or if the blood clot is very large
Medications to treat a pulmonary embolism
Depending on the underlying cause and severity of the PE, your doctor may prescribe:
- Anticoagulants: These medications thin the blood and prevent the formation or growth of blood clots. Common medications include warfarin (Coumadin), heparin, or thrombin inhibitors, such as apixaban (Eliquis).
- Sedatives and pain medications: These can make you more comfortable.
- Thrombolytics: These medications quickly dissolve large blood clots in severe or life threatening cases of PEs.
Procedures to treat a pulmonary embolism
In some cases, doctors use a catheter to remove the clot or deliver medication to dissolve the clot. Less commonly, surgery is necessary to access the clot.
In catheter-based thrombolysis, a doctor inserts a thin, flexible tube to access the blood clot. This involves inserting a catheter into a vein in the upper thigh or arm and guiding it through the vein to reach the blood clot.
When medications or other treatments are unsuccessful, doctors may recommend a vena cava filter. This is a surgically inserted device in the vena cava. It prevents blood clots in the lower extremities from reaching the lungs.
In the case of a massive pulmonary embolism, doctors may perform extracorporeal membrane oxygenation (ECMO). This type of life support involves pumping blood through a heart-lung machine to remove CO2 and send oxygen-rich blood back into the body. This allows time for the pulmonary embolism to resolve and the lungs to heal.
Complications of an untreated PE can be serious and even life threatening. You can help reduce your risk of serious complications by following your treatment plan. Complications of a PE include:
- hypoxia, which is low levels of oxygen in the blood
- permanent lung damage
- pulmonary hypertension
- organ failure or dysfunction
- recurrent thrombotic events
The current overall survival rate for PE is not known. In general, the more serious the embolism, the poorer the prognosis.
The Centers for Disease Control and Prevention (CDC) reports that 10–30% of people with a PE or DVT die within 30 days of diagnosis. Sudden death is the first symptom of PE in about 25% of cases.
Of the survivors, one-third to one-half will develop long-term complications, such as swelling or discoloration of the affected limb. About one-third will have a recurrence within 10 years.
An analysis of PE-related hospital admissions notes that about 3 in 100 people (3%) admitted to the hospital with a PE died.
A different study looks at short-term and long-term survival after PE diagnosis. It reports that 7.7% of people died within 30 days of diagnosis. The overall mortality was 40.4% at around 4.1 years after diagnosis. For massive PEs, the mortality rate was about 70%. Low risk PEs had an overall mortality rate of about 28%.
According to the 2016 study, the overall hospital admission rate for PEs increased from 1993 to 2012. However, the number of patients dying in the hospital decreased. The authors note this discrepancy may be due to more sensitive diagnostic testing, which can find less serious PEs. These types of embolisms tend to have better immediate outcomes compared with massive PEs.
A PE can be a life threatening condition that most often results from a DVT. It is possible to have a PE and not have symptoms involving the lungs. Some people only have DVT symptoms.
If you have a DVT, doctors will use diagnostic testing to find out if you also have a PE. If so, the severity of the PE will guide treatment. The severity will also give doctors information about the prognosis.