Pulmonary Embolism

What is pulmonary embolism?

Pulmonary embolism is a life-threatening condition occurring in more than 600,00 people in the U.S. each year when a blood clot forms in part of their body, typically the legs (as a complication of deep vein thrombosis), and breaks off to travel to and lodge in one of the small blood vessels of the lungs.  A blocked blood vessel in the lungs is a medical emergency that can occur suddenly and cause symptoms immediately and death within an hour.

What causes pulmonary embolism?

Ninety percent of pulmonary embolisms occur as a complication of a condition called deep vein thrombosis.  When these two conditions occur together, doctors refer to the combination as venous thromboembolism.  Deep vein thrombosis involves blocked circulation in a leg due to a clot that has lodged in one of the deep, large veins.  When one of these clots or a piece or pieces of them breaks off and travels back through a vein to the heart and out to the lungs, it can lodge in an artery supplying the lungs.  Blood clots from elsewhere in the body or other substances like fat globules, tumor tissues, or bacterial clumps can travel to the lungs and block blood vessels as well. 

What are the risk factors for pulmonary embolism?

People who have or are at risk for having deep vein thrombosis are at risk for pulmonary embolism, in addition to people who have previously had a pulmonary embolism.  Risk factors for deep vein thrombosis include inherited blood clotting disorders; damaged deep veins; decreased blood flow in the legs from prolonged sitting, standing, or immobilization; cancer and cancer treatment; varicose veins; pregnancy; age greater than sixty; obesity; birth control pills or hormone therapy; recent surgery; heart disease; previous stroke or heart attack; and having a central venous catheter.

What are the symptoms, dangers, and complications of pulmonary embolism?

Sixty thousand (60,000) people (10% of those who have pulmonary embolisms in the U.S.) die due to this condition, with most of these people dying within an hour from the time of their first symptoms.  A pulmonary embolism causes problems because it can decrease blood flow to the lungs to insufficient levels, which can permanently damage parts of a patient’s lung, decrease blood-oxygen levels, and damage other organs because of inadequate oxygen supplies.  The symptoms and complications vary according to the extent of the blockage.  Large clots cause the most damage and have symptoms that are more sudden and severe.  Small clots may cause no symptoms, or cause symptoms to build gradually as the clots slowly pile up to reduce blood flow.  Symptoms of a pulmonary embolism can include shortness of breath; chest pain that increases when a patient breaths deeply, coughs, or moves his chest; and coughing up blood.  Other symptoms that are less-specific include anxiety, lightheadedness, fainting, rapid breathing, increased heart rate, a bluish tint to the skin, and excessive sweating.

How do doctors diagnose pulmonary embolism?

A patient history and physical examination may lead a doctor to suspect a pulmonary embolism.  He will take note of any risk factors for pulmonary embolism and deep vein thrombosis.  He will pay special attention to a patient’s legs—to look for signs of deep vein thrombosis—as well as to his heart rate and blood pressure because an elevation in these can indicate that the heart is having to work harder than usual in order to compensate for lungs that are not functioning properly. 

Some tests may be helpful in determining what is causing problems and confirming a diagnosis.  Doctors will want to look at both the heart and the lungs to confirm a diagnosis and to decide if a patient requires aggressive treatment. 

An electrocardiogram (ECG or EKG) will show the rhythm and rate of a patient’s heartbeat.  A chest x-ray will give doctors a picture of the heart, lungs, and larger arteries so that they can look for problems like a blockage in the lungs or an enlarged right ventricle (the right ventricle is one of the four chambers of the heart and is responsible for pumping blood out to the lungs).  A duplex ultrasound is a test for clots in a patient’s legs that involves using sound waves to generate a picture of the leg veins. 

Blood tests can show whether or not a patient has an inherited disorder that is causing the clots.  One blood test, an arterial blood gas measurement, can show the levels of oxygen and carbon dioxide in the blood.  This can be useful because a pulmonary embolism can decrease the oxygen level while increasing the carbon dioxide level.  Another useful blood test is called a D-dimer test.  This test measures blood levels of a protein that is released when a clot is dissolving in the blood.  If this measurement is high, a clot is present, while if it is normal, it is unlikely that a patient has a pulmonary embolism.  A doctor may want to see the level of cardiac troponin in the blood because an elevated level can indicate damage to the heart. 

A ventilation-perfusion lung scan (VQ scan) shows the blood flow to the lungs using a radioactive material.  Pulmonary angiography is a more invasive test in which a doctor uses a small plastic tube called a catheter to inject dye into a blood vessel to take an x-ray picture that shows blood flow to the lungs.  A spiral computed tomography (CT) scan is an x-ray that also uses dye injected into a vein to see blood flow to the lungs.  Magnetic resonance imaging (MRI) is an imaging technique that uses magnets and radio waves to form a picture of the inside of the body.  An echocardiogram uses sound waves to look for clots in the heart and make observations about heart function; doctors may use this test to see if a patient’s symptoms are the result of another condition as well as to look for right ventricular enlargement and dysfunction. 

What are the treatment options for patients with pulmonary embolism?

Timely treatment with blood thinners like heparin is often critical to stop the clot from increasing in size and prevent other clots from forming and blocking circulation around the lungs.  Treatments for pulmonary embolism can include drugs; emergency clot-dissolving treatments; procedures aimed to restore adequate blood flow and prevent future clots; as well as simple, preventative measures aimed to reduce the risk of a recurrence.

The most common medicines used to treat pulmonary embolisms are anticoagulants (blood thinners).  These drugs deprive the blood of ingredients necessary to form blood clots, but they do not break up clots that have already formed.  The body gradually dissolves clots by itself.  So, if expedience is not critical, doctors use anticoagulants, because, by preventing blood clots from growing, they use the body’s own mechanism to slowly clear blockages.  Warfarin (coumadin) is an oral anticoagulant that takes 2-3 days to begin working, while heparin is an intravenous treatment that acts immediately.  Thrombin inhibitors are new medications that prevent clotting in patients who cannot take heparin.

In emergency situations, doctors may inject thrombolytic medications by a catheter at a severely blocked point to quickly dissolve a large clot and restore blood flow.  Blood clots may also be surgically removed in an invasive, open surgery called pulmonary embolectomy or extracted in a minimally-invasive, catheter-based procedure called suction thrombectomy. 

Sometimes, other treatments are necessary.  Vena cava filters are filters that surgeons can place in a large vein to filter out blood clots before they can enter the heart from venous circulation.  These filters catch blood clots from the legs before they can be pumped to the lungs, and doctors may use them when medication is either ineffective or not an option.  Compression stockings can help prevent blood from pooling in the legs and clotting.

Doctors may be able to help a patient prevent pulmonary embolism by treating deep vein thrombosis.  Some easy steps to prevent a future pulmonary embolism may involve wearing sleeve-like devices called pneumatic compression devices that rhythmically squeeze legs during and after future surgeries until a patient has recovered and can walk again.  Patients should walk around or flex their legs every hour on plane rides or car trips to help prevent blood from pooling and should regularly exercise to promote a healthy heart and good circulation.  Obese patients should lose weight, and smokers should quit smoking to reduce their risk for recurrence.