Pulmonary Embolism
(Blood Clot in the Lung)

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Pulmonary embolism facts

  • Pulmonary embolism is a diagnosis that should be considered in patients with chest pain and/or shortness of breath, and is one of the causes of sudden death.
  • The diagnosis of pulmonary embolism may be difficult to make, and is often missed. Diagnostic strategies need to be individualized to each patient and situation.
  • Anticoagulation is the treatment of choice for pulmonary embolism and the patient may be required to continue treatment for months.
  • Prevention is the best treatment for pulmonary embolism, which can be accomplished by minimizing the risk factors for deep vein thrombosis (DVT).

What is a pulmonary embolism?

The lungs are a pair of organs in the chest that are primarily responsible for the exchange of oxygen and carbon dioxide between the air we breathe and blood. The lung is composed of clusters of small air sacs (alveoli) divided by thin, elastic walls (membranes). Capillaries, the tiniest of blood vessels, run within these membranes between the alveoli and allow blood and air to come near each other. The distance between the air in the lungs and the blood in the capillaries is very small, and allows molecules of oxygen and carbon dioxide to transfer across the membranes.

The exchange of the air between the lungs and blood are through the arterial and venous system. Arteries and veins both carry and move blood throughout the body, but the process for each is very different.

  • Arteries carry blood from the heart to the body.
  • Veins return blood from the body to the heart.
  • The heart is a two-sided pump.
  • Oxygen-carrying blood travels from the left side of the heart to all the tissues of the body. The oxygen is extracted by the tissue, and carbon dioxide (a waste product) is delivered back into the blood.
  • The blood, now deoxygenated and with higher levels of carbon dioxide, is returned via the veins to the right side of the heart.
  • The blood is then pumped out of the right side of the heart to the lungs, where the carbon dioxide is removed and oxygen is returned to the blood from the air we breathe in, which fills the lungs.
  • Now the blood, high in oxygen and low in carbon dioxide, is returned to the left side of the heart where the process starts all over again.
  • The blood travels in a circle and is therefore referred to as circulation.

The oxygen is carried in the red blood cell by a molecule known as hemoglobin. When this combination of oxygen and hemoglobin occurs, the blood turns brighter red. This blood oxygen saturation can be measured, either by sampling the blood from an artery or by a noninvasive device called an oximeter. This is often referred to as an “ET finger”, since the apparatus when attached to the finger glows red.

If a blood clot (thrombus) forms in the one of the body's veins (deep vein thrombosis or DVT), it has the potential to break off and enter the circulatory system and travel (or embolize) through the heart and become lodged in the one of the branches of the pulmonary artery of the lung.

A pulmonary embolus clogs the artery that provides blood supply to part of the lung. The embolus not only prevents the exchange of oxygen and carbon dioxide, but it also decreases blood supply to the lung tissue itself, potentially causing lung tissue to die (infarct).

A pulmonary embolus is one of the life-threatening causes of chest pain and should always be considered when a patient presents to a healthcare provider with complaints of chest pain and shortness of breath.

There are special types of pulmonary embolus that are not due to blood clots, but instead are due to other body materials. These are rare occurrences and include:

  • fat emboli from a broken femur,
  • an amniotic fluid embolus in pregnancy, and
  • in some cases, tumor tissue from cancer.

The signs and symptoms are the same as that of a blood clot, and is caused by blockage of part of the arterial tree of the lung, and prevents the bloods ability to reach all parts of the lung tissue.

Picture of how red blood cells and platelets form a blood clot Picture of a blood clot is formed
Reviewed by George Schiffman, MD, FCCP on 6/6/2012


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Pulmonary Embolism (Blood Clot in the Lung) - Diagnosis Question: Describe the exams and tests you received that led to a diagnosis of a pulmonary embolism.
Pulmonary Embolism - Venous Doppler Question: Did you have a venous doppler study, or ultrasound? Please share your experience.
Pulmonary Embolism - Thrombolytic Therapy Question: Did you or someone you know receive thrombolytic therapy for a pulmonary embolism? Please share your story.
Pulmonary Embolism - Symptoms Question: What symptoms did you experience with your pulmonary embolism?
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How Pie Prevents Blood Clots

Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editor: Melissa Conrad Stöppler, MD

This weekend, as I drove the five hours to the north Wisconsin woods, I reminded myself of advice I give to my patients: Remember to get out of the car and move around. It's also why, buried deep in the recesses of the in flight magazine, somewhere between the movie grid and the duty-free opportunities, hides a warning that staying still in an airplane seat for a prolonged time can cause blood clots. And while the magazine recommends moving around the cabin and stretching, the flight attendants tend to want to keep you in your seat.

Blood does wonderful things like carrying oxygen, cleaning waste products, and delivering cells and chemicals to fight infection. But mess up its environment and blood can cause all sorts of problems. Blood cells get pushed by the heart to the far recesses of the body, but it returns from the fingers, toes, arms and legs in veins that are milked by the routine contractions of the muscles that surround them. As you walk, blood gets pushed back to the heart; as you type, the muscles of your fingers and hands do the work to get the blood back.

Without that muscle movement, blood stagnates and has a tendency to clot. There are two parallel systems of veins in the legs and arms. The superficial set under the skin drains blood into the deeper set through a set of connectors that have valves in place. So clots in the superficial system are filtered before they enter the deep pipeline. No such luck for the deep vein system. No valve, no filters, and it's a straight shot to the heart and lungs if a clot should form and break off.

Deep venous thrombosis, or DVT, is the medical term for a blood clot in that deeper system. The symptoms of pain, swelling, and redness are similar to those of infection, and sometimes it's hard to tell the two apart, except by using ultrasound to check the flow of blood in the veins. But the DVT is just the harbinger (sign) of potential disaster. If a clot has formed, it can grow and break off and float downstream. Downstream means through the heart and into the lungs, where it can get lodged and make the lungs fail. A clot that breaks free and moves is called an embolus, and a pulmonary (lung) embolus is a big deal and a killer.

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