Pulmonary Embolism

Respiratory PE

A blockage in a lung artery — almost always a clot that travelled from a deep vein — that can strain the heart and starve the lung of blood.

Educational summary only — not medical advice, and no substitute for assessment by a clinician. Diagrams are simplified illustrations.

A clot (often a piece of a leg DVT) wedges in a lung artery, cutting blood flow to that part of the lung.

Overview

A pulmonary embolism is a sudden blockage of one of the arteries supplying the lungs. In almost all cases the blockage is a blood clot that broke loose from a deep vein elsewhere — usually the leg (a DVT) — and was carried up through the heart into the lungs. PE and DVT are two ends of the same disease, called venous thromboembolism.

How the system normally works

Blood low in oxygen returns to the right side of the heart, which pumps it through the pulmonary arteries into the lungs. There it picks up oxygen and offloads carbon dioxide before returning to the left heart to be pumped around the body.

What goes wrong

A travelling clot lodges where a lung artery narrows. Two problems follow. First, blood can't reach that part of the lung to collect oxygen, so oxygen levels fall. Second — and most dangerous — the right side of the heart must suddenly pump against a blocked, high-pressure circuit. A large clot can overwhelm the right heart and cause collapse.

Diagram of a clot travelling from a leg vein up through the right heart into the lung arteries. — Most lung clots begin as a leg DVT, travel up the veins and through the right heart, then jam where the lung arteries narrow.

Symptoms and why they happen

Sudden shortness of breath — blocked blood flow and falling oxygen.
Sharp chest pain, worse on breathing in — irritation of the lung lining beyond the clot.
Fast heartbeat — the heart compensating.
Cough, sometimes with blood.
Light-headedness or fainting — a sign of a large, dangerous clot.
Often a swollen, painful leg from the original DVT.

Causes and risk factors

The same as DVT: recent surgery or immobility, long-haul travel, cancer, pregnancy, estrogen-containing contraception, obesity, smoking, and inherited clotting disorders.

How it's diagnosed

Clinical risk scoring and a D-dimer blood test guide testing. The definitive test is a CT pulmonary angiogram (CTPA), a contrast scan that shows clot in the lung arteries. Oxygen levels, an ECG, and heart strain markers (and sometimes an echocardiogram) help judge severity.

Diagram of a large pulmonary embolism straining the heart, with an enlarged right ventricle pumping against a blocked lung artery. — A large clot forces the heart's right side to pump against a blocked pipe; severe cases strain and enlarge the right ventricle — the main cause of collapse.

Treatment and management

Most people are treated with anticoagulation to stop the clot growing while the body breaks it down. Large, life-threatening clots causing low blood pressure may need clot-busting drugs (thrombolysis) or a procedure to remove or break up the clot. Oxygen and supportive care are given as needed.

Possible complications

A massive PE can be rapidly fatal. Survivors occasionally develop chronic high blood pressure in the lung arteries (chronic thromboembolic pulmonary hypertension).

Prevention and outlook

Prevention mirrors DVT: movement around surgery and travel, and blood thinners when at high risk. With prompt treatment most people recover well; the duration of anticoagulation depends on whether a clear, reversible cause was found.

When to seek emergency care

Sudden breathlessness or chest pain — especially with a swollen leg — needs emergency assessment.
Fainting, severe breathlessness, or blue lips — signs of a large, life-threatening clot. Call emergency services.