Pulmonary embolism

A pulmonary embolism (PE) occurs when a blood clot lodges in one of the arteries supplying the lungs, blocking blood flow. Most often the clot forms first in the deep veins of a leg (a deep vein thrombosis), then breaks off and travels through the heart into the lungs. This strains the right side of the heart and impairs the lungs' ability to oxygenate the blood. The risk is increased by anything that slows blood flow or makes it clot more readily: recent surgery or immobility, long journeys, a serious illness or cancer, pregnancy and the weeks after childbirth, the contraceptive pill or hormone therapy, and inherited or acquired clotting tendencies (thrombophilia). Typical symptoms come on suddenly — breathlessness, sharp chest pain that is often worse on breathing in, a fast heart rate, and sometimes coughing up blood, light-headedness or collapse. A large PE can cause a dangerous drop in blood pressure and is life-threatening. Diagnosis uses the clinical picture with a D-dimer blood test (useful mainly to help rule it out) and a CT scan of the lung arteries. Treatment is with blood-thinning medication, and, in severe cases, clot-dissolving treatment. Recognised and treated promptly, most people recover well.

• D-dimer — a breakdown product of clot; a normal level helps rule out PE in lower-risk people, but a raised level is non-specific and needs imaging to confirm.
• Troponin — can rise when a large clot strains the heart; helps gauge severity.
• NT-proBNP — also reflects strain on the heart from a significant PE.
• Oxygen level and blood gases — often show reduced oxygen.
• A CT pulmonary angiogram — the definitive test that confirms the clot.

• Sudden breathlessness
• Sharp chest pain, often worse on breathing in
• A fast heart rate
• Coughing, sometimes coughing up blood
• Light-headedness, dizziness or fainting
• A swollen, painful leg (a possible source clot)
• In severe cases: collapse, very low blood pressure