Quick answer

What is pulmonary embolism?

A pulmonary embolism (PE) is a blockage in a blood vessel in the lung, usually caused by a blood clot that has travelled from a deep vein in the leg (deep vein thrombosis). It is a medical emergency. Symptoms include sudden breathlessness, chest pain worse on breathing in, coughing up blood, and a rapid heartbeat. Call 999 if you suspect a PE. Treatment is anticoagulation — blood-thinning medicines — to stop clots growing and new clots forming.

Pulmonary embolism — a clot in the lung

A pulmonary embolism (PE) is a blockage in a lung artery, usually caused by a blood clot that has travelled from elsewhere in the body — most often a deep vein thrombosis (DVT) in the leg. Together, DVT and PE are called venous thromboembolism (VTE).

PE is a medical emergency. Large clots can stop blood flow to the lungs, strain the heart, and be fatal without prompt treatment.

Symptoms — act fast

Call 999 if you or someone else has:

  • Sudden breathlessness — may come on rapidly
  • Chest pain — sharp, worse on breathing in (pleuritic)
  • Coughing up blood
  • Rapid or irregular heartbeat
  • Fainting or feeling lightheaded
  • Anxiety or a sense of impending doom

Symptoms vary — a small PE may cause mild breathlessness, while a massive PE causes collapse.

Risk factors

  • Recent surgery — especially hip, knee, or abdominal
  • Prolonged immobility — long flights, hospital bed rest, leg plaster
  • Cancer and chemotherapy
  • Pregnancy and the first 6 weeks after birth
  • Combined contraceptive pill and HRT
  • Previous DVT or PE
  • Obesity
  • Thrombophilia — inherited clotting disorders

Diagnosis

  1. Clinical assessment — Wells score estimates probability
  2. D-dimer blood test — elevated in active clotting; normal result helps exclude PE in low-risk patients
  3. CT pulmonary angiogram (CTPA) — gold-standard imaging
  4. Leg ultrasound — finds DVT in many cases
  5. ECG and blood gases — assess heart strain and oxygen levels

Treatment

Anticoagulation — blood-thinning medicines prevent clots enlarging and new clots forming:

  • DOACs — apixaban, rivaroxaban, edoxaban, dabigatran — often started immediately
  • Heparin then warfarin — alternative pathway

Severe PE with low blood pressure (massive PE):

  • Thrombolysis — clot-busting drugs such as alteplase
  • Surgical or catheter embolectomy — rare, selected cases

Supportive care — oxygen, fluids, monitoring on a hospital ward or HDU.

Duration of treatment

Provoked PE (clear trigger — surgery, immobility) — anticoagulation for at least 3 months.

Unprovoked PE — often 6 months or longer; some patients need lifelong anticoagulation based on bleeding versus clot risk.

Prevention

  • Move regularly on long journeys — walk every 2 to 3 hours
  • Compression stockings during and after surgery
  • Prophylactic anticoagulation during hospital admission when at risk
  • Treat DVT early before clots embolise

See deep vein thrombosis for leg clot symptoms and shortness of breath when breathlessness has other causes.

Common questions

What causes a pulmonary embolism?
Most pulmonary emboli are blood clots that form in a deep leg vein (DVT) and break off, travelling through the heart to lodge in lung arteries. Less commonly, clots form in the pelvis, arm veins, or right side of the heart. Fat, air, or tumour fragments can rarely cause embolism.
What are the symptoms of a pulmonary embolism?
Sudden breathlessness — sometimes severe — is the most common symptom. Other signs include sharp chest pain worse on deep breathing, rapid heartbeat, coughing (sometimes blood), feeling faint, and anxiety. Large PEs cause collapse and cardiac arrest. Small PEs may cause milder symptoms.
How is a pulmonary embolism diagnosed?
Doctors assess clinical probability using Wells score. A D-dimer blood test helps rule out PE in low-risk patients. CT pulmonary angiogram (CTPA) is the main imaging test — shows clots in lung arteries. Leg ultrasound may find an associated DVT. ECG and blood gases support assessment.
How is pulmonary embolism treated?
Anticoagulation — blood-thinning medicines — is the main treatment. Options include apixaban, rivaroxaban, edoxaban, dabigatran, or heparin followed by warfarin. Severe PE with low blood pressure may need thrombolysis (clot-busting drugs) or surgical embolectomy. Oxygen and supportive care are given as needed.
How long do I take blood thinners after a PE?
At least 3 months for a first provoked PE (clear trigger such as surgery). Unprovoked PE or ongoing risk factors may need longer — sometimes lifelong anticoagulation. Your doctor balances clot risk against bleeding risk.
Can I prevent pulmonary embolism?
Move regularly on long journeys — walk and flex ankles. Stay hydrated. After surgery or during hospital admission, you may receive compression stockings and anticoagulant injections. Treat DVT promptly. Discuss clot risk with your doctor if pregnant, on hormone therapy, or having cancer treatment.
What is the outlook after a pulmonary embolism?
Most people recover well with treatment. A large PE can be life-threatening — early treatment saves lives. Some people develop chronic thromboembolic pulmonary hypertension (CTEPH) — breathlessness persisting months later — which needs specialist assessment.

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