Pulmonary embolism (PE) is the sudden blockage of a blood vessel in your lung. This is a medical emergency. Not treating pulmonary embolism can be fatal because the damage to your lung can prevent oxygen from getting to the rest of your body.

PE is almost always caused by a blood clot called a deep vein thrombosis (DVT) because it forms in a vein deep inside your body. These veins run between muscles deep inside your body and carry blood to your heart and lungs. A DVT can occur anywhere in your body, but it's most common in the veins of the pelvis, thigh or lower leg. The clot can break loose and travel through your blood. It's then called an embolus. If it reaches your lungs, it's known as a pulmonary embolism.

In very rare cases, PE may be caused by an air bubble in your blood, part of a tumor that breaks off and travels through your blood, or fat from a broken bone that travels through your blood and lodges in your lung.

Symptoms of PE usually occur suddenly. If you have these symptoms, call 911 or go to the emergency room:

Difficulty breathing

Sharp chest pain that may also be felt in your back

Coughing, sometimes with blood-tinged sputum

Sweating and lightheadedness

Passing out

Blue lips or fingernails

Rapid pulse and rapid breathing

You may have symptoms of DVT before symptoms of PE so it's important to know these symptoms, too. If you have them, call your doctor right away:

  • Warmth over the area of the DVT
  • Swelling of the leg or thigh
  • Redness of the skin over the DVT
  • Pain or tenderness, especially when standing or walking

Risk factors for PE are the same as for DVT and include:

  • Having had DVT or PE before or having a family history of DVT or PE
  • Inactivity, such as being bedridden or taking long trips
  • Recent surgery or injury
  • Taking hormone replacement therapy or birth control pills
  • Pregnancy, or having recently given birth
  • Having cancer or recent cancer treatment
  • Being older than 60
  • Excessive weight
  • Having a tube inserted into a major vein for a medical treatment (central venous catheter)
  • Smoking
  • Being born with a disorder that increases blood clotting