A pulmonary embolism (PE) is a blood clot in your lungs. The clot often forms in the deep veins of the legs. This condition is known as deep vein thrombosis (DVT). If the clot breaks loose and moves through the bloodstream, it’s called a venous thromboembolism (VTE) and may represent a life-threatening condition. A PE is usually a VTE that travels from the leg to the lungs.

If you don’t get effective treatment for it, a PE can lead to pulmonary hypertension. This is a condition in which blood pressure in the arteries of the lungs increases to an unhealthy level. It also strains the right side of the heart . When the heart has to work harder than normal for a long time, it can result in heart failure.

A majority of VTE cases develop during or after a stay in the hospital, usually after surgery. Many of these blood clots can be prevented with proper care in the hospital and at home after surgery.

When a clot blocks a pulmonary artery, one of the first symptoms is shortness of breath. A PE can also cause unusually rapid breathing. You might also feel chest pain with a PE.

A blood clot in the lungs can also reduce blood flow to the brain, making you feel a little lightheaded.

Read more: What does it feel like when you have a blood clot? »

PE has many possible causes. The most common cause is prolonged bed rest. When you don’t walk or move your legs for long periods, blood doesn’t circulate as well as it should. Blood pools or collects in the veins and blood clots can form. Less common causes include bone marrow from a long, broken bone, as well as tissue from a tumor, and even air bubbles.

The veins are the blood vessels that return blood to the heart. If a clot from a deep vein reaches the heart, the next stop is the lungs, where blood receives oxygen and gets rid of carbon dioxide. The blood vessels get very small. That can cause the clot to lodge in the vessel, blocking blood flow through the lungs. Normally, the oxygenated blood returns to the heart and the heart pumps the blood to the entire body. However, the clot blocks part of the return.

Any surgery that requires you to lie in bed can raise your risk of a PE. Some operations are particularly risky, however. These include pelvic, hip, or knee surgery. The risk with these operations isn’t just extended time in bed. The position necessary for the surgery may increase the risk of DVT and PE.

Other risk factors include the following:

  • A leg fracture or other injury that requires the legs to be immobile for a while can also raise your risk of a clot forming in your leg and possibly traveling to your lungs.
  • Some forms of cancer, including lung, pancreatic, and ovarian cancers, cause the body to create a substance that increases the likelihood of blood clots.
  • If you’re a smoker, you’re at an increased risk for a PE.
  • Being overweight, including pregnancy, is another risk factor.
  • Birth control pills and hormone replacement therapy can also put some women at higher risk.

If you have heart or lung disease, it can make it more difficult to diagnose PE. You may need a combination of a blood test and some imaging screenings to confirm a suspected PE.

A blood test that looks for a substance called D-dimer is one of the first tests you’ll take. It can indicate whether your blood is clotting somewhere. Recent surgery, pregnancy, and even advanced age can raise your level of D-dimer, so this test isn’t always effective.

A chest X-ray can’t always identify a blood clot in the lungs, but it can help eliminate other possible reasons for your symptoms. A CT scan can give your doctor a very detailed look at the blood vessels in your lungs.

One of the first treatments for pulmonary embolism is anticoagulation therapy. You’ll probably start taking blood thinners immediately after receiving a PE diagnosis. These may not necessarily break up or eliminate the existing PE, but they will help prevent future clots from forming. Bleeding issues are the main side effects.

In time, your body may cause the blood clot to break apart and your bloodstream may absorb it. If this doesn’t happen, you may need a procedure in which your doctor threads a catheter from a leg artery to the site of the clot. Once the catheter reaches the embolism, they seize the clot using a tiny device at the end of the catheter and remove it from the lungs.

If you have a severe case, your doctor can perform a surgical procedure called a pulmonary thromboendarterectomy (PTE) to remove clots from the larger blood vessels in the lungs.

If your doctor identifies PE early, they can effectively treat it. Approximately one-third of people with an undiagnosed, untreated PE die. That means you must take your symptoms seriously. See your doctor immediately if you’ve had surgery and you experience the symptoms of PE or the symptoms of a blood clot in your leg, including:

  • swelling
  • pain
  • tenderness
  • warmth

Once your doctor breaks up or removes the blood clot, your lung health and blood pressure should return to normal.

Many people who have one blood clot can have more than one. If you pay attention to symptoms and exercise your legs, you may be able to avoid blood clots in your lungs or elsewhere in your body.

If you’re going to have surgery, talk to your doctor about your risk of PE and what you can do to avoid it. They may give you a blood-thinning, or anticoagulant, medication, such as heparin, warfarin (Coumadin, Jantoven), or a warfarin alternative, before and after surgery. These drugs help keep blood clots from forming in the body, but they can raise the risk of bleeding complications.

If your doctor prescribes a blood thinner, you’ll most likely continue it at home. When your doctor discharges you from the hospital after your surgery, make sure you fill your prescribed blood thinners promptly. If they don’t give you a prescription for anticoagulant medications, ask them about it. As long as your risk remains high in the days and weeks after surgery, you should expect to take a daily blood thinner.

Other important ways to avoid a PE include the following:

  • Quit smoking if you smoke because it can damage your blood vessels and increase your odds of developing blood clots, high blood pressure, and other problems.
  • If you’re overweight or obese, talk with your doctor about strategies to lose weight and keep it off.

You should also treat exercise as something you do throughout the day, and not just as a 30-minute workout. The more time that you’re on your feet walking, dancing, or otherwise moving, the less likely it is that blood will have the chance to pool and clot in your legs.