Pulmonary embolism

About pulmonary embolism

A pulmonary embolism happens when a blood clot or a piece of a blood clot gets stuck in one of the blood vessels in your lungs. The clot forms somewhere else in your body and is carried to your lungs in your blood. It usually forms in one of the deep veins in your legs. This is called deep vein thrombosis (DVT).

Symptoms of pulmonary embolism

Symptoms of a pulmonary embolism include:

  • chest pain
  • breathlessness and coughing
  • fainting
  • coughing up blood

The symptoms you have and how severe they are will depend on how big the pulmonary embolism is. A small embolism may not cause any symptoms. However, a large embolism can cause shock and sudden collapse.

These symptoms are not necessarily a result of a pulmonary embolism, but if you have any of them you should see your GP. If your symptoms are severe, call for emergency help.

Causes of pulmonary embolism

Most pulmonary embolisms are a result of DVT in your leg. DVT can develop if you're inactive for a long period of time.

You're more likely to get DVT and therefore a pulmonary embolism if you:

  • have recently had major surgery, particularly on your hip or knee
  • are pregnant or have recently had a baby
  • have cancer
  • are confined to bed with a serious illness
  • have had DVT or a pulmonary embolism before
  • have an inherited condition called thrombophilia, which means you're more likely to get blood clots
  • have heart disease or other serious long-term illness
  • take the combined contraceptive pill or hormone replacement therapy (HRT)
  • are travelling for a long distance and aren’t able to move around much
  • are obese
  • smoke

Diagnosis of pulmonary embolism

If you visit your GP with minor symptoms, he or she will ask about your symptoms and medical history, and examine you. If you have more severe symptoms, for example, having trouble breathing or you collapse, you will need to go to hospital urgently.

If your GP thinks you may have had a pulmonary embolism, he or she will refer you to hospital. You may have an electrocardiogram (ECG) to rule out other conditions. An ECG measures the electrical activity in your heart to see how well it's working.

Tests commonly used to diagnose a pulmonary embolism include the following.

  • Blood tests, including a test for a substance called D-dimer. If the test result is negative, this can rule out DVT and a pulmonary embolism.
  • Computed tomography pulmonary angiography (CTPA) – this test uses X-rays to make a three-dimensional image of your lungs. A dye is injected into your veins so that they show up on the X-ray image.
  • Isotope lung scanning. This test can see how much blood is getting into your lungs. It's sometimes done before a CTPA.
  • Chest X-ray, although this doesn’t always show a problem.
  • An ultrasound scan of your legs, to look for DVT.

Treatment of pulmonary embolism

Your doctor may give you injections of a medicine called heparin before your diagnosis has been confirmed. Heparin is an anticoagulant used to prevent blood clots forming, or to stop blood clots getting worse. If your doctor thinks you have a life-threatening pulmonary embolism, you may be given an injection of a thrombolytic medicine (eg alteplase), which helps dissolve fresh blood clots.

If a pulmonary embolism is confirmed, your doctor will prescribe ongoing treatment with an anticoagulant that you take by mouth, such as warfarin. You will usually need to take this medicine for three to six months, or sometimes longer. If you develop an embolism twice for no obvious reason, or are felt to be at high risk of another, you may need lifelong treatment.

Your doctor may suggest putting a filter into the main vein carrying blood to your heart (the inferior vena cava) if, for example, you're at high risk of getting another pulmonary embolism or you can't take anticoagulant medicines. The filter stops any other clots travelling up to your heart and lungs.

Special considerations

If you're pregnant

You’re at a higher risk of a blood clot when you're pregnant. This risk is further increased if you have pre-eclampsia (a condition that affects pregnant women and causes high blood pressure), a long labour or a caesarean delivery.

If you or members of your close family have had DVT or a pulmonary embolism in the past, you may be offered screening for a blood clotting disorder (thrombophilia).

If your doctor thinks you're at high risk of getting a blood clot, he or she may offer you heparin injections during your pregnancy and for six weeks after you have given birth. He or she may also recommend you wear elastic compression stockings.

Prevention of pulmonary embolism

If you're in hospital for an operation or because of illness, the staff will assess your risk of developing DVT. Your doctor may suggest some exercises to keep your legs moving. You will be encouraged to drink enough fluids, or you may be given fluids through a drip if you're unable to drink, so that you don’t become dehydrated.

If you're at high risk of DVT, you will be given daily injections of heparin and your doctor or nurse may recommend that you wear compression stockings to help your circulation. Compression stockings come in different sizes and your nurse will check yours are the right fit for you. You might be asked to wear them after you have had surgery.

Alternatively, you may be fitted with an intermittent pneumatic compression device. This device inflates regularly, putting pressure on your legs to keep the blood flowing.

If you're having major surgery, you’re likely to have injections of heparin after your operation to reduce your risk of getting DVT or a pulmonary embolism. You may need to have these injections for up to six weeks. Alternatively, you may have an anticoagulant medicine that you can take by mouth.

What is the risk of getting a pulmonary embolism when taking the combined contraceptive pill?


Women taking the combined contraceptive pill have a three- to five-fold increase in risk of getting deep vein thrombosis (DVT) or a pulmonary embolism. This is by comparison to healthy women who aren’t pregnant or taking the combined contraceptive pill. However, the actual numbers of women affected are still small.


Combined oral contraceptives contain a synthetic version of oestrogen, usually ethinylestradiol, plus one of several types of progestogen, which is a synthetic version of progesterone.

Although you may be at an increased risk of getting DVT or a pulmonary embolism if you take the contraceptive pill, it's still rare to get one of these conditions.

However, your overall risk may be much higher if you take the combined contraceptive pill and have other risk factors for DVT and a pulmonary embolism, such as having a blood clotting disorder or having a personal or family history of DVT. Because of this, your doctor will ask you about your medical and family history before you start taking the contraceptive pill.

Women taking the combined contraceptive pill also have a slightly higher risk of getting DVT during surgery. If you're having surgery, your doctor will talk to you about the risks and benefits of stopping taking the pill beforehand. The small reduction you may get in your risk of DVT has to be balanced against the risk of unplanned pregnancy if you stop taking the pill.

It's worth bearing in mind that around one to two women in 1,000 will get a blood clot while they are pregnant or just after they have given birth.

Will I be at risk of pulmonary embolism if I take a long flight?


Flying, and long journeys in general, may increase your risk of getting a blood clot and a pulmonary embolism because you're inactive for a long period of time. However, most people who develop deep vein thrombosis (DVT) and a pulmonary embolism after a long flight also have other risk factors for these conditions.


Sitting down on a long journey means that your legs are inactive for a long time. When your legs are inactive, the blood flow slows down and blood can start to pool in your veins. This can increase your risk of getting a blood clot in your leg (DVT), which can then travel to your lungs (pulmonary embolism).

Other factors that can increase your risk of DVT and a pulmonary embolism when flying include:

  • dehydration
  • compression of the vein behind your knee on the edge of your seat

To reduce your risk of DVT when flying:

  • walk around the cabin whenever you can
  • do simple leg exercises in your seat, such as flexing your ankles
  • drink enough water so you don’t become dehydrated
  • don't drink too much alcohol or coffee (these can cause dehydration)

However, remember that most travellers who develop DVT also have other risk factors for the condition. If you're at high risk of getting DVT (eg if you're pregnant, have recently had surgery, have had DVT before or have a known thrombophilic condition) and will be travelling for more than six hours, your doctor may advise you to wear compression stockings. He or she may also advise you to have an injection of a medicine called heparin, which prevents blood clots, immediately before you travel. Ask your doctor for advice before you fly.

Could anticoagulants harm my unborn baby?


Some anticoagulants (medicines that prevent your blood clotting) could harm your developing baby, so you shouldn't take them if you're pregnant. These include the medicine warfarin. If you're pregnant and need to take an anticoagulant medicine, your doctor will usually advise you to have injections of a medicine called heparin because this is safer.


You may need to take an anticoagulant medicine while you're pregnant if your doctor thinks you're at risk of developing deep vein thrombosis (DVT) and a pulmonary embolism. Some women are given anticoagulant medicines when they are pregnant if they have a history of prior miscarriages.

Anticoagulants that you take by mouth, such as warfarin, are not suitable during pregnancy. This is because they can cross the placenta (which delivers oxygen and nutrients to the baby) and cause harm to your developing baby. If you’re taking warfarin and think that you might be pregnant, tell your doctor immediately.

Pregnant women who need anticoagulant treatment can take heparin, as it doesn't cross the placenta, so it won't reach your baby. If you were taking an oral anticoagulant, such as warfarin before you became pregnant, you will be advised to switch to a type of heparin called a low-molecular-weight heparin as soon as your pregnancy is confirmed. Heparin is taken by injection.

Sometimes you may need to continue using low-molecular-weight heparin after the birth of your baby. This may be for up to six weeks, depending on your risk of getting a blood clot.

You can take both warfarin and low-molecular-weight heparin while breastfeeding.