Pulmonary embolism happens when a blood clot blocks one of the arteries in the lungs. This can occur when part of a blood clot that has formed in a deep vein, usually in the leg (called a deep vein thrombosis, or DVT), breaks off and travels via the bloodstream to lodge in an artery in the lung. The blood clot is then called a pulmonary embolus. Pulmonary embolism can be life-threatening if the clot is large or if there are many clots.
Pulmonary embolism is uncommon in the general population. People most likely to have a pulmonary embolism are those with risk factors for DVT. There are several risk factors for DVT.
The risk of DVT increases as you get older.
Some operations have a high risk of DVT, especially major abdominal surgery and orthopaedic surgery, including operations to replace large joints such as the hip and the knee.
People who are confined to bed after major surgery, serious illness or injuries are at an increased risk of DVT. Recently there has been much focus on how sitting in a cramped position on long plane flights and car trips can increase the risk of DVT.
Injuries that damage veins, including injuries such as a broken leg, can increase the risk of DVT.
Examples include some types of cancer, diseases of the heart and blood vessels (cardiovascular disease), inflammatory bowel disease (ulcerative colitis or Crohn’s disease), and certain inherited conditions that make the blood clot more easily and hence increase the risk of DVT.
Carrying excess weight increases the risk of blood clots and therefore DVT.
Your blood is more likely to clot when you are pregnant than when you are not. This is because levels of clotting factors (proteins in the blood that help your blood to clot when necessary) are increased and because the growing uterus (womb) can disrupt blood flow in the veins. In the period immediately after childbirth the risk of DVT is even higher than it is in pregnancy; this is especially true after Caesarean section.
The combined (oestrogen and progesterone) oral contraceptive pill and combined hormone replacement therapy (also called hormone therapy) increase the risk of DVT.
Smoking increases the risk of DVT, especially if you also have other risk factors.
Occasionally, a pulmonary embolism does not originate from a DVT. In such cases, it could come from:
Pulmonary embolism doesn’t always cause symptoms, and symptoms can vary from one person to another. The severity of symptoms depends on the size of the clot, how much of your lung is affected, and your overall health.
Pulmonary embolism can result in:
Some people experience light-headedness or fainting, confusion, or a rapid or irregular heartbeat. In severe cases, when much of the lung’s circulation is disrupted, the person may collapse and go into shock.
There may be symptoms and signs of a DVT that was the source of the embolism. DVT can cause swelling, pain, redness or warmth of the leg, and possibly a mild fever.
To look for a pulmonary embolus, your doctor may organise a chest X-ray, a lung scan called a ventilation-perfusion scan, or a helical (spiral) CT scan.
They may also look for a DVT in your legs using a special type of ultrasound to examine the blood flow in your veins, and do a blood test to measure D-dimer, a substance produced when the body breaks down blood clots.
If a diagnosis can’t be confirmed after these tests, a pulmonary angiogram may be done. In this test, a tube is inserted into a large vein (usually in the groin) and threaded through your heart to the arteries in the lungs. Dye is then injected to show the blood flow in your lungs.
People with pulmonary embolism are usually treated in hospital and often require oxygen and pain relief medicines.
The main treatment for pulmonary embolism is anticoagulant (anti-clotting) medicines. Anticoagulant medicines prevent existing clots from enlarging and additional clots from forming. Generally, injections of anticoagulant — heparin or low molecular weight heparin — are given first because they act rapidly, followed by anticoagulant tablets such as warfarin (Coumadin, Marevan) or phenindione (Dindevan), which take longer to work.
If the pulmonary embolism is large and life-threatening, you will probably be treated in an intensive care unit. You may be given a treatment called thrombolysis to dissolve the clot. This involves injections of medicines (popularly known as ‘clot-busters’) such as alteplase (Actilyse) or streptokinase (Streptase). Occasionally, surgery (thrombectomy) is performed to remove the clot.
In some cases, a filter may be inserted into the major vein that takes blood back to the heart from the lower body (the inferior vena cava) to prevent any further clots from reaching the lungs. This type of filter is usually only inserted if you are unable to take anticoagulants, or if you have had ongoing problems with clotting despite being treated with anticoagulant medicines.
After a pulmonary embolism, you will probably have to remain on anticoagulant medicines for at least 3 to 6 months, possibly indefinitely if you are thought to be at high risk of having another pulmonary embolism. Your doctor can advise you on the risks and benefits of long-term anticoagulant treatment, so that together you can make the best decision for your particular circumstances. You will need to have regular blood tests while being treated with anticoagulant medicines to make sure that your blood is adequately ‘thinned’.
Because people in hospital are often inactive, many are at risk of developing a DVT. To help prevent DVT and pulmonary embolism in hospital patients who are at risk of DVT, such as those having major operations, doctors recommend the following measures.
People travelling on long-haul flights or other forms of transport (such as car, bus or train) where they are exposed to prolonged seated immobility may be at increased risk of developing blood clots.
All passengers taking a long-haul flight (more than 5 hours), are advised to:
If you are travelling by air and are considered to have a higher than average risk of clotting (e.g. you have a previous history of DVT or other risk factors for DVT), you may be advised to wear knee-length compression stockings (sometimes called ‘flight socks’). Some people may also be advised to take anticoagulant medicines before flying. Check with your doctor if you think you may be at increased risk.
Last Reviewed: 31 March 2010