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.
Who is at risk of pulmonary embolism?
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 disrupt blood vessels
Injuries that damage veins, including injuries such as a broken leg, can increase the risk of DVT.
Medical conditions that increase the risk of clotting
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.
Pregnancy and childbirth
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.
Rare causes of pulmonary embolism
Occasionally, a pulmonary embolism does not originate from a DVT. In such cases, it could come from:
- a tumour — sometimes fragments of tumour can break off, enter the circulation and lodge in the arteries in the lungs;
- a fracture — if globules of fat are released from the bone marrow into the bloodstream;
- amniotic fluid — this fluid surrounds an unborn baby and can very rarely enter the pelvic veins and then lodge in the mother’s lungs during childbirth; or
- an air bubble — air bubbles can enter the circulation in scuba divers who get ‘the bends’, in some forms of surgery, and in serious injuries to the chest.
Symptoms of pulmonary embolism
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:
- shortness of breath (which usually comes on suddenly);
- chest pain (which may be sharp and worse when you take a deep breath, cough or eat); and
- a cough producing bloody or blood-streaked mucus.
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.
Diagnosing pulmonary embolism
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.
Treatment of pulmonary embolism
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’.
Preventing DVT and pulmonary embolism
People in hospital
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.
- Anticoagulant medicine, including low molecular weight heparins such as enoxaparin (Clexane) or dalteparin (Fragmin), heparin, fondaparinux (Arixtra), or dabigatran (Pradaxa).
- Graduated compression stockings — these stockings help prevent DVTs by applying gentle pressure to the legs and helping blood to flow.
- Get moving — getting out of bed and moving around as soon as possible to exercise your legs reduces the risk of blood clots forming.
People travelling long distances
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:
- drink plenty of non-alcoholic fluids during the flight;
- avoid drinking excessive alcohol;
- avoid taking sedative medicines;
- perform calf contraction exercises for a number of minutes each hour; and
- walk around the cabin about once an hour.
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.