Pulmonary Embolism

What is a pulmonary embolism?

A pulmonary embolism is a blockage in one of the arteries (blood vessels) in the lungs - usually due to a blood clot.

What types of pulmonary embolism are there?

A pulmonary embolism can be in the centre of the lung or near the edge. The clot can be large or small and there can be more than one clot. If there are severe symptoms, which occur with a large clot near the centre of the lung, this is known as a 'massive' pulmonary embolism, and is very serious.

What causes a pulmonary embolism?

The usual cause - a DVT

In almost all cases, the cause is a blood clot that has originally formed in a deep vein (known as a deep vein thrombosis or DVT). This clot travels through the circulation and eventually gets stuck in the lung. Most DVTs come from veins in the legs or pelvis. Occasionally, DVTs can come from an arm vein, or from a blood clot formed in the heart.

A separate leaflet called 'Deep Vein Thrombosis' gives more details. DVTs and pulmonary embolism are also known as 'VTE' or 'venous thromboembolism'.

Other causes

Rarely, the blockage in the lung blood vessel may be caused by a substance which is not a blood clot. This can be:

• Fatty material from the marrow of a broken bone (if a large, long bone is broken).
• Foreign material from an impure injection. For example, with intravenous drug misuse.
• Amniotic fluid from a pregnancy or childbirth (rare).
• A large air bubble in a vein (rare).

Who gets a pulmonary embolism?

Nearly all cases of pulmonary embolism are caused by a DVT (see above). So, people more likely to get a pulmonary embolism are those prone DVTs. The risk factors for DVT are explained in a separate leaflet on deep vein thrombosis. Some important risk factors are immobility, other serious illnesses and major surgery.

What are the symptoms of a pulmonary embolism?

The symptoms will depend on how large or small the clot is, and on how well the person's lungs can cope with the clot. People who are frail or have existing illness are likely to have worse symptoms than someone who is fit and well. Symptoms often start suddenly.

A small pulmonary embolism may cause:

• No symptoms at all.
• Shortness of breath - this can vary in degree from very mild to obvious shortness of breath.
• Chest pain which is 'pleuritic', meaning pain felt when breathing in. This happens because the blood clot may irritate the lining layer (pleura) around the lung.
• Coughing up blood.
• A mild fever.

A large pulmonary embolism, or multiple emboli (lots of clots), may cause:

• Shortness of breath which may be severe.
• Chest pain - with a large pulmonary embolism the pain may be felt in the centre of the chest behind the breastbone.
• Feeling faint, feeling unwell, or a collapse. This is because a large blood clot interferes with the heart and blood circulation.
• Rarely, in extreme cases, a massive pulmonary embolism can cause cardiac arrest, where the heart stops pumping due to the clot.

There may be symptoms of a DVT, such as: pain at the back of the calf in the leg, tenderness of the calf muscles or swelling of a leg or foot.

How is a pulmonary embolism diagnosed?

The diagnosis is often suspected on the basis of symptoms and the patient's medical history. For example, someone who has had major surgery, been immobile in hospital and then gets sudden breathlessness, is likely to have a pulmonary embolism.

Various tests may be used to help confirm the diagnosis. These may include one or more of the following:

Ultrasound of the leg

This test is useful because it is easy for the patient and may show up a DVT. If a DVT is found, then anti-clotting treatment can be started immediately for both the DVT and the suspected pulmonary embolism. Further tests may be unnecessary in this situation.

However, if the ultrasound is negative, that does not rule out a DVT or pulmonary embolism, because some clots don't show on ultrasound. Further tests will be needed.

Blood test for D-dimer

D-dimer is a substance involved in the clotting mechanism of the blood. The D-dimer blood test indicates how likely it is that the person has a blood clot (the clot can be either a DVT or a pulmonary embolism). The test does not give a definite yes/no answer to the question "is there a pulmonary embolism?" - but it can help decide if further tests are needed. The D-dimer test is not useful in pregnancy, because pregnancy itself affects the results.

Ultrasound of the heart (echocardiography)

This test is useful for patients who may have a massive (large) pulmonary embolism, as it can show up large clots in the lung or their effect on the heart. It can be done at the bedside. It does not show up a small pulmonary embolism.

Isotope scan and CTPA scan

These are specialised scans which look at the circulation in the lung. They are useful, because they can show quite accurately whether or not a pulmonary embolism is present.

The isotope scan is also called a 'V/Q scan' or 'ventilation/perfusion' scan. The CTPA scan is a type of CT scan looking at the lung arteries - the full name is 'computed tomographic pulmonary angiography' scan. Both involve X-rays, so are not used unless actually needed, to avoid giving unnecessary radiation.

General tests

Other tests on the heart, lung and blood are usually done. These may help with the diagnosis or may show up other conditions.

• An ECG to check the heart.
• Blood tests to look for signs of a heart attack, infection or inflammation. Also, a test for 'arterial blood gases' may be taken, which involves taking the blood sample from an artery rather than a vein. This is to check the level of oxygen in the blood.
• A chest X-ray to look for pneumonia or other chest conditions.

What is the treatment for a pulmonary embolism?

This section deals with pulmonary embolism due to a blood clot, not with the rare causes listed above. The main treatments are:

• anti-clotting treatment
• oxygen given in the early stages

Anti-clotting treatment

This reduces the clotting process in the blood. It helps to stop the existing clot from becoming larger, and helps prevent further clots forming. The body's own healing mechanisms can then get to work to break up the clot. Anti-clotting treatment is usually started immediately (as soon as a pulmonary embolism is suspected) in order to prevent the clot worsening, while waiting for test results.

Anti-clotting medication come in two forms: injections and tablets (or syrup for those who cannot swallow tablets). The injection type is heparin (or similar injections called 'low molecular weight heparins'). The tablets or syrup are called warfarin. Outside the UK, other medicines may be used which are similar to warfarin. They all belong to the group known as 'oral anticoagulants'.

Usually, injections are used when starting treatment, because they work immediately. Once the injections are working and the diagnosis is confirmed, warfarin can be started. The warfarin takes a few days to work fully.

Note: anti-clotting treatment should be monitored with regular blood tests, to ensure the correct level of anti-clotting effect is being achieved. Most patients will be referred to a clinic called a 'warfarin clinic' or 'INR clinic' for monitoring. It is very important to attend these appointments.

Anti-clotting treatment is continued until three months after the pulmonary embolus, in most cases. Sometimes longer treatment is advised.

Supportive treatment

This means treatment to help the body cope with the effects of the blood clot.

• Oxygen to reduce breathlessness.
• In some cases, intravenous fluids are given to support the circulation.
• Close monitoring and possibly intensive care are needed if the patients is unwell or has a large pulmonary embolism.

Additional treatments

These may be used to treat a massive pulmonary embolism where the patient is very unwell, or where anti-clotting treatment cannot be given.

Clot dissolving injection
This is medication given into a vein to help dissolve the blood clot. Alteplase is the usual one used; streptokinase or urokinase are alternatives. They are more powerful than the anti-clotting treatments heparin and warfarin described above. However, there is a greater risk of side-effects such as unwanted bleeding.

Filters
Filters can be used to stop any more blood clots from reaching the lung. The filter is placed in a large vein called the inferior vena cava. The filter is inserted via a thin tube, which is put into a large vein and then fed along the vein into the correct position. This procedure does not need an anaesthetic and can be done at the patient's bedside.

Filters are useful if anti-clotting treatment on its own is insufficient, or for patients who cannot have anti-clotting treatment for some reason.

Surgery
In some cases, it may be possible to surgically remove the blood clot. This is a serious operation because it involves surgery inside the chest, close to the heart. It requires a specialist hospital and surgical team. It is generally considered as a last resort for very ill patients, although some hospitals in the USA have used surgery to treat patients who have large clots but are not so severely ill.

Surgery may also be used in place of anti-clotting or clot-dissolving treatment, for patients who cannot have those treatments. This would usually be because they were at a high risk of bleeding.

Heart-lung bypass (extracorporeal life support), rarely, has been used in some cases to treat a severe pulmonary embolism.

Treating the clot through a catheter (tube)
This type of treatment is called catheter embolectomy or catheter fragmentation of the clot. It involves threading a fine tube (the catheter) through blood vessels until it reaches the blood clot in the lung. Once the clot is reached it may be possible to remove it or fragment it (break it up) using treatment given through the tube.

This is highly specialised treatment and so is only available at certain hospitals.

Pregnancy and postnatal

There is an increased risk of pulmonary embolism at any stage of the pregnancy until six weeks postnatal. Any symptoms of DVT or a pulmonary embolism in a pregnant or postnatal woman should be taken seriously and investigated immediately.

Treatment in pregnancy is with heparin injections rather than warfarin tablets, because warfarin may affect the growing baby. For a massive pulmonary embolism where the patient is unwell, any of the 'additional treatments' listed above may be used.

Treatment in pregnancy is continued until three months after the embolism or until six weeks post-natal, whichever is longer.

Postnatally, warfarin can be started in place of heparin, once bleeding from the birth has settled. Heparin and warfarin can be taken by breastfeeding mothers. If taking warfarin and breastfeeding, it is advisable to ensure that the baby has had its routine vitamin K injection. This is because vitamin K helps counteract the effects of warfarin. (In the UK, all babies are routinely given a vitamin K injection at birth, unless parents object - because vitamin K helps prevent clotting problems in newborn babies anyway, regardless of whether the mother is taking treatment.)

What are the complications of a pulmonary embolism?

Most people with a pulmonary embolism are treated successfully and do not get complications. However, there are some possible, serious complications and these include:

• Collapse - due to the effects of the blood clot on the heart and circulation. This can cause a cardiac arrest where the heart stops, and may be fatal.
• The pulmonary embolism can cause a strain on the heart. This may lead to a condition called heart failure, where the heart pumps less strongly than normal.
• Blood clots can occur again later (known as a recurrent pulmonary embolism). Anti-clotting treatment helps to prevent this.
• Complications due to treatment. The anti-clotting treatment can have side-effects. The main one is bleeding elsewhere in the body, for example, from a stomach ulcer. About 3 in 100 patients will get significant bleeding due to anti-clotting treatment for a pulmonary embolism. Usually this type of bleeding can be treated successfully. Rarely, this type of bleeding can be fatal (in about 3 in 1000 cases of pulmonary embolism). However, it is almost always safer to take the anti-clotting treatment than not to, so as to prevent another pulmonary embolism which could be serious. Remember that if you are taking anti-clotting treatment, it should be monitored (as above).
• Rarely, if there are repeated small pulmonary emboli, they may contribute to a condition called 'primary pulmonary hypertension' (high pressure in the lung blood vessels).

What is the outlook (prognosis) for a pulmonary embolism?

This depends on the type of pulmonary embolism and on whether there are any other medical problems.

On average, if the pulmonary embolism is treated promptly, the outlook is good, and most patients can make a full recovery. The outlook is less good if there is an existing serious illness which helped to cause the embolism, for example, advanced cancer. A large or massive pulmonary embolism is also more difficult to treat.

A pulmonary embolism is a serious condition and can be fatal. Without treatment, about 3 in 10 people would die from a pulmonary embolism. With treatment the outlook is much better and about 5 in 100 people die from a pulmonary embolism.

The most risky time for complications or death is in the first few hours after the embolism occurs. Also, there is a high risk of another pulmonary embolism occurring within six weeks of the first one. This is why treatment is needed immediately and is continued for about three months.

How can a pulmonary embolism be prevented?

This involves preventing a DVT. Prevention of DVT is explained in the separate leaflets on 'Deep Vein Thrombosis (DVT)' and 'Deep Vein Thrombosis - Prevention When Travelling'.

Patients having major surgery should be assessed for their DVT risk, and patients at high risk of DVT may need preventative doses of heparin or a similar drug before and after surgery. Other preventative measures are also possible while in hospital.

Further help and information

Lifeblood

A charity dedicated to increasing awareness and prevention of thrombosis.
Tel: 020 7633 9937 Web: www.thrombosis-charity.org.uk

British Lung Foundation

73-75 Goswell Road, London EC1V 7ER
Helpline: 08458 50 50 20 Web: www.lunguk.org