Loading...
 
Pulmonary embolism

A pulmonary embolism (PE) is a blockage in one of the blood vessels (arteries) in the lungs - usually due to a blood clot. A PE can be in an artery in the center of the lung or one near the edge of the lung. 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 center of the lung, this is known as a massive PE, and is very serious.

In almost all cases, the cause is a blood clot (thrombus) that has originally formed in a deep vein (known as a DVT). This clot travels through the circulation and eventually gets stuck in one of the blood vessels in the lung. The thrombus that has broken away is now called an embolus (and can therefore cause an embolism). 

A pulmonary embolism (PE) is a blockage in one of the blood vessels (arteries) in the lungs - usually due to a blood clot. A PE can be in an artery in the center of the lung or one near the edge of the lung. 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 center of the lung, this is known as a massive PE, and is very serious.

In almost all cases, the cause is a blood clot (thrombus) that has originally formed in a deep vein (known as a DVT). This clot travels through the circulation and eventually gets stuck in one of the blood vessels in the lung. The thrombus that has broken away is now called an embolus (and can therefore cause an embolism). Most DVTs come from veins in the legs or pelvis. Occasionally, a PE may come from a blood clot in an arm vein, or from a blood clot formed in the heart. Rarely, the blockage in the lung blood vessel may be caused by an embolus 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 - such as the thigh bone (femur).
  • Foreign material from an impure injection - for example, with drug misuse.
  • Amniotic fluid from a pregnancy or childbirth (rare).
  • A large air bubble in a vein (rare).
  • A small piece of cancerous material (tumour) that has broken off from a larger tumour in the body.
  • Mycotic emboli - material from a focus of fungal infection.

Nearly all cases of PE are caused by a DVT (see above). So, people more likely to get a PE are those prone to DVTs. The risk factors for DVT are explained in a separate leaflet called Deep Vein Thrombosis. Some important risk factors are immobility, other serious illnesses, and major surgery (especially gynaecological surgery, and operations on the pelvis and legs). The risk of developing a DVT or PE in hospital can be greatly reduced by early mobilisation and medicine to help prevent a DVT or PE in those at particular risk.

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. The diagnosis is often suspected on the basis of symptoms and your medical history. For example, someone who has had major surgery, been immobile in hospital and then gets sudden breathlessness, is likely to have a PE. Various tests may be used to help confirm the diagnosis. These may include one or more of the following:

Ultrasound scan of the leg. A type of ultrasound called a duplex Doppler is used to show blood flow in the leg veins, and any blockage to blood flow. Ultrasound is useful because it is an easy, non-invasive test and may show up a DVT. If a DVT is found, then a PE can be assumed to be the cause of the other symptoms (such as breathlessness or chest pain). Treatment (with anticoagulant medication - see below) can be started immediately for both the DVT and the suspected PE. The treatment is generally the same for both. Further tests may be unnecessary in this situation.

 

However, if the ultrasound is negative, a DVT or PE is not ruled out, because some clots don't show up on ultrasound. Further tests will be needed.

Blood test for D-dimer. This detects fragments of breakdown products of a blood clot. The higher the level, the more likely you have a blood clot in a vein. Unfortunately, the test can be positive in a number of other situations, such as if you have had recent surgery or if you are pregnant. A positive test does not, therefore, diagnose a DVT or a PE. The test may, however, indicate how likely it is that you have a blood clot (the clot can be either a DVT or a PE). This can help decide if further tests are needed. A negative D-dimer result when you are at low risk of VTE means the chance of having a thrombus is extremely low. However, if your VTE risk is high, then a D-dimer test cannot rule out the possiblity of a thrombus and you will need other tests.

Ultrasound scanning of the heart (echocardiography). An echocardiogram is useful for people who may have a massive PE, as it can show the effect on the heart. If there is a massive PE then this puts strain on the right-hand side of the heart. It can be done at the bedside.

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 PE is present. See separate leaflet called Radionuclide (Isotope) Scan. 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 and the CTPA scan is the more accurate test. V/Q scans are used in some circumstances. For example, if you are allergic to the dye (contrast) used in CTPA scanning, if you have chronic kidney disease, or if CTPA is unavailable.

Patients who have features suggestive of a large/massive PE or who have worrying features, such as low blood pressure, fast heart rate and/or low blood oxygen levels, will need to be admitted to hospital. If no concerning features are present then patients can be assessed in hospital and blood samples sent off. If there is still a possibility of PE you may be started on low molecular weight heparin (LMWH) injections and sent home to then return and have further scans the next day. You will then return for the result where either treatment will stop or further treatment and advice will be given.

Anticoagulation is often called thinning the blood. However, it does not actually thin the blood. It alters certain chemicals in the blood to stop clots forming so easily. It doesn't dissolve the clot either (as some people incorrectly think). Anticoagulation prevents a PE from getting larger and prevents any new clots from forming. The body's own healing mechanisms can then get to work to break up the clot. Anticoagulation treatment is usually started immediately (as soon as a PE is suspected) in order to prevent the clot worsening, while waiting for test results. The injectable form is heparin (or similar injections called LMWHs). Standard heparin is given intravenously (IV), which means directly into a vein - usually in the arm. It is used for high-risk PEs and also in patients with certain medical problems - such as chronic kidney disease. LMWH is injected into the skin on the lower tummy (abdomen).  The tablets or syrup are often called warfarin. However, other medicines called direct oral anticoagulants are being increasingly used. This includes medicines such as rivaroxaban, apixaban or edoxaban. They are used instead of warfarin. 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. Warfarin takes a few days to work fully. Anticoagulant treatment is continued until three months after a PE in most cases. Sometimes longer treatment is advised, especially if there is a high risk of a further embolism. Your anticoagulant clinic or doctor will be able to advise you further. If you are pregnant, regular heparin injections rather than warfarin tablets may be used. This is because warfarin can potentially cause harm (birth defects) to the unborn child.

Close monitoring and possibly intensive care are needed if the patient is unwell or has a massive PE. In high risk of death patients (massive PE) thrombolysis is indicated. This is a clot-dissolving injection. Alteplase is the medication usually used; streptokinase or urokinase are alternatives. They are more powerful than the anticoagulant treatments heparin and warfarin, described above. However, there is a greater risk of side-effects such as unwanted bleeding. Unwanted bleeding would include bleeding into the brain (intracerebral haemorrhage) - this is a type of stroke.

Filters: these 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 (IVC). 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 bedside. Filters are useful if anticoagulant treatment on its own is insufficient, or for patients who cannot have anticoagulant treatment for some reason.

Surgery (embolectomy): in some cases, it may be possible to remove the embolus surgically. This is called embolectomy. This is a major 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. The operation carries a significant risk of death. However, it would only be considered as an option if you had a massive PE which, in itself, gave a high risk of death if it were not treated. Surgery may also be used in place of anticoagulant 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) has (rarely) been used in some cases to treat a massive PE.

Treating the clot through a fine tube (catheter): this type of treatment is called catheter embolectomy or catheter fragmentation of the clot. It involves threading a 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 break it up (fragment it) using treatment given through the tube. This is highly specialised treatment and so is only available at certain hospitals.

There is an increased risk of PE at any stage of the pregnancy until six weeks postnatally. Any symptoms of DVT or a PE in a pregnant or postnatal woman should be taken seriously and investigated immediately. Treatment in pregnancy is with heparin injections rather than warfarin tablets. This is because warfarin can potentially cause harm (birth defects) to the unborn child. For a massive PE 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 postnatally, whichever is longer.