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Pulmonary embolism


A pulmonary embolism is a blood clot in the pulmonary artery, which is the blood vessel that transports blood from the heart to the lungs. It is a serious and potentially life-threatening condition as it can prevent the blood from reaching your lungs.

When the blood leaves the heart it is low in oxygen and needs to reach the lungs to pick up oxygen.

Pulmonary embolism symptoms

The signs and symptoms of a pulmonary embolism can sometimes be difficult to recognise because they can vary between individuals. However, the main symptoms include:

  • chest pain - a sharp, stabbing pain that may be worse when you breathe in
  • shortness of breath - which can come on suddenly or develop gradually
  • coughing - which is usually dry but may include coughing up blood or mucus that contains blood
  • feeling faint, dizzy, or passing out

You should visit your GP immediately if you have a combination of these symptoms.

Read more about the symptoms of a pulmonary embolism.

Causes of a pulmonary embolism

Pulmonary embolisms often occur when part or all of a blood clot travels from the deep veins in your leg up into your lungs.

A blood clot in the leg's deep veins is known as deep vein thrombosis (DVT). DVT can occur for no apparent reason, but it often develops after long periods of inactivity, such as during a long-haul flight or if you are ill in hospital.

DVTs can also occur during pregnancy, as a result of some medical conditions, such as cancer or heart failure, or if the wall of a blood vessel becomes damaged.

Read more about the causes of a pulmonary embolism.

Treating a pulmonary embolism

Pulmonary embolisms are treated with anticoagulant medicines, which reduce the blood's clotting ability and prevent blood clots from getting bigger.

You will be prescribed an anticoagulant called warfarin, which will help break down any blood clots and ensure that the blood flow to your lungs is uninterrupted.

As it can take a while for warfarin to start working, you will also be prescribed another anticoagulant called heparin. This will have an immediate blood-thinning effect and you will need to take it for the first few days.

As part of your treatment, you will also need to have regular blood tests to check that the dose of warfarin you are receiving is correct. If it is too high, you may experience bleeding, and it is too low you may have further blood clots.

Keeping mobile will also help you to maintain good blood circulation and prevent further blood clots from forming.

Read more about treating a pulmonary embolism.

Preventing a pulmonary embolism

A pulmonary embolism can sometimes occur after surgery, particularly if surgery is on the lower half of your body.

Blood vessel damage and being inactive while in hospital increases your risk of developing blood clots. Your risk is also increased if you:

  • are 40 years of age or over
  • have had a blood clot in the past
  • have a family history of blood clots
  • are overweight or obese

As well as taking warfarin while in hospital to help thin your blood, wearing compression stockings may also be recommended. They fit tightly around your lower legs and encourage the blood to flow more quickly around your body.

You can also reduce you risk of developing a pulmonary embolism if you:

Read more about preventing a pulmonary embolism.

How common are pulmonary embolisms?

In the UK, around 3-4 people per 10,000 are diagnosed with a pulmonary embolism each year. However, this is thought to be an underestimate and the actual number of cases is likely to be higher.

Studies conducted in America and Europe have found the annual incidence of pulmonary embolism to be 4-21 people per 10,000 of the population.

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Signs and symptoms of a pulmonary embolism (a blood clot in the artery that supplies blood to the lungs) include chest pain, shortness of breath and coughing.

It can be difficult to recognise the signs and symptoms of a pulmonary embolism because they can vary between individuals.

The following symptoms may occur in the order they are listed:

  • chest pain - a sharp, stabbing pain that may be worse when breathing in
  • shortness of breath - which may come on suddenly or develop gradually
  • anxiety
  • coughing - which is usually dry but may include coughing up blood or mucus that contains blood
  • sweating
  • feeling light-headed or dizzy
  • passing out 

You should visit your GP as soon as possible if you experience any combination of the above symptoms. If it is not possible for you to visit your GP, you can call NHS Direct Wales on 0845 4647 or you can contact your local out-of-hours service.

A pulmonary embolism may be suspected if you have the above symptoms and you have recently had pain in your arm or leg, or if you have any of the associated risk factors.

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A pulmonary embolism can occur when part or all of a blood clot travels through the bloodstream and becomes lodged in the pulmonary artery.

The pulmonary artery is the blood vessel that transports blood from the heart to the lungs.

Blood clots often originally develop in one of the deep veins in your legs. This is known as a deep vein thrombosis (DVT). 

Three of the main causes of a blood clot are:

  • slow blood flow
  • blood vessel damage
  • blood that clots too easily

These are described in more detail below.

Slow blood flow 

If you are inactive, blood tends to collect in the lower parts of your body, particularly in your lower legs.

This is not usually a problem because when you start to move, your blood flow increases and blood begins to move evenly around your body.

However, if you are immobile for a long period of time, the flow of blood around your body can slow down considerably.  You are likely to be immobile:

  • after a debilitating illness, such as a stroke (where the blood supply to the brain is cut off) 
  • after an injury
  • after an operation
  • when travelling on a long journey by plane, train or car

If your blood flow slows down due to a prolonged period of inactivity, your risk of a blood clot forming increases.

Blood vessel damage

If a blood vessel is damaged, the wall of the blood vessel can become narrowed or blocked. This can result in a blood clot forming.

Blood vessels can be damaged by injuries such as broken bones or severe muscle damage. If a blood vessel is damaged during surgery, a blood clot may develop, particularly in operations that are carried out on the lower half of your body.

Conditions such as vasculitis (inflammation of the wall of a blood vessel) and some types of medication, such as chemotherapy, can also lead to blood vessel damage.

Blood that clots too easily

Your risk of developing a pulmonary embolism is increased if you have a condition that causes your blood to clot more easily than normal.

Conditions that increase the likelihood of your blood clotting include:

  • cancer (cancer treatments, such as chemotherapy and radiotherapy, can also make blood clotting worse)
  • heart failure
  • thrombophilia - an inherited condition that makes your blood more prone to clotting 
  • Hughes syndrome - a condition where the blood becomes abnormally sticky, increasing its tendency to clot 

Other risk factors

Other factors that increase your risk of developing a pulmonary embolism include:

Your chances of developing a blood clot if you are taking the pill or HRT are very small and your GP will assess your individual risk before prescribing either medication.

Blood clots

Blood contains cells called platelets and proteins called clotting factors. When a blood vessel is cut, platelets and clotting factors form a solid clot at the site of the wound. The clot acts as a plug to stop the wound bleeding.

Blood clots usually only form when a blood vessel is damaged and bleeds – for example, after you've cut yourself. However, sometimes blood can clot even when a blood vessel isn't damaged. A blood clot of this type that forms in a vein or artery is called a thrombosis.

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Diagnosing a pulmonary embolism can be difficult because the signs and symptoms vary between individuals and are common to many other conditions.

Around half of all people who develop a pulmonary embolism do so while they are in hospital. The condition may be suspected if:

  • you have one or more associated risk factors, such as being over 40 years of age or having a previous blood clot
  • you have a blood clot in one of your legs, known as a deep vein thrombosis (DVT)
  • there is no other likely explanation for your symptoms

It is important that pulmonary embolisms are diagnosed correctly because treating them is not always easy and can cause side effects.

You may have some tests to check how well your lungs are working. To confirm whether a pulmonary embolism is causing your symptoms, you may have a chest X-ray.  You may also have some of the more specialised tests discussed below.

D-dimer test

D-dimer is a protein that is found in the blood after a blood clot has broken down. A D-dimer test can be used to help diagnose blood clotting abnormalities, such as thrombosis (where a blood clot develops in a blood vessel).

If a blood test reveals high levels of D-dimer, it means that pieces of a blood clot are loose in your blood stream and may have become lodged in your pulmonary artery.

Computerised tomography pulmonary angiography

During a computerised tomography pulmonary angiography (CTPA), dye is injected into the blood vessels of your lungs and a CT scan is taken.

A CT scan is a special type of X-ray that creates a very detailed image of the inside of your body. If there is a pulmonary embolism in one of your lungs, it will show up as a gap in your blood supply.

Ventilation scan

A ventilation or perfusion scan measures the amount of air and the blood flow in your lungs. If part of your lung has air in it, but no blood supply, it may be the result of a pulmonary embolism.

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If you are diagnosed with a pulmonary embolism, emergency treatment may be needed to dissolve the blood clot. You will also need medication to stop your blood clotting so easily.

About half of all pulmonary embolism cases occur while a person is in hospital. If you are not in hospital, you will be admitted so that you can receive treatment. You will be given oxygen to help you breathe comfortably.

If your pulmonary embolism is severe and life-threatening, medication to dissolve the blood clot will be prescribed. This is known as thrombolytic therapy.

The next step is to prevent further blood clots from forming using anticoagulant medicines.


As well as reducing the blood's clotting ability, anticoagulants stop blood clots from getting bigger. They can also help prevent part of the blood clot breaking off and becoming lodged in another part of your bloodstream (an embolism).

Anticoagulants are often referred to as blood-thinning medicines but they do not actually thin the blood. They alter chemicals in the blood that prevent clots forming so easily.

Heparin and warfarin are the two anticoagulants that are usually prescribed to treat pulmonary embolisms. Heparin is usually used first because it immediately prevents another clot from forming. Warfarin can take longer to start working but it is also effective in preventing further blood clots.

Heparin and warfarin as discussed in more detail below.


There are two different types of heparin - standard heparin and low molecular weight heparin (LMWH). Standard heparin is given intravenously, which means it is injected directly into a vein, whereas LMWH is injected into the skin.

If you have standard heparin you will need to be admitted to hospital so that the medication can be fed into your vein through an intravenous line. The medicinecan work differently from person to person so the dosage must be carefully monitored and adjusted if necessary.

LMWH works slightly differently to standard heparin. It contains smaller molecules which means that its effects are more reliable. A dose of LMWH can be given as one injection and you will not have to stay in hospital to be monitored.

Both standard heparin and LMWH can cause many different side effects including:

  • a skin rash
  • headaches 
  • an upset stomach
  • bleeding
  • a general feeling of being unwell
  • weakening of the bones (if taken over a long period of time).

In rare cases, heparin can also cause a severe reaction that makes existing blood clots worse and enables new ones to develop.

This reaction and weakening of your bones are less likely to occur if you are taking LMWH. Therefore, in most cases LMWH will be recommended.


Warfarin is taken in tablet form. You may need to take it for up to six months after your initial treatment with heparin to prevent further blood clots developing. In some cases, warfarin may need to be taken for the rest of your life.

As with standard heparin, the effects of warfarin vary from person to person, so you will need to be closely monitored and have regular blood tests to ensure that you are taking the right dosage.

You may need to have two or three blood tests a week when you first start taking warfarin until the correct dose is determined. After this, you may only need to have a blood test about once a month.

There are several factors that can alter the effectiveness of warfarin including:

  • your diet
  • other medication that you are taking
  • how well your liver is working

Therefore, while taking warfarin you should: 

  • keep your diet consistent
  • limit your consumption of alcohol and do not drink more than the recommended amounts (3-4 units a day for men and 2-3 units a day for women)
  • take your medication at the same time each day
  • not take any other medicine without first checking with your GP, pharmacist or anticoagulant specialist
  • avoid taking herbal medicines

As with heparin, warfarin can cause a wide range of side effects including:

  • a skin rash
  • bleeding - such as nose bleeds, rectal bleeding or blood in the urine (haematuria)
  • diarrhoea
  • fever
  • nausea and vomiting 
  • jaundice - yellowing of the skin and whites of the eyes 
  • liver problems

Read more about the side effects of warfarin.  


If you are pregnant, you will be given heparin injections instead of warfarin tablets for the full length of your treatment.

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If you are in hospital to have surgery, your risk of getting a blood clot will be assessed. Your age, medical history and the type of operation you are having will all affect your risk of developing a blood clot.

Risk factors

Your risk of developing a pulmonary embolism is raised if you are having surgery, particularly if it is to the lower half of your body.

An injury, or the surgery itself, can damage your blood vessels and being inactive while you are in hospital can cause the flow of blood around your body to slow down. These factors increase your risk of developing a blood clot.

Other factors that increase your chances of developing a blood clot include:

  • being aged 40 or over
  • having surgery on your abdomen, hips or legs and having a general anaesthetic 
  • a previous history of blood clots
  • having family members who have had blood clots
  • being overweight or obese
  • currently having cancer or having it in the past
  • having problems with your heart, lungs, bowel or joints

Preventing blood clots


If you have any of the above risk factors, your healthcare team may recommend that you take an anticoagulant medicine, such as warfarin, while you are in hospital and when you go home.

Compression stockings

Wearing compression stockings and using compression devices may also be recommended.

Compression stockings fit tightly around your lower legs and encourage your blood to flow more quickly around your body.

Compression devices are inflatable and work in a similar way, inflating at regular intervals to squeeze your legs and encourage the flow of blood.

Increasing mobility

It is very important that you increase your mobility as soon as possible by moving around or doing leg exercises.

Avoid taking long journeys for four weeks after you come out of hospital.

Smoking, diet and exercise

You can further reduce your risk of developing a pulmonary embolism by:

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