Pulmonary Embolism

What is a pulmonary embolism?

A pulmonary embolism, sometimes known as PE, is a blood clot which blocks one of the vessels that supplies blood to the lungs. A pulmonary embolism occurs when part or all of the blood clot obstructs the blood supply to the lungs, and it is a life-threatening condition. In some cases, small or medium-sized clots can cause mild symptoms but larger clots can be fatal, so PE should always be treated as a medical emergency.

A pulmonary embolism is a type of venous thromboembolism, which is when a blood clot develops in the vein. In most cases, pulmonary embolisms develop as a result of a clot breaking away and travelling from the deep veins in the legs to the lungs via the bloodstream.

What causes a pulmonary embolism?

A pulmonary embolism develops when a blood clot travels from the deep veins in the legs up into the lungs. In most cases, this occurs as a result of deep vein thrombosis (known as DVT).

The main causes of blood clots include:

  • Inactivity: inactivity causes the blood to flow slowly and collect in the lower part of the legs. In most cases, moving again will speed up the flow of blood, but if you are inactive for a long time – for example, if you go on a long plane journey or you are recovering from an operation or serious illness – this will increase the risk of a clot forming.
  • Damage to the blood vessels: if the wall of the blood vessel is damaged this can cause it to become narrower or blocked, increasing the risk of a clot forming. There are various ways a blood vessel could be damaged, including surgery and injuries.
  • Medical conditions: some medical conditions increase the risk of a clot forming, including cancer, heart failure and Hughes syndrome, a rare genetic condition that affects the immune system.

Risk factors for pulmonary embolism include:

  • Age: your risk increases as you get older
  • Having a history of blood clots.
  • Pregnancy.
  • Obesity and being overweight.
  • Cancer and cancer treatment (chemotherapy and radiotherapy often increase the risk further).
  • Smoking.
  • Family history.
  • Hormone replacement therapy.
  • The combined contraceptive pill.
  • Surgery on the lower half of the body.
  • Leg fracture, as this means that the leg will be in plaster.

What are the symptoms of a pulmonary embolism?

The symptoms of a pulmonary embolism usually vary according to the size of the clot. Small clots may not cause any symptoms, while medium-sized clots can cause sudden breathing difficulties. Larger clots can cause the following symptoms:

  • Breathlessness, which comes on very suddenly.
  • Chest pain, which gets worse when you breathe in.
  • Suddenly collapsing.

How is a pulmonary embolism diagnosed?

In many cases, a pulmonary embolism develops when a patient is already in hospital. If a doctor suspects that you have suffered a pulmonary embolism, the following tests may be carried out:

  • D-Dimer test: a D-Dimer test is a type of blood test that is used to identify loose pieces of a blood clot in the bloodstream.
  • CT scan (computerised tomography scan): a CT scan can show if a patient has had a PE by highlighting a blockage in blood supply to the lungs.
  • Ventilation/perfusion test: a ventilation/perfusion test is a 2 part test, which measures air and blood flow to the lungs. If air is being supplied to the lungs but blood flow is blocked, this indicates a PE.

Treatment for pulmonary embolism


If you have a pulmonary embolism, you will be advised to start taking a type of medication known as anticoagulant. Anticoagulants thin the blood and prevent the blood clot getting any larger and also help to stop pieces of the blood clot from breaking away. The two main medications given to patients include warfarin and heparin. Heparin is usually prescribed first because it works quickly, while warfarin may be given at a later date to try and prevent another clot from forming. Heparin can be injected and there are two forms: standard heparin and low molecular weight heparin.

Both forms of heparin can cause side-effects, including:

  • Headaches.
  • Bleeding.
  • A rash.
  • Generally feeling unwell.
  • Stomach upset.

Warfarin is taken in tablet form and doctors monitor patients closely to ensure that the dose is correct. While taking warfarin it is important to keep an eye on your diet, as diet can affect the way the medication works. Warfarin is not given to pregnant women.

Preventing pulmonary embolism

You can reduce your risk of developing a pulmonary embolism by taking the following steps:

  • Stop smoking.
  • Stay active: aim for at least 30 minutes of gentle to moderate exercise 5 times per week.
  • Drink in moderation.
  • Eat a healthy, balanced diet, rich in fruit and vegetables and low in saturated fat.
  • Maintain a healthy weight.
  • Move around when you are on a flight. Make sure you get up and walk around every 30 minutes and keep your feet and legs moving.

Taking the contraceptive pill

Taking the contraceptive pill increases your risk of developing a blood clot and for this reason your doctor may advise against taking the pill and recommend an alternative form of contraception.

Can I fly if I have had PE?

If you have had a PE and you are still taking warfarin, you will need to have had stable blood test results for a long period of time and ensure that you have a sufficient supply of tablets. If you are not taking warfarin you will be advised to wear flight socks, keep your legs moving and take aspirin before you fly. If you have had a PE, you should see your doctor before you make plans to fly. You may also be advised to arrange to have a blood test while you are away.

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