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Embolism - Introduction

NHS Choices Medical Reference

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An embolism is a condition where the blood flow in an artery is blocked by a

foreign body, such as a blood clot or an air bubble


To function properly, the body's tissues and organs need oxygen, which is transported around the body in the bloodstream. If the blood supply to a major organ - such as the brain, heart or lungs - is blocked, the organ will fail (lose some or all of its function).

Two of the most serious conditions that can be caused by an embolism are:

  • stroke, where the supply of blood to the brain is interrupted or completely cut off
  • pulmonary embolism, where the blood supply to the lungs is cut off

Embolisms are a common health problem, and are a major cause of disability and death in the UK and across the world. For example, in England each year it's estimated there are 41,000 pulmonary embolisms and 120,000 strokes caused by embolisms.

What causes an embolism?

A foreign body is any object or substance that shouldn't be present in your blood. Foreign bodies that cause embolisms are known as emboli - a single emboli is called an embolus.

Blood clots

Blood contains natural clotting agents that help prevent excessive bleeding when you cut yourself.

Certain health conditions - such as obesity, heart diseasecancer or pregnancy - can cause blood clots to form even where there's no bleeding. A clot can travel in the bloodstream before being deposited in an organ or limb.


A fracture to a long bone, such as a thigh bone, can lead to fat particles within the bone being released into the bloodstream. They can also sometimes develop following severe burns or as a complication of bone surgery.


Embolisms can also occur if air bubbles or other gases enter the bloodstream.

Air embolisms are a particular concern for scuba divers. If a diver swims to the surface too quickly, the change in pressure can cause nitrogen bubbles to develop in their bloodstream. This can cause decompression sickness, which is often referred to as "the bends".

See air embolism for more information.


In people who have extensive atherosclerosis (narrowed arteries due to a build-up of cholesterol), small pieces of cholesterol can sometimes break away from the side of a blood vessel, resulting in an embolism.

Increased risk

Things that can increase your risk of an embolism include:

Treating embolisms

How an embolism is treated will depend on:

  • what caused the blockage
  • the size of the blockage
  • where in the body the blockage is

A surgical procedure called an embolectomy is sometimes carried out to remove an obstruction. During this operation, the surgeon will make a cut in the affected artery and the foreign body causing the blockage will be sucked out in a process known as aspiration.

Medication may be used to dissolve embolisms (thrombolysis) caused by blood clots. Anticoagulant medication, such as warfarin, heparin and low-dose aspirin, can help make the blood less sticky and stop further clots forming.

Embolisms caused by air bubbles are usually treated in a hyperbaric chamber. The air pressure inside the chamber is higher than the normal air pressure outside, which helps reduce the size of the air bubbles inside the diver's body.

Read more about treating air embolisms.


It's not possible to prevent all embolisms, but you can take steps to significantly reduce your risk. These steps include:

Medical Review: January 22, 2013
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