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Air embolism

An embolism can happen when something solid, semi-solid or gaseous is travelling in your bloodstream and gets stuck. The material that should not be there is called an embolus. The most common type of embolus is a clot of blood, but other things can cause an embolism too. Examples include crystals of cholesterol, clumps of infected cells, fat, bits of bone marrow, or a gas such as nitrogen or air.

An air embolism is when bubbles of air are in the circulating blood. Air is made up of three main types of gases: oxygen, carbon dioxide, and nitrogen. In the bends, the air embolism is a bubble of nitrogen. In other air embolisms, not caused by diving, the bubble contains a normal mix of air gases.

An embolus in an artery is travelling in a system of tubes that are getting gradually smaller, so there is bound to be a point at which it blocks a small artery. This is always serious because it cuts off the blood supply to some area, but its effect will depend on the part of the body to which the artery supplies blood. It could, for instance, be part of your brain. When blood supply is lost, tissues are starved of oxygen, causing them to die. If this happens in your brain, it can cause permanent brain damage.

If the embolus is in a vein, the tube system widens along the direction of the blood flow, so a small embolus doesn't do much harm until it gets through the heart (after which it enters an artery).