An air embolism is an air bubble that becomes trapped in a blood vessel and blocks it. It is the leading cause of death among divers.

An air embolism can happen when a scuba diver holds their breath while they quickly surface.

When an air bubble travels along an artery, it moves through a system of blood vessels that gradually become narrower. At some point, the bubble will block a small artery and cut off the blood supply to a particular area of the body.

Read more about what causes an air embolism.

How serious is it?

The seriousness of the blockage depends on which part of the body the artery supplies blood to. For example, an air embolism in:

  • the arteries to the brain – causes immediate loss of consciousness and may lead to convulsions (fits), a stroke or heart attack
  • the coronary arteries (which lead to the heart) – may cause a heart attack
  • a blood vessel to the lungs (pulmonary embolism) – may cause chest pain and shortness of breath

If the embolism stops blood getting to the brain, tissue in the brain will be starved of oxygen and die. This can cause permanent brain damage.

Warning signs

Divers should always be carefully monitored by their colleagues and supervisors so that if an air embolism occurs, it can be immediately identified and treated.

Warning signs of an air embolism may include:

  • low blood pressure 
  • irregular heartbeat
  • extreme fatigue (tiredness) or lack of strength
  • disorientation
  • a faint blue tone to the skin caused by a lack of oxygen in the blood
  • irregular breathing
  • a lack of oxygen to the body tissues

The following symptoms of air embolism usually appear as soon as the diver reaches the surface:

  • dizziness 
  • blurred vision
  • bloody froth from the mouth
  • paralysis or weakness
  • convulsions (fits)
  • unconsciousness
  • no breathing 
  • cardiac arrest (the heart stops)

If a scuba diver loses consciousness within 10 minutes of surfacing, they probably have an air embolism and should be treated immediately.

How is it treated?

If a diver develops an air embolism the only effective treatment is immediate recompression treatment in a hyperbaric chamber.

The diver is given oxygen and laid horizontally until they reach the hyperbaric chamber.

Recompression treatment involves lying in a hyperbaric chamber, usually for several hours, and breathing a mixture of air and pure oxygen under high pressure. The treatment is effective up to 48 hours after diving. The high pressure will restore normal bloodflow and oxygen to the body's tissues and reduce the size of the air bubbles in the body.

After recompression, pressure is reduced gradually to allow the gases to leave the body without causing harm.

Air embolisms in surgery

As healthcare standards in the UK are high, air embolisms caused by surgery are rare.

In hospitals and health centres, care should be taken to prevent air bubbles from entering the bloodstream. Before injections, air should be removed from syringes and surgery should be closely monitored to ensure that air bubbles do not form in blood vessels.

Catheters or other tubes inserted into the body should be removed using a technique that minimises the possibility of air embolism.

If someone is thought to be at risk of an air embolism during surgery their blood pressure may be monitored. For example, surgery that takes place in a sitting position carries a very small risk of an air embolism.

If an air embolism is suspected during surgery, the surgeon will:

  • prevent more air from entering the body by sealing the open blood vessels
  • support the heart and lungs and treat any symptoms – for example, fluids to treat a fall in blood pressure, or drugs to treat any seizures

Air embolism mainly affects scuba divers 

Preventing an air embolism

The following advice can help avoid decompression sickness and lung damage when diving.

  • Limit the depth and duration of your dive to restrict the amount of nitrogen your body absorbs.
  • Come up to the surface slowly, with several stops on the way. This allows nitrogen to escape without causing harm.
  • Do not dive with a cold, cough or chest infection as this can increase the risk of air embolism.
  • After diving, wait for 12 to 24 hours before flying or going to a higher altitude.

Decompression sickness (the bends)

Gas bubbles can form in tissues and veins when a diver surfaces too quickly. This is commonly known as decompression sickness or 'the bends'. In some cases, this can lead to an air embolism.

Symptoms of decompression sickness include:

  • joint pain
  • itching
  • mottled skin

Treatment also involves recompression inside a hyperbaric chamber. Without treatment, there could be permanent damage.

Read more about decompression sickness.

Page last reviewed: 19/04/2013

Next review due: 19/04/2015