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

An air embolism usually happens when a scuba diver runs out of air, or if they surface too quickly and hold their breath while they come up (see Air embolism - causes for more information).

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.

How serious is it?

The seriousness of the blockage depends on which part of the body the artery supplies blood to. 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.

The symptoms of an air embolism depend on where the blockage occurs. An air embolism in an artery to the brain, for example, causes symptoms similar to those of a stroke, including confusion, partial paralysis, seizures or loss of consciousness. See Air embolism - symptoms for more information.

How is it treated?

The only effective treatment for air embolism is immediate recompression treatment in a hyperbaric chamber (see Air embolism - treatment for more information). This reduces the size of the air bubbles inside the body and restores normal bloodflow and oxygen to the tissues.

The symptoms of an air embolism depend on where the air bubble is.

For example:

• A large air bubble in the arteries to the brain will cause immediate loss of consciousness and often causes convulsions (fits). It may also cause a stroke.
• An air embolism in the coronary arteries (which lead to the heart) will cause a heart attack. A heart attack can also be caused by a large air embolism in the arteries to the brain.
• An embolism in a blood vessel to the lungs (pulmonary embolism) causes chest pain and shortness of breath.

Warning signs

Warning signs of an air embolism may include:

• low blood pressure 
• irregular heartbeat
• extreme fatigue (tiredness) or lack of strength
• blurred vision
• 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

An air embolism can happen if a diver runs out of air and holds their breath while coming up to the surface.

This can cause damage to the lungs, called pulmonary barotrauma, which allows air bubbles to enter the blood.

Air embolism can also happen when a diver surfaces too quickly. This is commonly known as the bends or decompression sickness.

These are explained in more detail below.

Pulmonary barotrauma

Pulmonary barotrauma is injury to the lungs caused by a change in pressure.

It happens when divers run out of air and, in a panic, hold their breath while rapidly swimming to the surface. As they come up and the pressure around them decreases, the air in their lungs expands. The expanding air causes the lungs to overinflate, which can rupture the alveoli (tiny air sacs in the lungs). Air can escape from the lungs and enter the blood vessels, which can cause an air embolism.

Air embolism can happen in as little as one metre of water, if the diver is breathing compressed air and holds their breath while rapidly surfacing.

Decompression sickness

Decompression sickness happens when nitrogen that is dissolved in the blood under high pressure forms bubbles when a diver comes up to the surface.

When deep underwater, divers breathe compressed air that contains nitrogen gas. This accumulates in the diver's blood and tissues. When the diver comes up and sea pressure decreases, the nitrogen forms bubbles in the tissues and blood as it cannot be breathed out immediately. These bubbles may lead to an air embolism.

The following factors increase the risk of decompression sickness:

• some heart defects
• cold water
• dehydration
• fatigue (tiredness)
• increased depth of water (due to higher pressure)
• increased time spent in deep water
• obesity
• older age
• coming up to the surface rapidly
• repeated dives on the same day
• flying immediately after diving

Other causes

Air embolism from other causes is very rare. It can occasionally occur in the following situations:

• surgery to the blood vessels or large blood transfusions, if a large quantity of air is mistakenly injected into the vessels (although doctors are trained to remove excess air from a syringe before giving injections)
• operations including caesarean sections or open-heart surgery, if air becomes trapped inside the body,
• an injury in which the chest is crushed, such as in a car crash
• removal of a catheter (a thin, flexible tube that is inserted into the body)
• oral sex during pregnancy (there have been a few reported cases of an air embolism occurring when air blown into the vagina has got into the enlarged blood vessels surrounding the pregnant woman's vagina)

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.

The symptoms, such as dizziness and blurred vision, usually appear a few minutes after surfacing (see Air embolism - symptoms for more information).

A physical examination and tests, such as chest X-rays, may be carried out by a doctor to check that the symptoms are not caused by another condition.

If a scuba diver loses consciousness within 10 minutes of surfacing, they probably have an air embolism and should be treated immediately (see Air embolism - treatment for more information).

Monitoring patients during surgery

There are several ways to monitor a person during surgery if they are thought to be at risk of developing an air embolism.

Transesophageal echocardiography

A tiny scanner on the end of a thin tube is inserted into the body, through the mouth and down the airway, to monitor the heart with ultrasound. This can detect relatively small air bubbles. However, it is invasive (medical instruments enter the body) and cannot locate where the bubble is in the body.

Doppler ultrasound

An ultrasound scanner is placed over the right side of the heart to measure the speed of bloodflow and changes in blood density. It is quite sensitive and is commonly used during surgical procedures to the nervous system.

However, it cannot determine the size of the embolus or distinguish between life-threatening and minor air bubbles. It can sometimes be difficult to place the equipment on the person, especially if they are obese.

Pulmonary artery catheter

A tiny tube is inserted into the artery connecting the heart to the lungs and blood pressure is monitored. A change in blood pressure shows that an air embolism may be present.

However, a change in blood pressure could have another cause, so this is not a routine method of monitoring.

Glossary

Catheter

A catheter is a thin, hollow tube, usually made of rubber, that is placed into the bladder to inject or remove fluid.

Pain

Pain is an unpleasant physical or emotional feeling and your body's way of warning you it has been damaged.

Artery

Arteries are blood vessels that carry blood from the heart to the rest of the body.

Ultrasound

Ultrasound scans produce pictures of inside the body using soundwaves.

Blood

Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

Embolism

An embolism is the sudden blockage of a blood vessel, usually by a blood clot or air bubble.

Heart

The heart is a muscular organ that pumps blood around the body.

Obese

Obesity is when a person has an abnormally high amount of body fat.

Lungs

Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.

If a diver has decompression sickness or lung damage and develops an air embolism, the only effective treatment is immediate recompression 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 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.

Patients in surgery

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

• Prevent more air from entering the body by sealing the open blood vessels.
• Reduce the amount of air already in the body using a hyperbaric oxygen chamber.
• Support the heart and lungs. A fall in blood pressure can be prevented by introducing fluids. Drugs, such as adrenaline, will keep the heart functioning. If possible, the site of the operation should be positioned lower than the level of the heart, by repositioning the person or tilting the operating table.
• Treat other symptoms. For example, if the person has an air embolism in the arteries to the brain, it may cause seizures, which are treated using drugs called barbiturates.

Glossary

Brain

The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.

Arteries

Arteries are blood vessels that carry blood from the heart to the rest of the body.

Vein

Veins are blood vessels that carry blood back to the heart from the rest of the body.

Blood

Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

Embolism

An embolism is the sudden blockage of a blood vessel, usually by a blood clot or air bubble.

Heart

The heart is a muscular organ that pumps blood around the body.

Blood vessels

Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessel are arteries, veins and capillaries.

Oxygen

Oxygen is an odourless, colourless gas that makes up about 20% of the air we breathe.

Lungs

Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.

Divers should be properly trained and aware of the dangers of decompression sickness and pulmonary barotrauma (lung damage caused by high pressure).

Training should include how to go down into the water and surface safely.

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 that 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 (see Air embolism - causes for more information). 
• After diving, wait for 12 to 24 hours before flying or going to a higher altitude.

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 that are inserted into the body should be removed using a technique that minimises the possibility of air embolism.

Glossary

Blood vessels

Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessel are veins, arteries and capillaries.

Embolisms

An embolism is the sudden blockage of a blood vessel, usually by a blood clot or air bubble.