Air Embolism (Gas Embolism)

How an air embolism happens

Venous air embolism

Air enters a vein, usually through a medical device or wound, especially when the vein sits above the level of the heart or when breathing in creates negative pressure. Bubbles travel to the right side of the heart and the lungs. Small amounts are filtered by the lungs without harm. Larger amounts can block blood flow out of the heart ("air lock"), causing low blood pressure, low oxygen and cardiac arrest.

The lethal volume in adults is thought to be roughly 200 to 300 ml, or about 3 to 5 ml per kg, especially if delivered quickly. Small bubbles seen in a peripheral IV line are usually harmless in adults, although care is still taken to remove them.

Arterial gas embolism

Bubbles in the arteries can block blood supply to the brain or heart, so even small amounts can cause stroke or heart attack symptoms. This happens:

• in divers whose lungs over-expand and tear while ascending, letting air into the lung veins (pulmonary barotrauma)
• when venous bubbles cross into the arteries through a hole in the heart, such as a patent foramen ovale, present in about a quarter of adults
• during heart, lung or brain surgery and some lung biopsies

Causes

Diving

The most common non-medical cause. Breathing compressed air at depth and then ascending rapidly or holding the breath lets expanding air rupture lung tissue. Even a shallow ascent from about 1 to 2 meters (4 to 6 feet) with a held breath can cause it. Symptoms usually start within 10 minutes of surfacing.

Medical procedures

• Central venous catheters: insertion, disconnection or removal, especially if the patient is sitting up or breathes in deeply.
• Surgery: brain surgery done sitting up, spinal, heart, hip replacement, laparoscopic surgery and cesarean delivery.
• Hemodialysis, IV contrast injectors and pressurized infusions.
• Lung biopsies and mechanical ventilation with high pressures.

Injuries

Chest trauma, penetrating neck wounds and blast injuries.

Other

Rarely, air introduced into the vagina during pregnancy (for example during oral sex) or through certain cosmetic or alternative procedures.

Symptoms

In divers, symptoms may come with signs of lung injury: coughing up blood, chest pain, pneumothorax or air under the skin of the neck.

How it is diagnosed

Diagnosis is mainly based on the timing: sudden symptoms during a procedure or soon after surfacing from a dive. Treatment should not be delayed for tests. Supporting tests include:

• echocardiography (shows bubbles in the heart)
• CT scans of the brain or chest
• monitoring of exhaled carbon dioxide during surgery, which drops suddenly
• chest X-ray for lung injury in divers

Treatment

Immediate steps

1. Stop further air entry: clamp or close the line, flood the surgical field with saline, cover a wound.
2. 100% oxygen by mask, which helps shrink bubbles and improves oxygen delivery.
3. Positioning: for venous air embolism, lying on the left side with the head slightly down may help keep air trapped in the right heart away from the lung outflow. For arterial and diving embolism, keep the person lying flat; head-down positions are no longer recommended because they can increase brain swelling.
4. Life support: fluids, medicines to support blood pressure, and CPR if needed. Air can sometimes be withdrawn through a central line positioned in the heart.

Hyperbaric oxygen therapy

Breathing pure oxygen in a pressurized chamber shrinks bubbles and speeds their removal. It is the main treatment for arterial gas embolism, especially in divers and in people with neurological symptoms, and works best when started quickly. Divers Alert Network and similar organizations help locate chambers.

Complications and outlook

Outcomes depend on the amount of gas, the organs affected and the speed of treatment. Many people recover fully, particularly with prompt hyperbaric treatment. Others are left with lasting neurological effects, and large emboli can be fatal.

Prevention

For divers

• Never hold your breath while ascending; breathe normally.
• Ascend slowly, follow safety stops and dive tables or computers.
• Do not dive with a cold, chest infection or uncontrolled asthma.
• After lung barotrauma or an arterial gas embolism, get a specialist dive medicine assessment before diving again.

In healthcare

• Lie patients flat or head-down during central line insertion and removal.
• Ask patients to hold their breath or hum during line removal, then apply an airtight dressing.
• Prime and check IV lines and use air-detection on pumps.

Frequently asked questions

What are the symptoms of an air embolism?

Symptoms appear suddenly and include breathlessness, chest pain, coughing, low blood pressure, confusion, weakness or numbness, seizures and loss of consciousness. In divers, these usually start within 10 minutes of surfacing. Any of these after a dive or medical procedure needs emergency care.

How much air in an IV causes an embolism?

Small bubbles in a standard IV line are generally harmless in adults because the lungs filter them. Serious venous air embolism is thought to need a much larger amount, often estimated at 200 to 300 ml in adults, entering rapidly. Arterial air is dangerous in much smaller amounts.

Can you survive an air embolism?

Yes. Many people survive and recover fully, especially with fast treatment using 100% oxygen and hyperbaric oxygen therapy. The outcome depends on how much air entered, where it went, and how quickly treatment started.

What causes an air embolism in divers?

Holding the breath or ascending too quickly lets air in the lungs expand and tear lung tissue, pushing bubbles into the blood vessels that lead to the heart and brain. This is called pulmonary barotrauma with arterial gas embolism and can occur even in shallow water.

How is air embolism treated?

Treatment includes stopping further air entry, giving 100% oxygen, careful positioning, supporting breathing and blood pressure, and hyperbaric oxygen therapy in a pressurized chamber, which shrinks the bubbles. CPR is started if the heart stops.