Arterial Gas Embolism

(Air Embolism)

ByRichard E. Moon, MD, Duke University Medical Center
Reviewed/Revised Apr 2023
View Patient Education

Arterial gas embolism is a potentially catastrophic event that occurs when gas bubbles enter or form in the arterial vasculature and occlude blood flow, causing organ ischemia. Arterial gas embolism can cause central nervous system (CNS) ischemia with rapid loss of consciousness, other CNS manifestations, or both; it also may affect other organs. Diagnosis is clinical and does not require confirmation by imaging. Treatment is 100% oxygen and recompression as soon as possible.

(See also Overview of Diving Injuries.)

Gas emboli may enter the arterial circulation in any of the following ways:

  • From ruptured alveoli after lung barotrauma

  • From within the arterial circulation itself in severe decompression sickness

  • Via migration from the venous circulation (venous gas embolism) either via a right-to-left shunt (patent foramen ovale, atrial septal defect) or by overwhelming the filtering capacity of the lungs

Even an otherwise asymptomatic venous gas embolism can cause serious manifestations (eg, stroke) in the presence of a right-to-left shunt. Venous gas embolism that does not enter the arterial circulation is less serious, although high levels of venous gas embolism can cause pulmonary edema, known as chokes.

Although cerebral embolism is considered the most serious manifestation, arterial gas embolism can cause significant ischemia in other organs (eg, spinal cord, heart, skin, kidneys, spleen, gastrointestinal tract).

Deep vein thrombosis and pulmonary embolism can complicate immobilization due to air embolism.

Symptoms and Signs of Arterial Gas Embolism

Symptoms occur within a few minutes of surfacing and may include altered mental status, hemiparesis, focal motor or sensory deficits, seizures, loss of consciousness, apnea, and shock; death may follow. Signs of pulmonary barotrauma or type II decompression sickness may also be present.

Other symptoms may result from arterial gas embolism in any of the following:

Pearls & Pitfalls

  • Any diver who loses consciousness shortly after surfacing is most likely to have arterial gas embolism and should be treated with hyperbaric oxygen as quickly as possible.

Diagnosis of Arterial Gas Embolism

  • Clinical evaluation

  • Rarely, confirmation by imaging

Diagnosis is primarily clinical. A high level of suspicion is necessary when divers lose consciousness during or immediately after ascent. Confirming the diagnosis is difficult because air may be reabsorbed from the affected artery before testing. Also, imaging should be used only if the diagnosis is not clear, because imaging can delay treatment. However, imaging techniques that may support the diagnosis (each with limited sensitivity and thus should not be used to exclude the diagnosis) include the following:

  • Echocardiography (showing air in the cardiac chambers)

  • Chest CT (showing local lung injury or hemorrhage)

  • Head CT (showing intravascular gas and diffuse edema), although visible arterial gas is inconsistently present and its absence does not rule out arterial gas embolism

  • Abdominal CT (showing gas within mesenteric vessels or the portal vein)

Assessment should also include evaluation for other potential causes of loss of consciousness, including carbon monoxide poisoning due to contaminated breathing gas. Sometimes decompression sickness can cause similar symptoms and signs (for a comparison of features, see table Comparison of Gas Embolism and Decompression Sickness ).

Because decompression sickness or arterial gas embolism can be complicated by deep vein thrombosis and pulmonary thromboembolism, periodic ultrasonography of the leg veins should be considered.


Treatment of Arterial Gas Embolism

  • Immediate 100% oxygen

  • Recompression therapy

Divers thought to have arterial gas embolism should be recompressed as soon as possible (1, 2). Transport to a recompression chamber takes precedence over nonessential procedures.

Before transport, high-flow 100% oxygen enhances nitrogen washout by widening the nitrogen pressure gradient between the lungs and the circulation, thus accelerating reabsorption of the nitrogen-containing embolic bubbles. Hemodynamically unstable patients should remain in a supine position to facilitate maintenance of stable blood pressure and cardiac output.

Transport by air may be justified if it saves significant time. It had been previously recommended against to minimize exposure to reduced pressure at altitude due to the possibility of bubble volume expansion. However, if the patient has been breathing high-flow oxygen, air transport is usually well tolerated. In addition, air ambulances capable of maintaining sea-level cabin pressure may be available.

Unconscious patients with impaired airway reflexes should be kept in the lateral decubitus position to help prevent aspiration, if tracheal intubation is not feasible. Mechanical ventilation, vasopressors, and volume resuscitation are used as needed.

Routine placement of all patients in the left lateral decubitus position (Durant’s maneuver) or Trendelenburg position, which was previously thought to prevent cephalad migration of bubbles, is not effective and is no longer recommended.

Pearls & Pitfalls

  • Place unconscious patients with impaired airway reflexes in the lateral decubitus position until the airway can be protected with an endotracheal tube, after which the patient can be placed supine to facilitate care. Left lateral decubitus position (Durant’s maneuver) or Trendelenburg position are no longer routinely recommended.

Treatment references

  1. 1. Moon RE: Hyperbaric treatment of air or gas embolism: Current recommendations. Undersea Hyperb Med 46(5):673-683, 2019. PMID: 31683367.

  2. 2. Mitchell SJ, Bennett MH, Moon RE: Decompression sickness and arterial gas embolism. N Engl J Med 386(13):1254-1264, 2022. doi: 10.1056/NEJMra2116554

Key Points

  • Strongly consider arterial gas embolism if patients have neurologic symptoms within minutes after surfacing or have manifestations of ischemia in another organ.

  • Do not exclude arterial gas embolism based on negative imaging results.

  • Routine imaging to look for intravascular air is not indicated.

  • Start high-flow 100% oxygen and initiate transport to a recompression chamber if gas embolism is suspected.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  1. Divers Alert Network: 24-hour emergency hotline, 919-684-9111

  2. Duke Dive Medicine: Physician-to-physician consultation, 919-684-8111

  3. Undersea and Hyperbaric Medical Society: Scientific and medical information pertaining to undersea and hyperbaric medicine through its bimonthly, peer-reviewed journal, Undersea and Hyperbaric Medicine, and other resources

Test your KnowledgeTake a Quiz!
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID