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:
Coronary arteries (eg, arrhythmias, myocardial infarction, cardiac arrest)
Skin (eg, cyanotic marbling of the skin, focal pallor of the tongue)
Kidneys (eg, hematuria, proteinuria, renal failure)
Pearls & Pitfalls
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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.
Comparison of Gas Embolism and Decompression Sickness
Feature | Gas Embolism | Decompression Sickness |
|---|---|---|
Symptoms and signs | Common: Unconsciousness, often with seizures (any diver who loses consciousness shortly after surfacing should be assumed to have arterial gas embolism and should be recompressed promptly) Less common: Milder cerebral manifestations, signs of pulmonary barotrauma (eg, mediastinal or subcutaneous emphysema, pneumothorax) | Extremely variable—the bends (pain, most often in or near a joint), neurologic manifestations of almost any type or degree, and the chokes (respiratory distress followed by circulatory collapse—an extreme emergency), occurring alone or with other symptoms |
Onset | Sudden, usually during or within a few minutes after surfacing | Usual: Gradual or sudden, with symptoms developing ≥ 1 hour after surfacing in about 50%; onset up to 24 hours after dives* of > 10 m (> 33 ft) or hyperbaric exposures of > 2 ATA Rare: Symptoms developing > 24 hours after surfacing is rare although altitude exposure (eg, commercial aircraft flight) can cause delayed onset |
Proximate cause | Usual: Breath holding or airway obstruction during ascent (even from a meter [a few feet] of depth, particularly when ascent is rapid); air trapped in the lungs expands during ascent and causes lung tissue injury Occasional: Severe decompression sickness resulting in arterial bubbles or intrapulmonary gas trapping due to preexisting lung disease (eg, bullae, interstitial lung disease) | Usual: Diving or hyperbaric exposure, especially beyond no-stop limits Occasional: Diving or hyperbaric exposure to shallow depths (12 m [40 ft] or shallower); low-pressure exposure (eg, flying after diving) |
Mechanism | Usual: Overinflation of lungs causing entry of free gas into pulmonary vessels followed by embolization of cerebral vessels Occasional: Coronary, renal, or cutaneous circulatory obstruction by free gas from any source | Formation of bubbles from excess dissolved gas in blood or tissue when external pressure decreases |
Emergency treatment | Essential emergency care as needed (eg, airway patency, hemostasis, CPR or mechanical ventilation) Prompt transport to nearest recompression chamber Horizontal position if needed to maintain blood pressure Unconscious patients with impaired airway reflexes should be kept in the lateral decubitus position to help prevent aspiration, if tracheal intubation is not feasible 100% oxygen by close-fitting mask Fluids orally if patient is conscious; otherwise, IV Arterial gas embolism after only a short, shallow dive may not require aggressive fluid administration | Essential emergency care as needed (eg, airway patency, CPR or mechanical ventilation) Prompt transport to nearest recompression chamber Horizontal position if needed to maintain blood pressure Unconscious patients with impaired airway reflexes should be kept in the lateral decubitus position to help prevent aspiration, if tracheal intubation is not feasible 100% oxygen by close-fitting mask Fluids orally if patient is conscious; otherwise, IV |
* Repeat dives are frequently involved. | ||
ATA = atmospheres absolute; CPR = cardiopulmonary resuscitation. | ||
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
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Treatment references
1. Moon RE: Hyperbaric treatment of air or gas embolism: Current recommendations. Undersea Hyperb Med 46(5):673-683, 2019. PMID: 31683367.
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.
Divers Alert Network: 24-hour emergency hotline, 919-684-9111
Duke Dive Medicine: Physician-to-physician consultation, 919-684-8111
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
