(See also Overview of Diving Injuries Overview of Diving Injuries More than 1000 diving-related injuries occur annually in the US; > 10% are fatal. Similar injuries can befall workers in tunnels or caissons (watertight retaining structures used for construction)... read more .)
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 Decompression Sickness Decompression sickness occurs when rapid pressure reduction (eg, during ascent from a dive, exit from a caisson or hyperbaric chamber, or ascent to altitude) causes gas previously dissolved... read more
Via migration from the venous circulation (venous gas embolism) either via a right-to-left shunt (patent foramen ovale Neonatal Cardiovascular Function The transition from life in utero to life outside the womb involves multiple changes in physiology and function. See also Perinatal Problems. (See also Liver Structure and Function and Neonatal... read more , atrial septal defect Atrial Septal Defect (ASD) An atrial septal defect (ASD) is an opening in the interatrial septum, causing a left-to-right shunt and volume overload of the right atrium and right ventricle. Children are rarely symptomatic... read more ) or by overwhelming the filtering capacity of the lungs
Even an otherwise asymptomatic venous gas embolism Air embolism Nonthrombotic sources of pulmonary embolism include air, fat, amniotic fluid, infected material, foreign bodies, and tumors. Pulmonary embolism (PE) can arise from nonthrombotic sources. PE... read more can cause serious manifestations (eg, stroke Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more 
) 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 Symptoms and Signs .
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).
Symptoms and Signs
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 Pulmonary Barotrauma Barotrauma is tissue injury caused by a pressure-related change in body compartment gas volume. Factors increasing risk of pulmonary barotrauma include certain behaviors (eg, rapid ascent, breath-holding... read more or type II decompression sickness Symptoms and Signs may also be present.
Other symptoms may result from arterial gas embolism in any of the following:
Coronary arteries (eg, arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more
, myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more 
, cardiac arrest Cardiac Arrest Cardiac arrest is the cessation of cardiac mechanical activity resulting in the absence of circulating blood flow. Cardiac arrest stops blood from flowing to vital organs, depriving them of... read more )Skin (eg, cyanotic marbling of the skin, focal pallor of the tongue)
Kidneys (eg, hematuria Isolated Hematuria Hematuria is red blood cells (RBCs) in urine, specifically > 3 RBCs per high-power field on urine sediment examination. Urine may be red, bloody, or cola-colored (gross hematuria with oxidation... read more , proteinuria Proteinuria Proteinuria is protein, usually albumin, in urine. High concentrations of protein cause frothy or sudsy urine. In many renal disorders, proteinuria occurs with other urinary abnormalities (eg... read more , renal failure Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more )
Diagnosis
Clinical evaluation
Sometimes 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)
Sometimes decompression sickness Decompression Sickness Decompression sickness occurs when rapid pressure reduction (eg, during ascent from a dive, exit from a caisson or hyperbaric chamber, or ascent to altitude) causes gas previously dissolved... read more can cause similar symptoms and signs (for a comparison of features, see table Comparison of Gas Embolism and Decompression Sickness Comparison of Gas Embolism and Decompression Sickness 
).
Treatment
Immediate 100% oxygen
Recompression therapy
Divers thought to have arterial gas embolism should be recompressed promptly (1 Treatment reference 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... read more ). Transport to a recompression chamber Recompression Therapy Recompression therapy is administration of 100% oxygen for several hours in a sealed chamber pressurized to > 1 atmosphere, gradually lowered to atmospheric pressure. In divers, this therapy... read more takes precedence over nonessential procedures. Transport by air may be justified if it saves significant time, but exposure to reduced pressure at altitude must be minimized.
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; to help prevent aspiration, if tracheal intubation is not feasible, unconscious patients with impaired airway reflexes should be kept in the lateral decubitus position. 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 is no longer recommended.
Treatment reference
1. Moon RE: Hyperbaric treatment of air or gas embolism: current recommendations. Undersea Hyperb Med, 46(5):673-683, 2019. PMID: 31683367.
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
