Air Embolism

Undissolved intravascular air can occur as an arterial gas embolus (AGE) or venous gas embolus (VGE). Volumes of 100 to 300 ml are considered fatal; in canine models, 0.5 to 1.0 ml/kg causes 40% mortality.

AGE can occur from rapid ascent during dives (a form of "the bends"), intrathoracic trauma, hydrogen peroxide ingestion, other pressurized gas inhalation, or a VGE that crosses from right to left through a foramen ovale or ventricular septal defect. AGEs travel to cerebral arteries (most common), coronary arteries, or spinal arteries, causing strokes, ischemia, infarction, dysrhythmias, or paralysis.

VGE can occur as a complication of central venous catheterization, penetrating and blunt chest trauma, high-pressure mechanical ventilation after chest trauma, thoracocentesis, hemodialysis, and a variety of surgical procedures. It can cause immediate hypoxia, hemodynamic collapse (thought to be from obstruction of the right pulmonary outflow tract), and death. Venous gas bubbles are commonly observed after diving and are most often asymptomatic. (Divers are also at risk for pneumothorax if ascent is made without exhalation of expanding lung gases.) Lethality of air emboli depends on rate and volume of embolized air and position of the patient at the time. Higher rates and volumes and sitting position increase mortality.

Causes

Air embolism sometimes occurs to divers who run out of air and hold their breath while coming to the surface. This is commonly known as 'the bends'.

Divers often breathe high-pressure air at depth and surface without allowing the expanding air to escape freely. The air in the lungs expands and a bubble of nitrogen enters the veins that carry blood back to the heart. The air bubbles can prevent the flow of blood to the brain and other vital organs and can also cause clots to form in blood vessels.

Air embolism can very occasionally occur during surgery to the arteries, if a large quantity of air is mistakenly injected into them. There is a similar risk during large blood transfusions, Caesarean sections and open- heart surgery. But precautions are always taken to prevent this from happening. Eg, before injections are given, any excess air is removed from the syringe.

Embolism can sometimes result from an injury in which the chest is crushed. There have been a few reported cases of an air embolism occurring as a result of oral sex during pregnancy.

Symptoms

AGE

Neurologic symptoms often overshadow cardiopulmonary symptoms; in sport divers, symptoms most frequently occur within 10 minutes of surfacing ++++, but may be delayed.

• Loss of consciousness +++
• Dyspnea +++
• Limb paralysis or numbness +++
• Severe headache ++
• Aphasia or dysarthria ++
• Hemoptysis ++
• Seizures

VGE

• Breathlessness, dyspnea
• Chest pain
• Sense of impending death

Signs

AGE

Cerebral embolism:

• Neurologic signs: altered mental status, focal deficits, seizure.
• Pulmonary signs: crepitus, unequal breath sounds (pneumothorax)

Coronary embolism:

• Dysrhythmias

VGE

Depends on the rate of embolus formation. All signs are nonspecific, especially in multiple trauma scenarios, which makes diagnosis difficult.

• Sudden gasp, wheeze
• Rapid, shallow respirations followed by apneic period
• Tachycardia
• Hypotension, cardiovascular collapse if severe
• Loss of consciousness; altered mental status
• Unexplained decrease in PETC02 and O2 saturation
• The only specific sign, a "mill-wheel" murmur, is an uncommon and late sign, present only after cardiovascular deterioration has begun ++++

Treatment

Oxygen first aid treatment is very useful for suspected gas embolism casualties or divers who have made fast ascents. Most fully closed-circuit rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators.

Emergency Department Care: Once VAE is suspected, any central line procedure in progress should be terminated immediately.

• Administer full persent oxygen and intubate for significant respiratory distress. Oxygen may reduce bubble size by increasing the gradient for nitrogen to move out.
• Maintain systemic arterial pressure with fluid resuscitation and vasopressors/beta-adrenergic agents if necessary.