Air Embolism

Definition

• Venous Air Embolism (VAE) - air enters the venous circulation and affects the right heart/pulmonary vasculature
• Arterial (Systemic) Air Embolism (AAE) - air enters the left side of the circulation and reaches systemic organs (brain, heart)

Causes / Portals of Entry

Mechanism (Pathophysiology)

Venous Air Embolism

1. Airlock effect: A large bolus accumulates in the right ventricle or pulmonary outflow tract, forming foam that blocks right ventricular output → acute right heart failure, obstructive shock, and sudden death. Lethal volume is approximately 5 to 8 mL/kg.
2. Microvascular obstruction: Smaller bubbles lodge in pulmonary capillary beds → abrupt rise in pulmonary artery pressure → noncardiogenic pulmonary edema + reduced lung compliance → hypoxemia.
   • Platelet-fibrin aggregates form around bubbles → diffuse microthrombi → thrombocytopenia.
   • Bubbles can pass through pulmonary microvascular shunts → enter left-sided (arterial) circulation → paradoxical air embolism.

Arterial (Systemic) Air Embolism

• As little as 0.5 mL in the left anterior descending coronary artery can cause ventricular fibrillation.
• 2 mL injected into the cerebral circulation can be fatal.
• Entry occurs via bronchovenous fistulas (lung trauma) or paradoxical embolism through a patent foramen ovale.

Decompression Sickness (Special Form)

Symptoms

Cardiovascular

• Sudden drop in blood pressure / circulatory collapse
• Irregular heartbeat / cardiac arrest
• "Millwheel murmur" - a churning sound audible on cardiac auscultation (classic finding)

Respiratory

• Rapid, shallow breathing / dyspnea
• Continuous coughing
• Chest pain
• Coughing up blood (hemoptysis)
• Respiratory arrest

Neurological (if cerebral involvement)

• Headache, confusion, dizziness
• Vision changes
• Seizures
• Focal neurologic deficits / hemiparesis
• Loss of consciousness / coma
• Altered mental status

Systemic

• Sense of impending doom
• Paralysis in one area of the body

Key diagnostic clue: In trauma patients, cardiac arrest after intubation and initiation of positive-pressure ventilation + hemoptysis is highly suggestive. Focal neurological changes without head injury also raise suspicion. Confirmed at thoracotomy by needle aspiration of foamy air-blood mixture from the ventricle or visualization of air in coronary arteries.

Position (Durant's Maneuver + Trendelenburg)

Venous Air Embolism

• Left lateral decubitus: Encourages the air bubble to float to the right ventricular apex, away from the pulmonary outflow tract - relieves the "airlock" and prevents outflow obstruction.
• Trendelenburg (head-down): Encourages air to enter veins in the lower body; reduces air migrating to the cerebral circulation.
• Together these two positions allow air to be trapped in the right atrium and prevent further cardiovascular and cerebral migration.

Arterial Air Embolism

• Keep the patient in the flat supine position.
• The head-down position is avoided in arterial embolism because it may worsen cerebral edema.

Management

Immediate Steps (Stop the Source)

1. Clamp or disconnect the venous line / IV circuit immediately to stop further air entry
2. Stop blood pump (in dialysis setting)
3. Position the patient: Left lateral decubitus + Trendelenburg (VAE)

Cardiorespiratory Support

• 100% high-flow oxygen - accelerates bubble reabsorption (oxygen replaces nitrogen in bubbles, which are then absorbed faster)
• Secure airway: endotracheal intubation + mechanical ventilation if needed
• Hemodynamic support: maintain blood pressure and perfusion

Air Removal

• Aspiration through central venous catheter or right atrial catheter
• In extreme cases: needle aspiration of air from the right ventricle (needle introduced below the left costal margin, through the cardiac apex)
• Closed-chest cardiac massage if in arrest (helps break up air bubbles)

Definitive Therapy

• Hyperbaric oxygen therapy (HBO) - the treatment of choice for arterial gas embolism and severe venous events. Forces gas back into solution under high pressure; subsequent slow decompression allows gradual reabsorption without re-formation of bubbles. Also used for decompression sickness.

Management Flowchart (from Comprehensive Clinical Nephrology)

Summary Table

Prevention

• Air detection alarms on dialysis machines (never run dialysis without functioning alarm)
• Occlusive dressings over central line insertion sites; clamp lines during connection/disconnection
• Avoid glass IV bottles (create vacuum effect)
• Avoid sitting/head-elevated position in at-risk surgeries; use TEE monitoring in neurosurgery
• Aspirate and flush catheters with saline before connecting