What are the causes of air embolism?

Causes of Air Embolism

Air embolism is caused primarily by the entrainment of air or exogenously delivered gas from the operative field or other environmental communication into the venous or arterial vasculature, producing potentially life-threatening systemic effects. 1

Common Causes of Air Embolism

Iatrogenic Causes

• Central venous catheter procedures: Most common iatrogenic cause, occurring during insertion, manipulation, or removal of central venous catheters and hemodialysis catheters 1
• Surgical procedures: Particularly neurosurgical procedures performed in the sitting position and other surgeries with exposure of venous sinuses 1
• Interventional procedures: Including lung biopsy, arterial catheterization, and endovascular procedures 2
• Pressurized venous infusions: Improper administration of IV fluids under pressure 2

Traumatic Causes

• Penetrating chest trauma: Creating direct communication between airways and pulmonary vessels 3
• Blunt chest trauma: Causing tears in pulmonary vessels with air entry 3

Other Medical Causes

• Mechanical ventilation: Particularly with high pressures in patients with lung injury 1
• Diving and aviation: Related to pressure changes causing gas expansion 3
• Obstetric procedures: During cesarean delivery or other obstetric interventions 1

Specific Types of Air Embolism

Venous Air Embolism

• Occurs when air enters the venous circulation and travels to the right heart and pulmonary circulation 1
• Most commonly associated with central venous catheter manipulation 1
• The lethal volume in humans is estimated between 200-300 ml or 3-5 ml/kg injected at a rate of 100 ml/s 1

Arterial Air Embolism

• Results from air entering the arterial circulation directly or through right-to-left cardiac shunts 2
• Can occur during lung biopsy, arterial catheterization, or cardiopulmonary bypass 2
• Even small volumes can cause significant neurological or cardiac damage 2

Pathophysiology and Effects

• Primary mechanism: Obstruction of the right ventricular pulmonary outflow tract or pulmonary arterioles by air bubbles and fibrin clots 1
• Hemodynamic effects: Cardiovascular dysfunction and failure due to obstruction of blood flow 1
• Pulmonary effects: Increased pulmonary artery pressures, ventilation-perfusion mismatch, and hypoxemia 3
• Systemic effects: When air crosses to systemic circulation (through patent foramen ovale or pulmonary capillaries), it can cause cerebral or coronary ischemia 1

Risk Factors

• Patient positioning: Procedures performed with the surgical site above the level of the heart increase risk 3
• Hypovolemia: Decreases venous pressure, increasing risk of air entrainment 3
• Presence of right-to-left shunts: Increases risk of paradoxical embolism 1
• Deep inspiration during catheter insertion or removal: Creates negative intrathoracic pressure that can draw air in 1

Prevention Strategies

• Proper positioning: Place patients in Trendelenburg position during central line insertion and removal 1
• Hydration: Ensure adequate volume status before procedures 3
• Technique: Use meticulous technique during catheter insertion and removal 1
• Monitoring: Use ECG monitoring during upper body CVC insertions 1
• Equipment: Secure connections and use Luer-lock devices 1
• Education: Ensure proper training for all practitioners performing high-risk procedures 4

Clinical Pearls and Pitfalls

• The severity of air embolism is directly related to the volume and rate of air entrainment 1
• Air embolism can occur at any time from catheter insertion to removal 1
• Presentation ranges from subtle neurological, respiratory, or cardiovascular signs to shock, loss of consciousness, and cardiac arrest 1
• Delayed presentation can occur, so continued monitoring after high-risk procedures is essential 1
• The diagnosis is often missed because symptoms can mimic other conditions 2