Venous Air Embolism: Pathophysiology, Volumes, and Clinical Effects

A venous air embolism (VAE) occurs when air enters the systemic venous circulation and travels to the right heart and pulmonary vasculature. Although uncommon, VAE is a potentially catastrophic perioperative complication that can rapidly lead to cardiovascular collapse if not promptly recognized and treated.

Critical Volumes of Air

• Approximately 5 mL/kg of venous air is considered sufficient to cause significant injury, including cardiovascular shock or cardiac arrest

• Serious complications have been reported with as little as 20 mL of air, particularly when air enters rapidly

The rate of air entry is often more important than the absolute volume.

Pathophysiology

Rapid entry of air into the venous system places an acute strain on the right ventricle. Air bubbles obstruct pulmonary blood flow, leading to a rise in pulmonary artery pressure and right ventricular outflow obstruction.

As pulmonary circulation becomes compromised:

• Pulmonary venous return to the left heart decreases

• Left ventricular preload falls

• Cardiac output drops

• Systemic hypotension and cardiovascular collapse may occur

Large air emboli can act as an “air lock” within the right ventricle, preventing effective forward blood flow.

Cardiac Rhythm Disturbances

Venous air embolism commonly produces tachyarrhythmias, secondary to acute right heart strain and hypoxia. However, bradyarrhythmias may also occur, particularly as cardiac output falls and myocardial ischemia develops.

Progression may include:

• Hypotension

• Hypoxia

• Pulseless electrical activity

• Cardiac arrest

Clinical Relevance

VAE is most often associated with:

• Surgical fields above the level of the heart

• Venous access under negative pressure

• Inadequate line priming or disconnection

Prompt recognition and immediate management are critical to preventing irreversible injury.

Board and Exam Pearls

• 5 mL/kg of air can be fatal

• 20 mL may cause serious complications

• Primary problem is right ventricular outflow obstruction

• Leads to decreased LV preload and cardiac output

• Tachyarrhythmias are common, but bradyarrhythmias can occur

Conclusion

Venous air embolism is a rare but life-threatening event characterized by acute right heart failure and impaired pulmonary circulation. Awareness of risk factors, rapid diagnosis, and immediate intervention are essential for preventing systemic cardiovascular collapse.