Air Embolism

Air embolism here means venous air embolism: air enters the systemic veins and travels to the right heart and pulmonary circulation. It occurs when a vein open to the atmosphere sits above the level of the heart, so that negative intrathoracic pressure on inspiration draws air in. Entrainment of 3 to 5 mL/kg of air over a short time (about 200 to 300 mL in an adult) is potentially fatal. Smaller volumes cause symptoms.

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• Central venous catheter insertion, use, disconnection and removal (the commonest cause)
• Neurosurgery in the sitting position, and spinal and head and neck surgery
• Laparoscopy and hysteroscopy with gas insufflation, cesarean section, liver resection and orthopedic surgery with pressurized irrigation
• Haemodialysis and cardiopulmonary bypass circuits, and pressurized IV infusion without air filters
• Chest trauma, lung biopsy and vaginal insufflation in pregnancy

Mechanism: air collects in the right ventricle as a froth that obstructs outflow (an air lock), raising pulmonary artery pressure and dead space, and causing right ventricular failure, falling cardiac output, hypoxemia and a sharp fall in end-tidal carbon dioxide. Microbubbles in the pulmonary capillaries release inflammatory mediators and cause noncardiogenic pulmonary edema.

In 20 to 30% of adults a patent foramen ovale allows bubbles to cross to the arterial side (paradoxical embolism), which causes stroke and myocardial ischemia. Mortality ranges from 20 to 50% in large events. Complications: cardiac arrest, right heart failure, pulmonary edema, stroke and seizures.

• In an anesthetized patient: sudden fall in end-tidal carbon dioxide, hypotension, tachycardia, arrhythmia, oxygen desaturation and, with large volumes, cardiovascular collapse
• In an awake patient: sudden dyspnea, chest pain, cough, gasp reflex, anxiety, light-headedness and a feeling of impending doom
• A "mill-wheel" churning murmur over the precordium (a late sign)
• Neurological signs from paradoxical embolism: confusion, hemiparesis, seizures and visual loss
• Red flags: collapse during a central line procedure or after a line disconnection, and sudden desaturation during surgery with the operative site above the heart

1. Clinical diagnosis from the event, since delay is dangerous and treatment should start on suspicion.
2. Monitoring findings: an abrupt drop in end-tidal carbon dioxide of 2 mmHg or more, falling oxygen saturation, rising pulmonary artery pressure, and hypotension.
3. Precordial Doppler ultrasound is the most sensitive monitor (it detects 0.05 mL/kg) and is used in high-risk neurosurgery. Transesophageal echocardiography shows bubbles in the right heart and a patent foramen ovale, and is the most sensitive imaging test.
4. Aspiration of air through a central line whose tip lies in the right atrium confirms the diagnosis.
5. ECG: right heart strain, ST changes and arrhythmia. Chest radiograph or CT: gas in the right ventricle or pulmonary artery, usually normal.
6. Arterial blood gas: hypoxemia and respiratory acidosis.

Differentials: pulmonary thromboembolism, myocardial infarction, anaphylaxis, tension pneumothorax, hypovolemia and tamponade.

1. Stop further entry of air at once: flood the surgical field with saline, cover it with wet swabs, lower the operative site below the level of the heart, clamp or occlude any open line, and apply pressure over the jugular veins when appropriate.
2. Oxygen: 100% oxygen. Stop nitrous oxide at once, since it expands bubbles. Intubate and ventilate for respiratory failure.
3. Positioning: left lateral decubitus with the head down, which may keep air in the right atrium away from the outflow tract. Return to supine for resuscitation and compressions.
4. Aspirate air from the right atrium through a central line (a multi-orifice catheter positioned at the junction of the superior vena cava and the right atrium) with a syringe.
5. Circulatory support: IV 0.9% saline 500 mL bolus to raise right-sided pressure and push air through, and norepinephrine 0.05 to 0.5 micrograms/kg/min IV, or epinephrine 0.05 to 0.5 micrograms/kg/min IV, for hypotension.
6. Cardiac arrest: chest compressions, which can break the air lock and drive bubbles into the pulmonary circulation, plus standard resuscitation, with open cardiac massage or thoracotomy with direct needle aspiration of the ventricle in refractory cases.
7. Hyperbaric oxygen for paradoxical embolism with neurological deficit or persistent cardiovascular compromise: pressurization to 2.8 atmospheres absolute with 100% oxygen in the first treatment, repeated daily until no further improvement (the benefit is greatest within 6 hours but extends to 24 hours).
8. Seizures: lorazepam 4 mg IV (children 0.1 mg/kg), repeated once.

Prevention: place the patient head-down for central line insertion and removal, ask the awake patient to hum or perform a Valsalva maneuver, clamp lines before disconnection, use luer-lock connections and air filters, prime all lines, and cover the exit site of a removed catheter with an airtight occlusive dressing for 24 to 72 hours. Follow-up at 1 week with cardiology review when a patent foramen ovale is found.