Arterial Air Embolism

Arterial air embolism is air in the systemic arterial circulation, causing organ ischaemia, most often cerebral and coronary. It arises from the pulmonary veins (barotrauma, lung surgery), cardiac surgery or catheter lines, or from paradoxical passage of venous air.

Epidemiology. It is rare but serious, with cerebral injury in most cases. Causes include cardiopulmonary bypass and cardiac surgery, lung biopsy and surgery, positive pressure ventilation with barotrauma, haemodialysis, intra-arterial line flush, central line complications and scuba diving. Small volumes (0.5 mL in the left coronary artery, 2 mL in the cerebral circulation) can be fatal.

Risk factors. Patent foramen ovale, intracardiac shunt, open cardiac chambers, high airway pressure, lung disease, air in arterial lines, and diving.

Pathophysiology.

Air bubbles block small arteries, causing ischaemia, endothelial injury, inflammation, platelet activation and oedema. Bubbles in cerebral arteries produce focal deficits, and coronary air produces ischaemia and arrhythmia.

Sudden neurological deficit (loss of consciousness, seizures, focal weakness, visual loss, confusion), ST changes, arrhythmia, hypotension, cardiac arrest, livedo reticularis or skin marbling, and air in retinal vessels.

Red flags.

• New focal deficit or seizure after surgery or line manipulation.
• ST elevation or ventricular arrhythmia.
• Failure to wake after anaesthesia.

Clinical, with CT head (air bubbles; may be missed after 2 hours) or MRI (diffusion restriction). Transoesophageal echocardiography for intracardiac air or shunt. ECG directed by symptoms. Do not delay treatment for imaging.

Differential diagnosis.

• Thromboembolic stroke.
• Intracranial haemorrhage.
• Seizure.
• Hypoglycaemia.
• Hypoxic brain injury.
• Myocardial infarction.

Stop the air source, clamp lines, give 100% oxygen by tight fitting mask or ventilator (to speed nitrogen washout), and lay the patient flat (supine; avoid Trendelenburg for cerebral air, which raises cerebral oedema).

Support circulation, treat seizures, and keep mean arterial pressure at 65 mmHg or more with normothermia and normoglycaemia (4 to 10 mmol/L).

• Lorazepam: 4 mg IV (children 0.1 mg/kg) for seizures, repeated once after 10 minutes; maximum 8 mg; monitor respiration.
• Noradrenaline: 0.05 to 0.5 microgram/kg/min to maintain perfusion; maximum 1 microgram/kg/min.

Hyperbaric oxygen at 2.8 atmospheres absolute for 4 to 6 hours initially (then further sessions by response) is the definitive treatment and works best within 6 hours, with benefit even if delayed up to 24 hours or more. Transfer to a hyperbaric facility without delay (in an unpressurised aircraft below 300 m or pressurised to sea level).

In cardiac surgery with air in the aortic root, consider retrograde cerebral perfusion and hypothermia. Aspirate coronary air by increasing perfusion pressure.

Monitoring. Neurological observation, ECG directed by symptoms, blood gases, and glucose.

Referral and escalation. Hyperbaric medicine, critical care, neurology and cardiothoracic surgery.