Arterial Gas Embolism

Arterial gas embolism is the entry of gas bubbles into the arterial circulation, most often from pulmonary barotrauma during a breath hold ascent in diving. Cerebral embolism produces stroke like illness within minutes and is a medical emergency needing oxygen and recompression.

Mechanism in diving. Expansion of gas in the lungs on ascent, even from 1 to 2 metres when the breath is held or airways are obstructed, tears alveolar tissue and drives gas into pulmonary veins. Causes include breath holding, panic, asthma, cysts, blebs and air trapping.

Other causes. Iatrogenic (central venous lines, surgery, pressurised infusions, lung biopsy), ventilator barotrauma, and blast injury.

Severity. Loss of consciousness in diving is a sign of severe injury. Death follows cerebral or coronary embolism.

Timing. Symptoms usually start within 10 minutes of surfacing.

Pathophysiology.

Bubbles lodge in cerebral and coronary arteries and cause ischaemia, with endothelial injury, platelet and leucocyte activation and secondary oedema as the bubbles pass.

Bubbles shrink and dislodge, which explains early partial recovery and later relapse. Recompression reduces bubble volume and increases oxygen delivery.

• Sudden loss of consciousness, confusion, focal weakness, visual loss, speech disturbance, seizures or vertigo within minutes of surfacing.
• Chest pain, haemoptysis, dyspnoea, arrhythmia or cardiac arrest.
• Surgical emphysema or pneumothorax from the lung injury.

Red flags.

• Any neurological symptom within 30 minutes of surfacing.
• Unconsciousness, seizures, cardiac signs or breathing difficulty.

• Clinical diagnosis from the history and the timing. Do not delay treatment for imaging.
• Examination of airway, breathing and neurological state; chest examination for pneumothorax.
• Chest radiograph for pneumothorax, pneumomediastinum or other lung disease; CT chest later for blebs or cysts.
• ECG and troponin; glucose.
• Brain CT only when it will not delay transfer, mainly to exclude haemorrhage or other causes.

Differential diagnosis. Decompression sickness (usually later onset and often with pain), stroke, hypoglycaemia, hypoxia, carbon monoxide poisoning, oxygen toxicity seizure, marine envenomation, drowning, head injury.

• Airway, breathing and circulation; oxygen 100% by a tight fitting non-rebreather mask at 15 litres/minute, or by ventilator with 100% oxygen, started at once and continued until recompression.
• Place the patient supine and flat. Head down and left lateral positions are not advised.
• Isotonic fluids: 0.9% sodium chloride 1 litre intravenously over 1 hour, then adjusted to urine output of 0.5 to 1 mL/kg/hour. Avoid glucose containing fluids unless hypoglycaemic. Monitor blood pressure, urine output and heart failure risk.
• Urgent hyperbaric treatment at a diving medicine centre, ideally within 6 hours, though later treatment still helps. The usual first table delivers oxygen at 2.8 atmospheres absolute for about 4 hours 45 minutes, with deeper tables for severe cases directed by the hyperbaric physician. Drain any pneumothorax before compression.
• Seizures: lorazepam 4 mg intravenously over 2 minutes, repeated once after 10 minutes if seizures continue. Maximum 8 mg. Monitor breathing and blood pressure; caution in respiratory depression and hepatic impairment; no renal adjustment.
• Transport by ground, or by aircraft pressurised to sea level, or flown under 300 m.
• Corticosteroids and routine antiplatelet therapy are not advised.

Monitoring. Continuous neurological, cardiac and oxygenation monitoring; repeat neurological examination after each hyperbaric session; further sessions until no further improvement.

Referral and escalation. Emergency call and a diving medicine physician at once; intensive care for unconsciousness or arrest; cardiothoracic review for persistent air leak; occupational and diving medical review before any return to diving, which is usually only after complete recovery and normal chest CT, and recurrent or lung related cases are commonly permanently unfit.