Recognition and diagnosis
Gas embolism is a clinical diagnosis. Maintain a high index of suspicion when any neurological or cardiovascular event occurs during, or within minutes to hours of, an invasive procedure.
Gas embolism is a clinical diagnosis. It should be considered whenever unexplained neurological or cardiovascular deterioration occurs during or shortly after an invasive procedure — particularly those involving central venous access, cardiac surgery, or neurosurgery in the sitting position. Most cases present immediately or within the early recovery period. Diagnosis is frequently delayed not because symptoms appear late, but because the possibility is not considered.
The presentation can be indistinguishable from thromboembolic stroke. In a periprocedural context, assume gas embolism first.
What does it look like?
In the awake patient
Restlessness, anxiety, a sense of impending doom. Dyspnoea, chest pain, and neurological symptoms including confusion, visual disturbance, speech difficulty, weakness or altered consciousness.
Cardiovascular signs
Cardiovascular collapse requiring CPR, hypotension, arrhythmias, transient hypoxia as gas passes through the pulmonary vessels. A characteristic mill-wheel murmur may be audible, caused by gas churning in the cardiac chambers.
Neurological signs
These may be subtle or catastrophic: altered mental status, seizures, hemiparesis, pupil abnormalities or coma. Importantly, signs are often not confined to a single vascular territory — a feature that can help distinguish CAGE from thromboembolic stroke, though the distinction should not delay referral.
The critical rule: A periprocedural stroke or neurological event should be treated as gas embolism with cerebral involvement until proven otherwise.
Imaging
CT of the head and chest should be arranged urgently, but imaging must not delay hyperbaric referral in clinically obvious cases. The purpose of CT is to exclude other pathology — particularly intracranial haemorrhage — not to confirm gas embolism.
Absence does not mean exclusion: CT sensitivity for gas embolism is approximately 67%. Gas bubbles may be reabsorbed or redistributed before imaging is performed, but the ischaemic and inflammatory damage they cause persists. A normal CT does not exclude the diagnosis.