What is gas embolism?

Pathophysiology, incidence and the procedures most commonly associated with iatrogenic gas embolism.

Vascular gas embolism occurs when air or another gas enters the bloodstream and obstructs blood flow. In the hospital setting this most commonly occurs during invasive medical procedures, and is known as iatrogenic gas embolism (IGE).

Gas can enter the circulation through arterial or venous routes. This can result in stroke-like symptoms, seizures, cardiovascular collapse or cardiac arrest.

How common is it?

Gas embolism is significantly underdiagnosed. Only around 10 cases per year currently reach hyperbaric treatment in England — a figure that almost certainly represents a small fraction of those who would benefit. Many cases are not recognised, particularly when the patient is anaesthetised or sedated at the time of the event, or when symptoms are attributed to thromboembolic stroke or another cause.

A normal CT does not exclude the diagnosis. Gas is often no longer visible by the time imaging is performed, but the ischaemic and inflammatory injury it has caused persists.

Which procedures carry the highest risk?

Gas embolism can complicate a wide range of procedures. Those most commonly associated with it include:

Higher risk

  • Central venous catheter insertion or removal
  • Sitting-position craniotomy
  • Posterior fossa and neck surgery
  • Cardiac surgery (including valve replacement)
  • Laparoscopic procedures
  • Total hip arthroplasty
  • Craniosynostosis repair

Moderate risk

  • CT-guided percutaneous lung biopsy
  • Haemodialysis
  • Coronary surgery
  • Spinal fusion
  • Cervical laminectomy
  • GI endoscopy
  • Hysteroscopy
  • Contrast radiography

Gas embolism should be considered whenever there is an unexpected periprocedural neurological or cardiovascular event. This list is not exhaustive. The procedures most likely to go unrecognised are those performed on the ward or in the interventional suite, where gas embolism may not be in the differential.

How does gas reach the brain?

Gas can enter the arterial circulation directly — for example during cardiac or thoracic surgery. Alternatively, it can enter the venous system and reach the arterial side through a patent foramen ovale, an arteriovenous malformation, or by overwhelming the filtering capacity of the pulmonary capillary bed. Gas can also travel retrograde through the cerebral venous system when a patient is upright — for example during insertion or removal of a jugular central venous catheter.

Emergency
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