Gas Embolism

What is Gas Embolism?

Gas Embolism, or the presence of bubbles of air or any other gas in the bloodstream, varies widely and its consequences range from mild discomfort to causing rapid death and can also be caused by various surgical procedures, as well as diving accidents.  Upon entering the vascular system, gas bubbles follow the blood stream until they obstruct small vessels.  Depending on the access route, gas embolism may be classified as venous or arterial gas embolism.  Diagnosis is based on the sudden occurrence of neurological and/or cardiac manifestations.

Examples of the origins of air or gas bubbles in the circulation are:

  • Pulmonary barotrauma (from sudden decompression) as a result of a diving accident
  • Intravascular equipment used during a surgical procedure
    • Intravenous fluids and giving sets, and CVP cannula disconnections
    • Arterial cannula disconnections
    • Angiographic accidents
    • Haemodialysis line disconnections and pump malfunctions
  • Peri-operative
    • Neurosurgical (i.e. posterior cranial fossa)
    • Vascular (i.e. arterial by-pass)
    • Cardiac (i.e. open heart)
    • Thoracic (i.e. pneumonectomy or lobectomy)
  • Orthopaedic (instruments using compressed air)

The main symptom is the sudden occurrence of a combination of neurological and/or cardiovascular signs which can be delayed by just a few minutes or several hours after the causing event.

Primary injury

The pulmonary circulation generally filters bubbles in systemic veins.  A right-to-left shunt in the heart can by-pass this filter.  Bubbles in the pulmonary veins can travel rapidly through the left side of the heart, and reach the systemic arteries, and thus the brain. The effect may appear like a cerebrovascular accident (stroke) from any other cause.  Once in the cerebral vessels, the effects of these bubbles are:

  • Obstruction to blood flow
  • Direct damage to endothelium
  • Platelet release and activation
  • Fibrin release and adhesion to endothelium
  • Vasospasm followed by vasodilatation
  • Opening of the blood brain barrier
  • Cerebral oedema and raised intracranial pressure

 Once suspected, treatment for Gas Embolism must begin at once, the source identified and eliminated, life support be instituted as required and Hyperbaric Oxygen provided as quickly as possible. 

How does Hyperbaric Oxygen treatment work?

  • Reduces the size of bubbles (Boyle’s Law)
  • Removes nitrogen from bubbles by removing nitrogen from the blood and tissue
  • Improves oxygen delivery to tissues damaged by ischaemia
  • Reduces intra-cranial pressure by causing constriction of cerebral arteries
  • Reduces oedema by causing constriction of local arterioles
  • Accelerates wound healing
  • Enhances the immune response of hypoxic tissues
  • Protects against the effects of oxygen free-radicals (if given during reperfusion)
Pressures of 3 ATA are sometimes used, but for a maximum of one hour in the first instance, and with air-breaks in order to minimise oxygen toxicity.  Further Hyperbaric Oxygen treatments are determined by the clinical progress of the individual patient and continued until resolution of all symptoms or failure to achieve further improvement.  In some cases anti-convulsions may also be necessary.
There is no dispute about the applicability of Hyperbaric Oxygen in this condition, however, its recognition in clinical practice is difficult and very few cases are referred to Hyperbaric Medicine departments.
The rarity of each of these conditions in any one centre makes it unlikely that many surgeons have seen what can be achieved by using Hyperbaric Oxygen in addition to conventional management.  Controlled trials are also difficult to perform, since the ethics of withholding Hyperbaric Oxygen from the control group are doubtful.  Where Hyperbaric Oxygen helps to prevent the amputation of an extremity, its cost-effectiveness is likely to be high, considering the cost of supporting the patient who is so disabled. The close association of all specialists involved is essential.

Always remember, you’re better safe than sorry – As the symptoms for DCI are so diverse, any symptom that cannot be readily explained after diving or other hyperbaric exposure should be assumed to be DCI until proven otherwise.

Call Divers Emergency Service on 07 999 292 999 if you suspect you or anyone diving with you has DCI or the Bends.

 

References for evidence
Kindwall E (ed), Hyperbaric Medicine Practice 2nd ed., Chapter 19.D.
Mathieu (ed.) – Handbook on Hyperbaric Medicine, 217-238. 2006