Arterial Gas Embolism

Arterial gas embolism occurs when nitrogen bubbles escape in to the arterial circulation. This can result from a few different mechanisms:

i. PULMONARY BAROTRAUMA. This is an important condition to remember when dealing with divers. As per Boyle’s law, gas expands in volume as pressure decreases. Therefore the air in a divers lungs expands as the diver makes their way to the surface. If a diver doesnt equalise the pressure (holds their breath on ascent) or has an underlying pulmonary disease (causing gas trapping in the lungs) an over inflation injury can occur. Air from the pneumothorax can then embolise in to the pulmonary circulation, and reach the left side of the heart, to then be pumped in to the systemic arteries. This causes an arterial gas embolism.

ii. PATENT FORAMEN OVALE/ ARTERIOVENOUS MALFORMATION (right to left shunt). Any bubbles in the venous circulation which may not normally cause a problem shunt in the arterial circulation and become an AGE.

iii. OVERWHELMING THE PULMONARY FILTER. Most divers bubble after most dives these bubbles usually diffuse in to the alveoli where they are exhaled. If this filter is overwhelmed, for example due to exercise, the bubbles will pass through the lungs without being filtered out and will then pass in to the arterial circulation via the left heart.

The escaped gas (AGE) can then lodge anywhere in the arterial system, causing arterial occlusion and resulting ischemia. The most serious form is when a gas embolus lodges in the cerebral arterial circulation known as a cerebral arterial gas embolus (CAGE).

Due to the pathophysiology of AGE, symptoms usually have a quick onset and patients need swift recompression in order to reduce permanent irreversible damage caused by tissue ischaemia.

Learning Bite

Decompression illness can be caused by evolved gas (DCS) or escaped gas (AGE). There are two ways in which bubbles can cause damage to tissues: directly or by resulting inflammatory processes.