Small amounts of air often get into the blood circulation accidentally during surgery and other medical procedures (for example a bubble entering an intravenous fluid line), but most of these air emboli enter the veins and are stopped at the lungs, and thus a venous air embolism that shows any symptoms is very rare.[2]
For venous air embolisms, death may occur if a large bubble of gas becomes lodged in the heart, stopping blood from flowing from the right ventricle to the lungs.[3][4] However, experiments on animals show that the amount of gas necessary for this to happen is quite variable.[5] Human case reports suggest that injecting more than 100 mL of air into the venous system at rates greater than 100 mL/s can be fatal.[6] Very large and symptomatic amounts of venous air emboli may also occur in rapid decompression in severe diving or decompression accidents, where they may interfere with circulation in the lungs and result in respiratory distress and hypoxia.[7]
Gas embolism into an artery, termed arterial gas embolism (AGE), is a more serious matter than in a vein, because a gas bubble in an artery may directly stop blood flow to an area fed by the artery. The symptoms of 'AGE' depend on the area of blood flow, and may be those of stroke or heart attack if the brain or heart, respectively, is affected.[7] The amount of arterial gas embolism that causes symptoms depends on location - 2 mL of air in the cerebral circulation can be fatal, while 0.5 mL of air into a coronary artery can cause cardiac arrest.[8][9]
