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Air embolism means gas bubbles within the circulation obstructing vascular flow and causing ischemia. Air may be introduced into the systemic circulation under a number of circumstances. These include: - Operations in the head and neck where a large vein is opened inadvertently. - In chest injury, air escapes from lung after rib fracture. - Mismanagement of blood transfusions where positive pressure is being used to speed up the flow of blood. - During hemodialysis for renal failure. - Following insufflation of air into the fallopian tubes in the course of investigation of sterility. - Interference with the placental site during criminal abortion.
The air enters the right side of the heart where, in the right ventricle, it is whipped up into a frothy mass. This mass can block the flow of blood through the pulmonary arteries. The clinical picture that develops closely mimics that of massive pulmonary embolization by thrombus derived from the leg veins. In some cases the froth may gain access to the systemic arterial circulation and impact there. The most frequent site for this is the brain, but cases have also been reported of embolization of vessels supplying the spinal cord, with patients being investigated for sterility becoming quadriplegic following tubal insufflation. As little as 40 ml of air can have serious clinical results and 100 ml can be fatal, though there have been rare cases in which 200 ml have been tolerated. If air embolism is suspected as the cause of death, it is necessary to place the heart and pulmonary arteries under water when they are opened, in order to detect the escape of the air bubbles from the blocked vessels.
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