Dive history may eliminate decompression sickness in many cases, and the presence of symptoms of other lung overexpansion injury would raise the probability of gas embolism. Treatment
A large bubble of air in the heart (as can follow certain traumas in which air freely gains access to large veins) will present with a constant "machinery" murmur. It is important to promptly place the patient in Trendelenburg position (head down) and on their left side (left lateral decubitus position). The Trendelendburg position keeps a left-ventricular air bubble away from the coronary artery ostia (which are near the aortic valve) so that air bubbles do not enter and occlude the coronary arteries (which would cause a heart attack). Left lateral decubitus positioning helps to trap air in the non-dependent segment of the right ventricle (where it is more likely to remain instead of progressing into the pulmonary artery and occluding it). The left lateral decubitus position also prevents the air from passing through a potentially patent foramen ovale (present in as many as 30% of adults) and entering the left ventricle, from which it could then embolise to distal arteries (potentially causing occlusive symptoms such as stroke).Administration of high percentage oxygen is recommended for both venous and arterial air embolism.
The symptoms may be subtle and not immediately noticeable, and may develop for some time after surfacing. Ventilator induced pulmonary barotrauma
Trauma to the lung can also cause an air embolism. This may happen after a patient is placed on a ventilator and air is forced into an injured vein or artery, causing sudden death. Breath-holding while ascending from scuba diving may also force lung air into pulmonary arteries or veins in a similar manner, due to the pressure difference. Direct injection
Air can be injected directly into a vein or artery accidentally during clinical procedures. Misuse of a syringe to meticulously remove air from the vascular tubing of a hemodialysis circuit can allow air into the vascular system. Venous air embolism is a rare complication of diagnostic and therapeutic procedures requiring catheterization of a vein or artery. If a significant embolism occurs, the cardiovascular, pulmonary, or central nervous system may be affected. Interventions to remove or mitigate the embolism may include procedures to reduce bubble size, or withdrawal of air from the right atrium.The lethal dose for humans is considered theoretically between 3 and 5 ml per kg. It is estimated that 300-500 ml of gas introduced at a rate of 100 ml per sec would prove fatal. Mechanism
Air embolism can occur whenever a blood vessel is open and a pressure gradient exists favoring entry of gas. Because the circulatory pressure in most arteries and veins is greater than atmospheric pressure, an air embolus does not often happen when a blood vessel is injured.