An air embolism, or more generally gas embolism, is a medical condition caused by gas bubbles in the bloodstream. Small amounts of air often get into the blood circulation accidentally during surgery and other medical procedures, but an air embolism which shows symptoms is very rare.
Air embolism can occur whenever a blood vessel is open and a pressure gradient exists favoring entry of gas. Because the pressure in most arteries and veins is greater than atmospheric, an air embolus does not always happen when a blood vessel is injured. In the veins above the heart, such as in the head and neck, the pressure is less than atmospheric and an injury may let air in. This is one reason why surgeons must be particularly careful when operating on the brain, and why the head of the bed is tilted down when inserting or removing a central venous catheter from the jugular or subclavian veins.
Trauma to the lung can also cause an air embolism. This is often noticed after the patient is placed on a ventilator and air is forced into an injured vein causing sudden death.
Air can be injected directly into the veins either accidentally or as a deliberate act. Examples include misuse of a syringe, and industrial injury resulting from use of compressed air. However, this will NOT suddenly stop the heart nor cause instant death, unlike in fiction stories where this is used as a method of murder. Murder by air injection is an urban legend.
Air embolism can also occur during other types of surgery such as Caesarean section and orthopedic procedures.
When air enters the veins it travels to the right side of the heart and then to the lungs. This can cause the vessels of the lung to constrict, raising the pressure in the right side of the heart. If the pressure rises high enough in a patient who is one of the 20% to 30% of the population with a patent foramen ovale, the gas bubble can then travel to the left side of the heart and on to the brain or coronary arteries. When death occurs, it is usually the result of a large bubble of gas stopping blood from flowing from the right ventricle to the lungs.
Symptoms of an air embolism depend on where the bubbles lodge. They range from skin rashes, joint pain, visual disturbances, balance disturbances, breathing difficulties, extreme fatigue/lack of strength, numbness, paralysis, unconsciousness and death. If the embolism occurs in the coronary arteries of the heart, a heart attack will occur. If it lodges in the lungs, a pulmonary embolism will occur, resulting in shortness of breath and chest pain.
Recompression is the only lasting treatment of an air embolism. Normally this is carried out in a recompression chamber.
Oxygen first aid treatment is useful for suspected gas embolism casualties or divers who have made fast ascents or missed decompression stops. Most fully closed-circuit re-breathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators.