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 air embolism which shows symptoms is relatively rare. Large emboli can be rapidly fatal.
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 line 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 directly 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, usually this will neither 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 may have happened occasionally, however.
Air embolism can also occur during other types of surgery such as Cesarean section and orthopedic procedures. A few cases have even been reported as a result of sexual intercourse during late pregnancy.
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.
Avoidance in medicine
One can reduce the risk of air embolism by avoiding unnecessary use of syringes and taking all steps to protect the body, noting that it is important never to inject an air-filled syringe straight into the bloodstream. However, usually this will neither suddenly stop the heart nor cause instant death, contrary to various fiction stories where this is used as a method of murder. Murder by air injection may have happened occasionally in the real world.
Gas embolism in diving
Gas embolism (as opposed to an air embolism), is one of the diving disorders SCUBA divers sometimes suffer when they receive pressure damage to their lungs following a rapid ascent. It is named "gas" because the diver may be using a diving breathing gas other than air. The gas bubbles can impede the flow of oxygen-rich blood to the brain and vital organs. They can also cause clots to form in blood vessels.
Gas embolism and decompression sickness (DCS) are very difficult to distinguish, as they have very similar symptoms. The treatment for both is the same, because they are both the result of gas bubbles in the body. In a diving context, the two are often called decompression illness (DCI).
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 rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators.