Asphyxia

Asphyxia is a condition in which the tissues are deprived of oxygen, usually while carbon dioxide accumulates in the blood, leading to unconsciousness and, unless it is reversed, death. The brain and heart are the most vulnerable organs. Starved of oxygen, cells switch to anaerobic metabolism, lactic acid builds up and irreversible damage to brain cells can begin within minutes.

Forensic pathologists group its causes broadly. Mechanical asphyxia includes a blocked airway, as in choking or smothering; pressure on the neck, as in hanging and manual or ligature strangulation; and compression of the chest that stops breathing, as in crush incidents or positional asphyxia, where the body is trapped in a posture that prevents breathing. Drowning is often treated as its own category. Environmental asphyxia happens in air with too little oxygen, such as a sealed tank, and chemical asphyxiants such as carbon monoxide and cyanide stop the blood carrying oxygen or the cells using it.

At autopsy, the classic findings of pinpoint bleeds (petechiae), a congested face and bluish skin (cyanosis) are suggestive but not specific, so the diagnosis depends on the scene, marks such as a ligature groove, and toxicology. In medicine the word also appears in birth asphyxia, when a newborn is short of oxygen around the time of delivery.