Asphyxia (from Greek a-, "without" and σφυγμός (sphygmos), "pulse, heartbeat") is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of Asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs most sensitive to hypoxia first, such as the brain, hence resulting in cerebral hypoxia. Asphyxia is usually characterized by air hunger, but this is not always the case; the urge to breathe is triggered by rising carbon dioxide levels in the blood rather than diminishing oxygen levels. Sometimes there is not enough carbon dioxide to cause air hunger, and victims become hypoxic without knowing it. This may occur, for example, if the oxygen in the air of an enclosed space is displaced by a large amount of inert gas. In any case, the absence of effective remedial action will very rapidly lead to unconsciousness, brain damage, and death. The time to death is dependent on the particular mechanism of asphyxia.
Asphyxia is used to maim or kill in capital punishment, suicide, torture, and warfare. It is also used non-fatally in martial arts, combat sports, BDSM, and during sex as erotic asphyxia. Because the need to breathe is triggered by the level of carbon dioxide in the blood, some victims may not experience an urgent need to breathe and may remain unaware of the onset of hypoxia.
Chemical or physiological interference with respiration
Various chemical and physiological situations can interfere with the body's ability to absorb and use oxygen or regulate blood oxygen levels:
- Carbon monoxide inhalation, such as from a car exhaust: carbon monoxide has a higher affinity than oxygen to the hemoglobin in the blood's red blood corpuscles, bonding with it tenaciously, and, in the process, displacing oxygen and preventing the blood from transporting it around the body
- Contact with certain chemicals, including pulmonary agents (such as phosgene) and blood agents (such as hydrogen cyanide)
- Self-induced hypocapnia by hyperventilation, as in shallow water or deep water blackout and the choking game
- A seizure which stops breathing activity
- Sleep apnea
- Drug overdose
- Ondine's curse, central alveolar hypoventilation syndrome, or primary alveolar hypoventilation, a disorder of the autonomic nervous system in which a patient must consciously breathe; although it is often said that persons with this disease will die if they fall asleep, this is not usually the case
- Acute respiratory distress syndrome.
- Exposure to extreme low air pressure or vacuum.
Smothering refers to the mechanical obstruction of the flow of air from the environment into the mouth and/or nostrils, for instance, by covering the mouth and nose with a hand, pillow, or a plastic bag. Smothering can be either partial or complete, where partial indicates that the person being smothered is able to inhale some air, although less than required. In a normal situation, smothering requires at least partial obstruction of both the nasal cavities and the mouth to lead to asphyxia. Smothering with the hands or chest is used in some combat sports to distract the opponent, and create openings for transitions, as the opponent is forced to react to the smothering. It is also used in BDSM as a type of facesitting.
In some cases, smothering is combined with simultaneous compressive asphyxia. One example is overlay, in which an adult accidentally rolls over an infant during co-sleeping, an accident that often goes unnoticed and is mistakenly thought to be sudden infant death syndrome. Other accidents involving a similar mechanism are cave-ins or when an individual is buried in sand or grain. In homicidal cases, the term burking is often ascribed to a killing method that involves simultaneous smothering and compression of the torso.
Compressive asphyxia (also called chest compression) refers to the mechanical limitation of the expansion of the lungs by compressing the torso, hence interfering with breathing. Compressive asphyxia occurs when the chest or abdomen is compressed posteriorly. In accidents, the term traumatic asphyxia or crush asphyxia is usually used to describe compressive asphyxia resulting from being crushed or pinned under a large weight or force.
Positional asphyxia (also known as postural asphyxia) occurs when someone's position prevents adequate breathing. Positional asphyxia is a potential danger of some physical restraint techniques.
People may die from positional asphyxia by simply getting themselves into a breathing-restricted position they cannot get out of, either through carelessness or as a consequence of an accident.