Asphyxia is defined as when the body does not receive enough oxygen though means of either oxygen delivery or utilization of the oxygen supplied. The tissues and organs of the body do not receive enough oxygen to sustain normal functioning. There are several causes of asphyxia, and they can be broken down into these categories.
- Compression: This category includes the compression of the neck resulting in a lack of oxygen. This can occur with the process of hanging or through strangulation. Compression of the chest is another method of asphyxia related to the inability of the chest to expand and contract. This can be the result of a very heavy object lying on top of the chest or even a person “sitting” on the chest. This chart provides the amount of compression pressure needed on the neck structures to cause unconsciousness and/or death.
- Obstruction: An obstruction of the airway can cause asphyxia. The obstruction could be mechanical, such as swelling in the throat from an allergic reaction or structural swelling of tissue, or from a physical obstruction such as a foreign body inserted into the throat.
- Exclusion: This category includes the lack of oxygen related to the environment in terms of oxygen depletion from other gases. This can occur with the inhalation of other cases such as with chemical exposures, carbon dioxide exposure, and carbon monoxide, and cyanide exposure caused from fires.
Death due to the process of asphyxia can be a challenge in its investigation. In not all circumstances is the evidence present as to how the asphyxiation occurred. Obvious ligature marks and/or compressive objects on the chest are not always present and the scene may not always provide the answers. For example, in child smothering cases, there may be no obvious physical signs of the asphyxial cause and the autopsy may also not clearly provide the manner of death. Evidence of hypoxia (oxygen deprivation) will not be apparent on autopsy unless the child has survived for a period of time after the asphyxial event, such as with resuscitation.