Asphyxia
Definition
- Asphyxia is defined as lack of oxygen in blood and tissues due to impaired or absence of exchange of oxygen and carbon dioxide on a ventilatory basis, leading to death.
Etiology
Asphyxia can develop because of several causes such as:
- Physical causes—breathing in high altitudes with rarefied/vitiated medium, deficient of O2, e.g. mountaineering.
- Inhaling irrespirable gases, such as gases interfering with normal O2 carrying capacity of blood haemoglobin, e.g. CO, CO2, H2S, etc. or gases which prevent cellular oxidation enzymes, e.g. HCN.
- Drugs/poisons—directly depressing the respiratory centres, e.g. narcotics (morphine), anaesthetics, etc.
- Mechanical asphyxia—this is due to mechanical interference to respiration, e.g. hanging, strangulation, throttling, smothering, choking, drowning, etc.
- Pathological asphyxia—this is due to diseases, e.g. lung pathology.
- Allergic reactions causing laryngeal oedema.
Pathophysiology
- Conventionally, the term asphyxia has been applied to all conditions in which oxygen supply to blood and tissue has been reduced appreciably below the normal working level by any interference with respiration.
- In death from asphyxia, usually it falls below the minimum necessary for continuance of life.
- Serious deprivation of oxygen for 5 to 10 minutes can result in permanent damage to central nervous system and cardiovascular system resulting in death.
- It is interesting to note that in a healthy adult body, normally blood that is circulating has about 1 litre of oxygen held in combination. Any interference with this results in asphyxia, which in turn triggers the consequences. This renders the pathophysiology of asphyxia.
Anoxia
- According to physiological concepts, asphyxia can lead to lack of oxygen supply to cells and tissues. Among all, nervous tissues are affected first by oxygen deficiency. This lack of oxygen supply is known as anoxia.
