- 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.
According to Gordon, anoxia is classified as follows:
- Anoxic Anoxia : Here oxygen cannot gain entry into the blood, e.g. hanging with obstruction of trachea—here no oxygen enters the pulmonary circulation, hence, there is no oxygen in the blood.
- Anemic Anoxia : Here oxygen can get into blood, but the blood is incapable of carrying it, e.g. carbon monoxide poisoning, wherein the carboxyhemoglobin formed prevents blood oxygenation.
- Stagnant Anoxia : Here oxygen can get into the blood, blood is capable of carrying it, but circulation is at failure, e.g. congestive cardiac failure.
- Histotoxic Anoxia : Here oxygen can get into the blood, blood is capable of carrying it, and the blood circulation is perfectly normal, but the cell cannot utilize the oxygen available in blood, e.g. cyanide poisoning, here the cyanides destroy the cellular oxygen enzyme system cytochrome oxidases.
Histotoxic anoxia can be further classified as follows:
- Extracellular histotoxic anoxia – Here oxygen cannot be taken up due to the failure of tissue enzyme system by poisoning, e.g. cyanide, overdose of hypnotics or anaesthetics.
- Pericellular histotoxic anoxia – Here oxygen cannot be taken up due to reduced permeability of cell membrane, e.g. lipoid soluble anaethestic agents such as chloroform, halothane, etc.
- Substrate histotoxic anoxia – Here oxygen cannot be taken up due to failure of efficient cell metabolism, e.g. hypogylcaemia, etc.
- Metabolite histotoxic anoxia – Here oxygen cannot be taken up due to the accumulation of end products of cell respiration, e.g. carbon dioxide poisoning, uremia, etc.