Following phases are included in the Hypoxia mechanism :
1. Anoxic hypoxia—Gas phase. There is inadequate supply of oxygen to the lungs, or the lung is not functioning properly.
2. Anaemic hypoxia—Fluid hypoxia (phase). There is a decrease in the oxygen carrying capacity of the blood.
3. Stagnant hypoxia—Fluid phase. There is decreases circulation of blood and thus oxygen is not delivered.
4. Histotoxic hypoxia—Tissue phase. There is a defect in the extraction of oxygen from the blood by the body tissues.
These four hypoxia mechanism are involved in the different types of injuries to the body organs because of lack of oxygen or inadequate supply of it.
Hepatocellular death often results from hypoxia or anoxia. Hypoxia decreases intracellular ATP. Thus hypoxia mechanism for liver injury is essentially due to lack of ATP.
This stimulates breakdown of glycogen and anaerobic glycolysis, which raises lactic acid levels and lowers intracellular pH. Sudden, precipitous decreases in ATP initiate a series of events that may culminate in hepatocellular necrosis.
All inhaled anesthetics depress the ventilatory responses to hypercapnia and hypoxia by altering central and peripheral chemoreceptor function in a dose-dependent fashion.
The effects of subanesthetic concentrations of inhaled agents on hypercapnic responses are controversial. Inhibition of hypoxic responses by subanesthetic concentrations of volatile agents depends on the agent used and perhaps the baseline state of central nervous system arousal.
In all the four hypoxia mechanism that have been discussed the main basis is either the defiency of oxygen being absorbed by the lungs, or the defect in blood circulation and thus oxygen supply or, the defect in the extraction of oxygen from the blood by the body tissues.