Histotoxic hypoxia (also called histoxic hypoxia) is the inability of cells to take up or utilize oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues. Histotoxic hypoxia results from tissue poisoning, such as that caused by cyanide (which acts by inhibiting cytochrome oxidase), and certain other poisons like hydrogen sulfide (byproduct of sewage and used in leather tanning).
Histotoxic hypoxia refers to a reduction in ATP production by the mitochondria due to a defect in the cellular usage of oxygen. An example of histotoxic hypoxia is cyanide poisoning. There is a profound drop in tissue oxygen consumption since the reaction of oxygen with cytochrome c oxidase is blocked by the presence of cyanide. There are other chemicals that interrupt the mitochondrial electron transport chain (e.g., rotenone, antimycin A) and produce effects on tissue oxygenation similar to that of cyanide. Oxygen extraction decreases in parallel with the lower oxygen consumption, with a resulting increase in venous oxygen content and PvO2. Although cyanide stimulates the peripheral respiratory chemoreceptors, increasing the inspired oxygen fraction is not helpful, since there is already an adequate amount of oxygen which the poisoned cells cannot use.