Which type of hypoxia is associated with cyanide poisoning?

• A. Hypoxic hypoxia
• B. Anemic hypoxia
• C. Histotoxic hypoxia
• D. Stagnant hypoxia

Answer: (C)

Cyanide poisoning causes histotoxic hypoxia. In this type, oxygen can reach the tissues, but the cells cannot use it because a toxin blocks the mitochondrial enzymes needed for oxidative phosphorylation. Cyanide inhibits cytochrome c oxidase in the electron transport chain, so aerobic metabolism halts and cells depend on less efficient anaerobic pathways. Blood oxygen content may look normal, yet tissues are effectively starved of usable oxygen, leading to lactic acidosis and other signs of hypoxia despite adequate ventilation and oxygen delivery. This contrasts with hypoxic hypoxia (low arterial oxygen), anemic hypoxia (reduced oxygen-carrying capacity), or stagnant hypoxia (poor circulation), where the underlying issue is not a cellular blockade of oxygen use.