Which type of hypoxia occurs when tissues cannot use oxygen due to cyanide or narcotics?

• A. Hypoxic Hypoxia
• B. Hypemic Hypoxia
• C. Stagnant Hypoxia
• D. Histotoxic Hypoxia

Answer: (D)

Histotoxic hypoxia occurs when tissues cannot use oxygen even though it is being delivered. Toxic agents like cyanide block cellular respiration in mitochondria, preventing oxidative phosphorylation, so cells can’t extract energy from oxygen and must rely on less efficient anaerobic metabolism. Narcotics can contribute to this by impairing cellular processes that use oxygen, but the defining feature is the body's inability to utilize oxygen at the cellular level, not a shortage of oxygen supply itself. This differs from hypoxic hypoxia (insufficient oxygen reaching the blood), hypemic hypoxia (blood’s oxygen-carrying capacity is reduced), or stagnant hypoxia (impaired blood flow).