Hypoxia is inadequate tissue oxygenation. Which set lists the four main types relevant to aeromedical transport?

• A. Hypoxic, Metabolic, Infectious, Histotoxic
• B. Hypoxic, Anemic, Anoxic, Histotoxic
• C. Hypoxic, Anemic, Stagnant (circulatory), Hyperoxic
• D. Hypoxic, Anemic, Stagnant (circulatory), Histotoxic

Answer: (D)

Think about hypoxia as not getting enough usable oxygen to tissues, and there are four main ways this can happen in flight. First is hypoxic hypoxia, produced by low oxygen tension in the air we breathe at altitude or by ventilation problems, which reduces the amount of oxygen reaching the blood. Second is anemic hypoxia, where the blood’s carrying capacity is lowered—fewer or dysfunctional hemoglobin molecules means less oxygen is transported to tissues. Third is stagnant (circulatory) hypoxia, caused by insufficient blood flow or pooling that prevents oxygen-rich blood from reaching tissues quickly enough. Fourth is histotoxic hypoxia, where cells can’t use the oxygen they receive due to toxins interfering with cellular metabolism, such as cyanide poisoning. The option listing these four mechanisms matches the classic, clinically relevant set for aeromedical transport, so it’s the best choice. Other options introduce terms like infectious, metabolic, anoxic, or hyperoxic, which do not represent the standard four mechanisms by which oxygen delivery or utilization fails in aviation medicine.