Which set lists the four classic aviation-relevant types of hypoxia?

• A. Hypoxic, Anemic, Histotoxic, and Ischemic
• B. Hypoxic, Anemic, Hyperoxic, and Stagnant
• C. Hypoxic, Anemic, Histotoxic, and Stagnant
• D. Hypoxic, Anemic, Neurologic, and Vascular

Answer: (C)

The four classic aviation hypoxia types focus on where the oxygen problem originates: in the air, in the blood, in the body's ability to use oxygen, or in the circulation delivering it to tissues. Hypoxic hypoxia happens when the ambient oxygen partial pressure is too low (such as at altitude or with cabin depressurization), so less oxygen reaches the blood. Anemic hypoxia occurs when the blood’s capacity to carry oxygen is reduced, due to anemia or toxins like carbon monoxide that lower usable hemoglobin. Histotoxic hypoxia is when cells can’t utilize the oxygen they receive, as with certain poisons that disrupt cellular respiration. Stagnant hypoxia arises from inadequate blood flow or pooling, so oxygen delivery to tissues is insufficient even if the blood is well oxygenated.

That combination—hypoxic, anemic, histotoxic, and stagnant—is the standard quartet used to describe aviation-relevant hypoxia. Other options mix in conditions that aren’t part of this four-category framework, such as hyperoxic (an excess of oxygen rather than a deficiency), ischemic or neurologic or vascular terms that don’t align with the classic four hypoxia types.