Which statement best defines hypoxic hypoxia?

• A. Hypemic hypoxia caused by insufficient blood oxygen-carrying capacity.
• B. Stagnant hypoxia due to reduced blood flow.
• C. Hypoxic hypoxia caused by insufficient oxygen available to the lungs due to low ambient oxygen pressure.
• D. Histotoxic hypoxia caused by inability of cells to use oxygen.

Answer: (C)

Hypoxic hypoxia occurs when there isn’t enough oxygen available to the lungs because the ambient oxygen pressure is too low, such as at altitude. When barometric pressure drops, the partial pressure of inspired oxygen falls, so the alveolar oxygen level and the amount of oxygen that can diffuse into the blood are reduced. Even with normal blood function and good circulation, arterial oxygen content is lower, and tissues receive less oxygen. This differentiates it from hypemic hypoxia (insufficient blood’s oxygen-carrying capacity), stagnant hypoxia (reduced blood flow), and histotoxic hypoxia (cells can’t use the oxygen). So the best definition is oxygen availability to the lungs being limited by low ambient oxygen pressure.