As altitude increases, what happens to blood oxygen saturation?

As altitude increases, what happens to blood oxygen saturation?

• A. Increases
• B. Remains unchanged
• C. Decreases leading to hypoxia
• D. Fluctuates without pattern

Answer: (C)

As you climb, the surrounding air pressure drops, so the partial pressure of oxygen available to breathe decreases. This lowers the oxygen tension in the alveoli and, consequently, in arterial blood. Since hemoglobin saturation depends on this arterial oxygen tension, SaO2 falls as altitude rises. If the saturation drops enough or tissue oxygen delivery can’t meet demand, you develop hypoxia. So the best answer is that blood oxygen saturation decreases leading to hypoxia. Note: while acclimatization can slow or partially offset this effect (through increased ventilation, higher red blood cell production, etc.), the fundamental relationship with altitude is a downward trend in saturation.

As you climb, the surrounding air pressure drops, so the partial pressure of oxygen available to breathe decreases. This lowers the oxygen tension in the alveoli and, consequently, in arterial blood. Since hemoglobin saturation depends on this arterial oxygen tension, SaO2 falls as altitude rises. If the saturation drops enough or tissue oxygen delivery can’t meet demand, you develop hypoxia. So the best answer is that blood oxygen saturation decreases leading to hypoxia.

Note: while acclimatization can slow or partially offset this effect (through increased ventilation, higher red blood cell production, etc.), the fundamental relationship with altitude is a downward trend in saturation.