PiO2 value when FiO2 is 0.21 at sea level is approximately?

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PiO2 value when FiO2 is 0.21 at sea level is approximately?

The value being tested is the inspired oxygen partial pressure (PiO2) at sea level, which is determined by how much oxygen you’re breathing (FiO2) and the pressure of the air after removing the water vapor that humidifies the inspired gas. At sea level, barometric pressure is about 760 mmHg and the water vapor pressure in the humidified air at body temperature is about 47 mmHg. So PiO2 = FiO2 × (Pb − PH2O) = 0.21 × (760 − 47) ≈ 0.21 × 713 ≈ 149.7 mmHg. That’s why the value is about 149.7 mmHg. The other numbers don’t fit this standard sea-level, humidified-air calculation; they would require a different FiO2 or different ambient pressure/humidity conditions.

The value being tested is the inspired oxygen partial pressure (PiO2) at sea level, which is determined by how much oxygen you’re breathing (FiO2) and the pressure of the air after removing the water vapor that humidifies the inspired gas. At sea level, barometric pressure is about 760 mmHg and the water vapor pressure in the humidified air at body temperature is about 47 mmHg. So PiO2 = FiO2 × (Pb − PH2O) = 0.21 × (760 − 47) ≈ 0.21 × 713 ≈ 149.7 mmHg. That’s why the value is about 149.7 mmHg.

The other numbers don’t fit this standard sea-level, humidified-air calculation; they would require a different FiO2 or different ambient pressure/humidity conditions.

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