PAO2 = (FiO2 [Patm - PH2O]) - (PaCO2 /
R)
PAO2 = (0.21 [760-47]) - (PaCO2 / 0.8)
Where:
- FiO2 = 0.21 at room air
- Patm = 760 mmHg at sea level
- PH2O = 47 mmHg at 37ºC
- PaCO2 = measured from Blood Gas
- R = resp quotient ~ approx 0.8 at steady state, varies with
utilization of macromolecules
Results:
Can help differentiate cause of hypoxemia as being extrapulmonary (e.g.
hypoventilation) vs intrapulmonary (intrinsic lung disease)
Normal: <20 mmHg
Widened >20 mmHg (suggestive
of underlying lung disease)