Calculations must be re-checked, shouldn't be used alone for patient care, and don't substitute for professional judgment. See our full disclaimer.
Assesses for degree of shunting and V/Q mismatch.
A-a O2 Gradient = [ (FiO2) * (Atmospheric Pressure - H2O Pressure) - (PaCO2/0.8) ] -
PaO2 from ABG
Normal Gradient Estimate = (Age/4) + 4
The 5 Causes of Hypoxemia, #1-3 have an elevated A-a Gradient:
Calculations must be re-checked and should not be used alone to guide patient care nor should they substitute for clinical judgement. disclaimer