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A-a Gradient

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Calculates the Alveolar-Arterial Gradient to assess degree of shunting and V/Q mismatch . A-a O2 Gradient = [ (FiO2) * (Atmospheric Pressure - H2O Pressure) - (PaCO2/0.8) ] - PaO2 from ABG

A-a O2 Gradient [mmHg] = ( (c/100 * (a - 47) - d/0.8)) - b
Expected A-a Gradient [mmHg] = e/4 + 4
1. Atmospheric Pressure mmHg
2. PaO2 (from ABG) mmHg
3. FiO2 (Room Air: 21%) %
4. PaCO2 mmHg
5. Age (for expected A-a gradient) years