The Aa Gradient Calculator helps medical professionals and students quickly determine the arterial-alveolar oxygen gradient. This key respiratory metric aids in differentiating causes of hypoxemia, assessing lung function, and evaluating gas exchange efficiency for better diagnostic insights into various respiratory conditions.
Formula:
The Aa Gradient (A-aDO2) is calculated using the following formulas:
- Alveolar Oxygen Pressure (PAO2) = (FiO2 / 100) × (Patm - PH2O) - (PaCO2 / R)
- Aa Gradient = PAO2 - PaO2
Where:
- FiO2: Fraction of Inspired Oxygen (as a decimal, e.g., 0.21 for 21%)
- Patm: Atmospheric Pressure (typically 760 mmHg at sea level)
- PH2O: Water Vapor Pressure (typically 47 mmHg at body temperature)
- PaCO2: Arterial Carbon Dioxide Pressure (from ABG)
- R: Respiratory Quotient (typically 0.8)
- PaO2: Arterial Oxygen Pressure (from ABG)