# Aa Gradient Formula

A-a Gradient is used in diagnosing the source of hypoxemia. Hypoxemia with a normal gradient suggests Hypoventilation, Low FiO2. Here is the Aa gradient formula for calculating the alveolar arterial gradient and estimated normal gradient. According to this Alveolar arterial gradient formula, to calculate estimated normal gradient just divide patients age by 4 and add it with 4. A-a gradient helps to assess the integrity of the alveolar-capillary unit.

# Alveolar Arterial Gradient Formula

#### Formula:

a = (FiO2 / 100) × (Patm - PH2O) - PaCO2 / r - PaO2
e = (g / 4) + 4

Where,

a = A-a Gradient
FiO2 = Fraction of Inspired Oxygen
Patm = Atmospheric Pressure
PH2O = Water Vapor Pressure
PaCO2 = Partial Pressure of Arterial CO2
r = Respiratory Quotient (RQ)
PaO2 = Partial Pressure of Arterial O2
e = Estimated Normal Gradient
g = Patients Age

#### Related Calculator:

For a young adult non-smoker breathing air, is between 5-10 mmHg in normal A-a gradient. This Aa Gradient Formula page provides you the individual formulas for Aa gradient and estimated normal gradient. Also, you can use the related calculator designed based on the Alveolar arterial gradient formula to check your results.