A-a Gradient

The alveolar-arterial (A-a) oxygen gradient measures the difference between alveolar and arterial oxygen concentrations. It helps assess the efficiency of oxygen transfer across the alveolar membrane.

Disclaimer

This calculator is for educational purposes only. Always verify with clinical judgment.

Calculator

FiO2 (fraction, e.g. 0.21)

PaCO2 (mmHg)

PaO2 (mmHg)

Atmospheric Pressure (mmHg)

Water Vapor Pressure (mmHg)

Respiratory Quotient (RQ)

Formula

A-a = [FiO2 × (Patm - PH2O) - (PaCO2 / RQ)] - PaO2

References

West JB. Respiratory Physiology: The Essentials, 10th Edition.
Hess DR, Kacmarek RM. Essentials of Mechanical Ventilation, 4th Edition.