For licensed healthcare professionals only. Not a diagnostic tool. See full disclaimer.
Alveolar Gas Equation Calculator
Input
%
mmHg
mmHg
Alveolar PO₂ (PAO₂)
—
About
The alveolar gas equation calculates the partial pressure of oxygen in the alveoli (PAO₂). It is fundamental to understanding gas exchange and is used to calculate the A-a gradient. PAO₂ depends on the fraction of inspired oxygen (FiO₂), atmospheric pressure, water vapor pressure, PaCO₂, and the respiratory quotient (RQ).
Formula
PAO₂ = FiO₂ × (Patm − PH₂O) − (PaCO₂ / RQ)
PH₂O = 47 mmHg (water vapor pressure at 37°C)
RQ = Respiratory Quotient (typically 0.8 on mixed diet)
At sea level, room air: PAO₂ = 0.21 × (760 − 47) − (40 / 0.8) ≈ 100 mmHg
Interpretation
| PAO₂ (mmHg) | Interpretation |
|---|---|
| ≥ 80 | Normal |
| 60 – 79 | Mildly reduced |
| < 60 | Significantly reduced |
References
- West JB. Respiratory Physiology: The Essentials. 10th ed. Wolters Kluwer; 2015.
- Curran-Everett D. A classic learning opportunity from Fenn, Rahn, and Otis (1946): the alveolar gas equation. Adv Physiol Educ. 2006;30(2):58-62.
FAQ
Disclaimer
For educational and informational purposes only. Not intended to replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.