A-a Oxygen Gradient

Arterial O2 partial pressure - PaO2:
Arterial CO2 partial pressure - PaCO2:
Atmospheric Pressure:
Inspired Oxygen Concentration (FiO2):
Room Air (21%)


A-a Gradient:

Computational notes

A-a gradient is calculated as follows (all units mmHg):

A-a (O2) = (FiO2) * (Patm - 47) - (PaCO2/0.8) - PaO2


  1. Helmholz HF Jr (1979) The abbreviated alveolar air equation. Chest 75:748.

Disclaimer: The authors make no claims of the accuracy of the information contained on this web page. Your reliance upon information and content obtained at or through this website is solely at your own risk. All calculations must be confirmed before use. The authors shall not be liable for any special, consequential, or exemplary damages resulting in whole or part from any user's use of or reliance upon this material.

This site uses cookies to store information on your computer. More info...

hosted on vmrix.com