Enter the PAO2 and the PaO2 into the Calculator. The calculator will evaluate the A/A Ratio. 

A/A Ratio Formula

A/A = PAO2 / PaO2

Variables:

  • A/A is the A/A Ratio ()
  • PAO2 is the PAO2
  • PaO2 is the PaO2

To calculate A/A Ratio, divide the PAO2 by the PAO2.

How to Calculate A/A Ratio?

The following steps outline how to calculate the A/A Ratio.

  1. First, determine the PAO2. 
  2. Next, determine the PaO2. 
  3. Next, gather the formula from above = A/A = PAO2 – PaO2.
  4. Finally, calculate the A/A Ratio.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

PAO2 = 15

PaO2 = 19

FAQs

What is the significance of the A/A Ratio in medical practice?
The A/A Ratio is significant in medical practice as it helps in assessing the efficiency of gas exchange in the lungs. A normal A/A Ratio indicates effective oxygen transfer from the air to the bloodstream, while deviations can signal respiratory or pulmonary issues.

How can variations in PAO2 and PaO2 affect the A/A Ratio?
Variations in PAO2 (the partial pressure of oxygen in alveolar air) and PaO2 (the partial pressure of oxygen in arterial blood) directly affect the A/A Ratio. An increase in the difference between PAO2 and PaO2 can lead to a lower A/A Ratio, indicating potential issues in oxygen transfer efficiency.

Can the A/A Ratio be used to diagnose specific conditions?
While the A/A Ratio itself is not used to diagnose specific conditions, it can be a useful indicator of the overall health of a patient’s respiratory system. Abnormalities in the ratio may prompt further investigation into conditions such as pulmonary embolism, chronic obstructive pulmonary disease (COPD), or acute respiratory distress syndrome (ARDS).

Is the A/A Ratio calculation applicable in all clinical settings?
The A/A Ratio calculation is most relevant in settings where assessment of gas exchange efficiency is necessary, such as in critical care or pulmonary medicine. However, it requires accurate measurement of PAO2 and PaO2, which may not be available in all clinical settings.