The P/F ratio is a quick calculation you can do that will help you and the medical team determine if the patient has ARDS (acute respiratory distress syndrome).

First, find your PaO2 from your blood gas and the FIO2 on your ventilator (or from whatever oxygen delivery device you are using). For this example, let’s say your PaO2 is 83 and your ventilator is set at 45% FIO2.

Next, convert your FIO2 into a decimal…in this case it is 0.45

Then, just simply divide your PaO2 by the FIO2…it will look like this: 83/0.45 = 184.

Anything less than 300 is indicative of ARDS…but what about levels of severity? Glad you asked!

  • 300 to 200 is considered mild ARDS
  • 200 to 100 is considered moderate ARDS
  • Anything below 100 is considered severe ARDS.

Of course, you never just go by numbers alone. Always look at your patient and take in the whole picture (suddenness of onset, chest x-ray, etc….).

In another post, we’ll look at the alveolar-arterial gradient and then you’ll really be feeling confident in the ICU. You’ve got this!

____________________________________________________________

The information, including but not limited to, audio, video, text, and graphics contained on this website are for educational purposes only. No content on this website is intended to guide nursing practice and does not supersede any individual healthcare provider’s scope of practice or any nursing school curriculum. Additionally, no content on this website is intended to be a substitute for professional medical advice, diagnosis or treatment.


Are you a nursing or pre-nursing student? Then you are probably searching for ways to make your life more joyful and less stressful. It all starts right here…with the Straight A Nursing Planner, the first planner ever designed specifically for nursing students. Click on the link below to learn more.

Get organized for nursing school with the Straight A Nursing planner