USE of PF Ratio with ARDS

Just curious. I am taking a critical care class at my hospital and we were discussing today some of the clinical indicators of ARDS. One of the things that was mentioned is the PF ratio, where you take the Pa02 from an ABG and divide it by the pts Fio2 and put it in a decimal format. This gives you a number of how much of a shunt a patient has who is not ventilating or perfusing adequately.

A PF of 286 or greater indicates "normal" ventilation, and I was told if a patients PF was less than 286, the patient should not be extubated. If a patient has a PF of less than 200, this is classified as ARDS, and measures to improve lung function/ventilation should be instituted quickly- such as rotation bed, percussion, different vent modes.

We haven't made this an official assessment at my hospital yet, but some of the CCRNs, educator, and other experienced ICU RNs are pushing that we should use it. If it is an accurate indicator of ARDS, I think it would be beneficial to "catch" pts who have pulmonary compromise and are headed towards ARDS early on instead of waiting until it is full blown and crossing your fingers that the pt will get over the insult to the lungs.

Does anyone else use this in their units? If so, what is the outcome for patients who have a low PF with ARDS? We are getting more and more ARDS pts in my unit, so I thought this was very interesting.

The number you mention (PF) can be 'bad' in many other lung conditions...(cardiogenic pulmonary edema(CHF), pneumonia, pneumothorax,COPD, etc...) So you really can't diagnose ARDS by using this number in isolation. Good old fashioned CXR's and pt History can better diagnose an ARDS.

And by the time this PF number becomes 'BAD', the patient is already in ARDS so it wouldn't be a valuable tool in 'catching' ARDS before it occurs.

Also, it's not neccesary(sp?) to calculate a PF prior to extubation. If the pt's PF is bad, the ABG's will reflect this (and without having to do all the calculus :) ) .

Gosh golly I haven't seen this one in a while!

I was taught this in my critical care internship in 1997. I saw it used there (a level 1 trauma major teaching institution- GREAT hospital) and at one small hospital by one pulmonologist (really good hospital, fantastic doc.) I've worked at many other hospitals that were good and not so good and have only seen it at those two.

I agree with the other poster- there is no one universal good or bad number, there is no one factor that says you do or do not have ARDS, and by the time you get below that 200 threshold you're already there.

But it is a good concept to know and it will never hurt your patient to watch the trend. It will never be the only "should we extubate or not" factor but it's a good thing to understand.

Remember that there is no "magic number". A number just represents a snapshot in time. The best thing to look at are trends as this will give you the best picture of what is going on with your patient.

Here is the ARDSnet protcol: NHLBI ARDS Network

,Tahoma]

If a patient has the following we ventilate as per the ARDSnet Protocol