How to Use the PF Ratio in a Patient's ABG

The PAO2 is important for switching oxygen and CO2 over the AC membrane. If you have a chronic VQ mismatch, like COPD or maybe interstitial lung disease, that totally screws it up. It doesn't account for any altitude. But also if you look at the A to A gradient, which is by the way, it gets the difference between the oxygen pressure and your LVO in the blood, P big AO2 minus P little AO2. That's just a subtraction. You don't even really need a PF ratio for that. Like if you're at 100% oxygen and then your PAo2 is less than 100, I mean, you're