"Today we're talking about a hack to estimate what the patient's PAO2 or the arterial oxygen should be on your blood guess based on the FAO2 that they're receiving. So quick disclaimer, to do this you need to assume that the patient has no VQ mismatch, no shunt, no diffusion problems, basically perfect lungs, and in an ICU patient that hardly ever happens. But stick with me for a second. Take someone who's at C level breathing regular oral oxygen, 21%, we'll just say 20 for this math here, 20 times 5 should get you to a PO2 of 100. That's what the blood guess you expect to be if you did an ABG on a normal person would be. Now if you're taking a person on a ventilator and they are just intubated and their FAO2 is 100%, 100 times 5 is 500, so your expected PO2 should be 500. If they're on 60% option, it's 60 times 5, it should be 300. And although this is just an estimate, it's important to have an expectation when you send a blood guess as to what that PO2 is going to be. So it's very important that you know the FAO2 that that patient was on when you sent that blood guess off, because when that blood guess comes back, you have to know what the expected normal is, and then see if there's any discrepancy to understand how bad that person's disease is. Have you ever heard this hack before? Let me know in the comments below."