PF Ratio Versus FR2?

The tidal volume on the ventiator is something which you can monitor by looking at the X-pitalal volume. If it's above 9.5 millilitre per kilogram, there is a very high chance that the patient will fail. How does the PF ratio play in the ratio of the PO2 versus the FR2? So let's say if we look at the epidemiological studies which look at hypoxemic patients treated with noninvasive ventilation. People have used the same category of ARDS like mild-moderates severe which would mean a PF ratio below 300 or below 200 or below 100.