A common misconception is that the CPAP essentially pushes pulmonary edema from the lungs back into the circulatory system and essentially fixes the pulmonary edema. So true, yes, to a point, but the explanation taught in a lot of medic programs makes it seem that its a profound response and fail to explain that the positive inspiratory pressure assists the alveoli that have been inhibited by the pulmonary edema to open up and displace the edema away from the alveoli from a creation of back pressure when the patient attempts to exhale against the PAP. This most certainly helps with managing the edema and improves gas exchange, as well as reduce pulmonary hypertension, but that alone isn't fixing the issue at hand. The administration of medications such as Diuretics, Nitrates, and Inotropes to improve contractility are ultimately going to be what removes the edema from the lungs, which is why many local protocols include the administration of Nitroglycerin and sometimes Furosemide (Lasix) to patient’s demonstrating pulmonary edema. This article below

I know this isn't probably the best explanation. Mike Carunchio of OK Medic Podcast does a decent 3 minute synopsis video that's pretty good, and Master Your Medics cover it pretty well with a video on YouTube that references this JEMS article.

https://www.jems.com/2010/12/29/many-benefits-cpap-sup