Simply because it increases the alveolar oxygen pressure (A) without causing a corresponding increase in the arterial oxygen pressure (a) . In case of pulmonary edema gas exchange is impaired in the affected alveoli & intrapulmonary shunt of blood takes place towards the intact ones . The shunted blood doesn't get adequate oxygenation by the intact alveoli even with supplemental oxygen !

Sorry man, it was 10 years, 2 homes, and 3 computers ago. My notes from this era of videos are long gone. If I had to guess, one of the primary references was probably Marino's The ICU Book, supplemented with papers from the primary literature. These days though, there are better resources than Marino (no disrespect!). derangedphysiology.com is a wonderful resource to better understand respiratory physiology and pathophysiology.

@@StrongMed actual mvp! Thanks doctor!

In my experience, it takes less than 5 minutes. However, I have heard others cite 10-15 min (or more) as the length of time to wait after changing FiO2 before rechecking an ABG - which seems excessive to me unless they believe it takes that long to manifest the increased physiologic intrapulmonary shunting caused by high FiO2. To the best of my knowledge, the time course for this process hasn't been well measured.