I have lectured extensively, on the podcast and in person, on the necessity of a PEEP valve to make a BVM work properly. It is part of the Ultimate BVM and allows for Apneic CPAP (you know the technique that would have made apneic ox actually work in the sick patients in the Fellow Trial). You can find extensive discussion of Apneic CPAP and why you need a nasal cannula to turn the BVM/PEEP Valve from low-flow CPAP to high-flow CPAP (you want high-flow CPAP) on the EMCrit PreOx Page. You can see the EMCrit video on this concept of Apneic CPAP from 2011.
Friend to the show, George Kovacs, demonstrates these concepts beautifully and succinctly in the above cadaver video.
I will repeat what I have said at every recent airway lecture: BVM + PEEP Valve + NC represents the ultimate PreOX, ApOx, and ReOx device currently available