Certainly not the same situation but ~7 years ago my FIL had a massive heart attack with my wife and MIL present and from that very very long night I remember how important those minutes are. MIL administered CPR and, very luckily and somewhat coincidentally, they happened to be in a neighborhood very close to an ambulance station.Do you mean because that's supposedly (or actually, don't know if it was confirmed) how long the CPR was? That's actually the whole point of CPR is you press on the chest and basically squish the heart so that it pumps blood throughout the body, for really the sole purpose of getting oxygen to all the organs. So while it definitely wasn't ideal levels of oxygenation, his brain was definitely getting something during that time. (And if I misunderstood you or there's information I don't have, my apologies!)
He was intubated and Doc gave us what sounded like a very bad prognosis (plans to induce hypothermia) based on not being certain how long he may have been oxygen-deprived for, but by night’s end he was showing clear signs of brain function and he was in the clear to be moved for bypass surgery the next day.