There have been years of attempts at creating an artificial blood O2 and CO2 carrier but so far nothing really viable has seemed to come out. In the mean time they're just slowing down the chemical processes that cause so much damage to the brain in the absence of oxygen.

Seems like a combination approach might help. Even if a carrier isn't good enough at body temperature, it might extend viability when chilled, compared to just using saline.

Wonder how feasible it'd be to er... super saturate "stock" blood (eg from blood packs) with extra oxygen carrying red blood cells? Preferably oxygenated just prior to being used for this.

Doesn't really help if the path to the brain is leaking like a sieve. Also one of the goals with blood substitutes was to make them physically smaller than red blood cells to get past the second issue which is swelling that can restrict blood supplies. The idea was a smaller O2 carrying molecule could squeeze through where a red blood cell couldn't.