Why is the O in N₂O not accessible, thus resulting in hypoxia? If you blow nitrous oxide through a lit cigarette the resulting increased burn it says there's more oxygen, not a lack of it.
Same reason the O in CO2 isn't accessible. Oxygen is used as an oxidizer in the slow burn that is human respiration. N2O is already "burnt", so your body can't burn it any further to release energy.
I believe nitrous oxide can act as an oxidizer, but cannot be used for respiration for a different reason than CO2 (already fully oxidized). But I'm not sure what that reason is: maybe the enzymatic capacity to pull the O off the N2 is just order(s) of magnitude too small or it has to go through NO metabolism.
