ELI5: How does inert gas asphyxiation really work? Recent episode of Dr. Mike reviewing \*The Pitt\* and a scene rebreathing with a paper bag brought this question back to mind. So, the conventional wisdom is that the human body doesn’t detect low O2 levels, but rather high CO2 levels as a result of acidification of the blood; this is what causes all the panicked, gasping reflexes. As a consequence, you could breathe in 100% nitrogenous air and lose consciousness in seconds without ever really realizing what’s happening — no pain or fear. Fighter pilots train in low-oxygen environments precisely because it can make you delirious in seconds, and dead shortly thereafter. On the other hand, the world record for longest breath held is just shy of 30 minutes, which is absolutely insane. I’m aware that we do exhale the majority of the oxygen which we breathe in, but it still seems like a very big disparity to make up between “unconscious in seconds” and a half hour without breathing.…