Hypoxia is a medical condition in which the cells of a living organism are deprived of oxygen.
Cervantes Quinn used a medical tricorder in 2268 on himself and discovered that he was suffering from hypothermia and hypoxia. He was able to cure the hypothermia with some tri-ox compound. (VAN - Declassified novella: The Stars Look Down)
Starfleet officers were trained how to combat hypoxia in low-oxygen environments. Sonya Gomez used these techniques while trapped aboard Recreational Station Hidalgo in 2376. (SCE eBook: Identity Crisis)