Oxygen administration?

Question

the air we breathe is 21% oxygen, 78% nitrogen and 1% other gasses. so why are people given 100% oxygen during medical emergencies?

Answer 1

Because the need for oxygen is greater.  There may be problems with oxygen delivery (with asthma, for example) or with tissues needing all the oxygen they can get (heart muscle during a heart attack).

Many times, patients are not given 100% oxygen.  Nasal cannula and most face masks provide less than 100%.  You need a non-rebreather face mask (or endotracheal tube) to give 100% O2)