Dear. Dr. Nashwa,
In our unit, oxygen blender is out of reach, it's too expensive.. We use this formula to lower our oxygen concentration. V1 is volume of the first gas (oxygen), times M1 (which is oxygen concentration of the first gas, central O2=100%).. Added to V2 (volume of the 2nd gas, which is air), times M2 (21%).. Equal to V3 (volume of the 3rd gas), times M3 (the new concentration).
For example : 1 L O2 100% + 6 L Air (21%) = 7 L. M3 (new gas)
So the equation becomes : 1.100 + 6.21 = 7.M3
100 + 126 = 7.M3
So M3 (the new gas concentration) is 226/7 = 32.3%
This is how we lower our oxygen, so the baby would not receive 100%..