Formula For Air/o2, No2/o2 Mixtures

Hi guys,

Hope someone can help me with this question.

Does anyone know how to manually calculate (if there's a formula) the percentage of gases, especially room air and oxygen or roomair, oxygen & NO2, that the patient is getting through the anesthesia machine? Without looking at the monitor's inhaled oxygen, air, or NO2 readings?

Especially when someone asks, "Give the patient 33 percent FI02 of air/02 mixture". How do you guys figure out where to set the air flow meter and 02 flow meter without looking at the monitors?

Does my question make sense? Sorry, I just woke up.

Thanks!