You know sir, it's such an easy calculation when you're explaining it, but I couldn't figure it out for the life of me while standing at the head of the bed last week. Thanks a bunch for the video!
What if you had the FiO2 and total flow between 2 gases but needed to find the individual flow of each gas ? I was trying to work it backwards but can’t figure it out !! Thanks !!
Say the flow of gas 1 is f1 and gas 2 is f2. Also say the fraction of o2 in gas 1 is x1 and in gas 2 is x2 (I.e. x of pure o2 would be 1 and of air would be 0.21) Say the total flow (which is known) is f_tot = f1 + f2 FiO2 = (f1*x1 + f2*x2) / f_tot So: FiO2 * f_tot = f1*x1 + f2*x2, with the left side being known in value You can then use f1 = f_tot - f2 and f2 = f_tot - f1 to get the right hand side to a single variable and solve it. For example for f1 it would be: FiO2 * f_tot = f1*x1 + (f_tot - f1)*x2 If you rearrange for f1 you get: f1 = (f_tot * (FiO2 - x2)) / (x1 - x2) Then you get f2 from f2 = f_tot - f1 Hope this helps!
