What is the air-O2 ratio formula when two LVNs or mixtures of air and oxygen are combined?

The formula that determines the air-O2 ratio when mixing air and oxygen involves evaluating the fraction of inspired oxygen (FIO2) and understanding how it relates to the concentrations of the individual gases. The correct answer effectively captures the relationship between the FIO2 of the mixture, the atmospheric oxygen concentration at sea level (which is generally considered to be 21% or 0.21), and the required ratios of air versus oxygen needed to achieve that specific FIO2.

When using the formula 100 - FIO2 / FIO2 - 21, it provides a systematic way to calculate how much air is needed relative to the oxygen to achieve a desired FIO2 in a gas mixture. This formula directly accounts for the oxygen percentage in the atmosphere (21%) as a baseline, allowing practitioners to calculate how far off their target is from room air and how much supplemental oxygen is required.

When combining different proportions of air and oxygen, this formula allows for adjustments to achieve precise concentrations necessary for optimal patient care in respiratory therapy. It is fundamental for understanding and applying therapeutic interventions effectively. The use of FIO2 in this formula reflects a common practice in respiratory care, making it essential for those training in this field.