Fraction of Inspired Oxygen (FiO2)

For all supplemental oxygen delivery devices, the patient is not just breathing the direct oxygen, but rather is breathing a combination of room air plus the oxygen from the supplemental device. Different devices deliver to the patient more or less of a % of what is coming in from the tank.

Fraction of Inspired Oxygen (FiO2) for a nasal canula and a Venturi mask are given in the tables below. For other oxygen delivery systems, such as masks, tents, there is more oxygen that "blows by" or is lost, therefore higher flow rate setting on the oxygen tank are needed to achieve the same FiO2.
A tracheostomy would require different calculations as well.

Example:
with a nasal cannula, we assume that the fraction of oxygen that is inspired (above the normal atmospheric level or 20%) increases by 4% for every additional liter of oxygen flow administered.

For a Nasal Cannula:

Oxygen tank FLOW RATE in liters / min FiO2 -- Fraction of Inspired Oxygen value
0 (no oxygen, just room air) .20
1 L / min .24
2 L / min .28
3 L / min .32
4 L / min .36
5 L / min .40
6 L / min .44


For a Venturi Mask:

Oxygen tank FLOW RATE in liters / min FiO2 -- Fraction of Inspired Oxygen value
0 (no oxygen, just room air) .20
4 L / min .24 - .28
6 L / min .31
8 L / min .35-40