Fraction of Inspired Oxygen (FiO2)

Related article: Oxygen Delivery Methods

I just spoke with a respiratory therapist who taught me the following rules for estimating FiO2. I verified and the information is true.

For a patient on NC, to determine the FiO2, you multiply the number of liters by 4% and then add to 20% (which is an estimate of the % of oxygen in room air)

E.g. I had a pt on 4L NC.  1L=4%, 4 x 4% = 16%. The FiO2 for my patient is 16 +20 = 36%

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.

The Fraction of Inspired Oxygen (FiO2) for a nasal cannula 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:

For a Venturi Mask: