Oxygen Therapy Guidelines

Estimating FiO2 with Nasal Cannula

With a nasal cannula, each liter per minute of oxygen flow increases the inspired oxygen concentration (FiO2) by approximately 3-4%, starting from 21% of ambient air 1
The estimated FiO2 with nasal cannula at different flow rates is as follows:

The actual FiO2 delivered cannot be predicted with precision because it depends on multiple patient variables 1
Patients with high respiratory frequency receive less FiO2 with the same flow 1
Mouth breathing reduces FiO2 by an average of 2.4% 1

The Venturi mask is approximately twice as efficient as the nasal cannula 3
The Venturi mask provides precise and controlled FiO2, maintaining constant concentrations regardless of the patient's respiratory pattern 3

The Venturi mask system provides the following FiO2 concentrations:
The Venturi mask is especially recommended for patients with COPD or at risk of hypercapnic respiratory failure who require precise oxygen control 4, 3

Simple mask: 5-10 L/min provides 40-60% FiO2, and should never be used below 5 L/min due to the risk of CO2 reinhalation 2
High-flow nasal cannula (HFNC): 30-70 L/min provides more predictable FiO2 and a modest CPAP effect 2

Nasal cannula at 8 L/min is near the upper limit of comfortable flows, as some patients experience discomfort and nasal dryness with flows above 4 L/min 1
For patients with acute COPD exacerbation, do not administer FiO2 greater than 28% via Venturi mask or 2 L/min via nasal cannula until arterial blood gases are known, with a target saturation of 88-92% 4, 3
Oxygen titration should be based on oxygen saturation measurements, not theoretical estimates of FiO2, especially with nasal cannula where actual FiO2 varies significantly 1, 2