What is the maximum fraction of inspired oxygen (FiO2) that can be delivered via a nasal cannula?

From the Guidelines

The maximum FiO2 that can be delivered via a standard nasal cannula is approximately 40-50% when set at a flow rate of 6 liters per minute, as indicated by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.

Key Considerations

• The actual concentration of oxygen delivered (FiO2) cannot be predicted and varies with patient breathing patterns, but generally increases with flow rate up to 6 L/min 1.
• For each liter of oxygen flow through a nasal cannula, the FiO2 increases by about 4% above room air (21%), so 1 L/min provides roughly 25% FiO2, 2 L/min provides 29%, and so on up to 6 L/min 1.
• Patient discomfort and nasal dryness may occur at flows above 4 L/min, but can be tolerated by some patients 1.
• If a patient requires higher oxygen concentrations, alternative oxygen delivery devices should be considered, such as a simple face mask (which can deliver 35-50% FiO2), a non-rebreather mask (60-80% FiO2), or high-flow nasal cannula systems which can deliver up to 100% FiO2 with flows of 60 L/min or more.

Clinical Implications

• The choice of oxygen delivery device should be based on the patient's individual needs and tolerance, as well as the required FiO2 1.
• Regular monitoring of oxygen saturation and adjustment of the oxygen flow rate as needed is crucial to ensure adequate oxygenation and minimize the risk of hyperoxia or hypoxia 1.
• The BTS guideline for oxygen use in adults in healthcare and emergency settings provides a comprehensive framework for oxygen therapy, including the use of nasal cannulas and other oxygen delivery devices 1.

From the Research

Maximum Fraction of Inspired Oxygen (FiO2) via Nasal Cannula

• The maximum fraction of inspired oxygen (FiO2) that can be delivered via a nasal cannula is a crucial aspect of oxygen therapy, and several studies have investigated this topic 2, 3.
• According to a study published in 2014, the FiO2 delivered by nasal cannulae increased by 0.038/L/min of oxygen, and a normal respiratory rate of 15 breaths/min with oxygen supplementation via nasal cannula at 2 L/min resulted in an FiO2 of 0.296 2.
• Another study published in 2021 found that the actual FiO2 is never as high in spontaneously breathing patients as that estimated, and that tidal volume (VT) and oxygen flow rate are the principal factors influencing measured FiO2 3.
• However, the maximum FiO2 that can be delivered via a nasal cannula is not explicitly stated in these studies, and it is likely that the maximum FiO2 will vary depending on the specific nasal cannula device and the patient's individual characteristics.

Factors Influencing FiO2 Delivery

• Several factors can influence the FiO2 delivered by a nasal cannula, including:
  • Respiratory rate: an increase in respiratory rate can decrease the FiO2 2, 3.
  • Tidal volume (VT): an increase in VT can decrease the FiO2 3.
  • Oxygen flow rate: an increase in oxygen flow rate can increase the FiO2 2, 3.
  • Mouth position: the FiO2 can decrease with the mouth open 2.
  • Estimated minute ventilation (VE): the FiO2 and PA O2 can decrease with increasing VE 2.

Clinical Practice and Guidelines

• The use of nasal cannulae for oxygen therapy is common in clinical practice, and several studies have investigated the clinical practice and guidelines for their use 4, 5, 6.
• However, the maximum FiO2 that can be delivered via a nasal cannula is not explicitly stated in these studies, and it is likely that the maximum FiO2 will vary depending on the specific nasal cannula device and the patient's individual characteristics.