Oxygen Requirement Calculator
Estimate FiO2 based on supplemental oxygen flow rate and delivery device. Nasal cannula adds roughly 4% per L/min above 21% room air. Simple masks deliver 35-50% FiO2, while non-rebreather masks provide 60-90% FiO2 depending on flow.
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Formula
A common rule of thumb for patients on nasal cannula: each Liter/min of flow increases the FiO2 by approximately 4%.
Worked Example
Understanding FiO2 by Delivery Device
- Nasal cannula (1-6 L/min): approximately 24-44% FiO2, adding roughly 4% per L/min above room air
- Simple face mask (5-10 L/min): delivers 35-50% FiO2
- Non-rebreather mask (10-15 L/min): delivers 60-90% FiO2 using a reservoir bag
- Venturi mask: precise FiO2 delivery (24-60%) using calibrated entrainment ports
- High-flow nasal cannula (HFNC) can deliver up to 100% FiO2 at flows of 40-60 L/min
These values are estimates. Actual delivered FiO2 varies with the patient's respiratory rate, tidal volume, and breathing pattern. Venturi masks are preferred when precise FiO2 control is required.
You can also calculate changes using our A-a Gradient Calculator or PaO2/FiO2 Ratio Calculator.
Frequently Asked Questions
What is room air FiO2?
Room air has an FiO2 of approximately 21%.
Is the 4% rule exact?
No, it is an estimate. Actual FiO2 varies with the patient's respiratory rate and tidal volume. At higher breathing rates, the effective FiO2 may be lower because more room air is entrained.
When should I use a Venturi mask?
Venturi masks provide a more precise and guaranteed FiO2 (24-60%), which is important for patients with COPD who require strict oxygen control to avoid suppressing their hypoxic drive.
What FiO2 does a nasal cannula deliver at 4 L/min?
Using the estimation formula (21% + 4% per liter), 4 L/min via nasal cannula delivers approximately 37% FiO2. Nasal cannula is generally used from 1 to 6 L/min.
What is the difference between a simple mask and a non-rebreather?
A simple mask delivers 35-50% FiO2 at 5-10 L/min. A non-rebreather mask has a reservoir bag and one-way valves, delivering 60-90% FiO2 at 10-15 L/min for patients needing high-concentration oxygen.
Why is estimating FiO2 important clinically?
Knowing the FiO2 is essential for calculating the P/F ratio (PaO2/FiO2) and A-a gradient, both of which help assess the severity of respiratory failure and guide treatment decisions.
Medical Disclaimer
This calculator is provided for informational and educational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any decisions based on these results. Do not disregard or delay seeking medical advice because of information obtained from this tool.
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Our AI assistant provides general estimates and advice only. Please consult a qualified healthcare professional before making any health-related decisions.
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