Oxygen Requirement Calculator

Room air has an FiO2 of approximately 21%.

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.

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.

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.

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.

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.

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