FiO₂ and oxygen-delivery devices

• Identify the device actually connected to the patient.
• Check the set flow, system seal and the patient's condition.
• Remember that nasal cannulae, simple masks and reservoir masks provide estimated FiO₂ values.

With Venturi masks, HFNC and anaesthetic circuits, the value is controlled by the device. Always verify the local protocol.

• Nasal cannula: 1 L/min ≈ 24%, 2 ≈ 28%, 3 ≈ 32%, 4 ≈ 36%, 5 ≈ 40%, 6 ≈ 44%.
• Do not set a simple mask below 5 L/min.
• Simple mask: 5 L/min ≈ 40%, 6 ≈ 50%, up to 10 L/min ≈ 70%.

These are estimates: respiratory rate and tidal volume affect the FiO₂ actually inspired.

• Venturi: check the colour and jet specified by the manufacturer before connecting the flow.
• Reservoir: verify that the bag remains inflated throughout inspiration.
• Non-rebreather with valves and an inflated reservoir: approximately 60–95% at 10–15 L/min.
• Partial rebreather: approximately 50–70% at 6–10 L/min.

Venturi colours may vary between manufacturers. Always read the device labelling.

• HFNC: FiO₂ is set directly on the device, from 21% to 100%.
• Bag-valve mask without an oxygen source: 21%.
• Bag-valve mask with oxygen and inflated reservoir: approximately 90–100%.
• Anaesthetic circuit: confirm the actual FiO₂ setting on the gas mixer.