Overview
Low flow oxygen devices deliver an amount of gas that is less than the patient's total minute ventilation.
The oxygen from the circuit is passively mixed with room air as the patient inspires, resulting in a variable FiO2 that depends on many factors including the respiratory rate, tidal volume and whether the patient is breathing through their nose or mouth.
Nasal Prongs
Low flow nasal prongs deliver 100% oxygen at a low flow rate, which is then entrained with room air. Nasal prongs are comfortable and allow the patient to eat, however at flow rates higher than 4 L/min can cause drying of the nasal cavity.
| Flow | FiO₂ |
| 1 L/min | ~0.24 |
| 2 L/min | ~0.28 |
| 3 L/min | ~0.32 |
| 4 L/min | ~0.36 |
Simple Face Mask
A simple face mask, also known as a Hudson mask, allows a larger amount of oxygen to be entrained with room air. As they have no reservoir bag, the maximum FiO2 possible is around 0.60.
The flow into a Hudson mask should be at least 5 L/min, to reduce rebreathing of carbon dioxide.
| Flow | FiO₂ |
| 5 L/min | ~0.36 |
| 6 L/min | ~0.42 |
| 7 L/min | ~0.48 |
| 8 L/min | ~0.54 |
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