Nasal cannulae are only capable of delivering an inspired oxygen concentration between 24% and 40%.

For any given flow rate, the inspired oxygen concentration will vary between breaths, as it depends upon the rate and depth of the patients breath and the inspiratory flow rate.

Higher rates can cause nasal mucosal drying and may lead to epistaxis.

If oxygen is administered at greater than 40% it should be humidified. You cannot humidify oxygen via nasal cannulae