According to all the sources it is allowed to give oxygen with nasal cannula from 1 to 6 liters per minute, not more, to avoid damaging of the mucosa, and if you deliver oxygen generally at a rate more than 4 liters per minute you are supposed to humidify to avoid dryness of the mucosa. so my question is why it is not allowed to give oxygen with a nasal canulla at a rate more than 6 liters per minute if it is humidified?