When a patient breathes through the nose, the inspired air
is warmed to body temperature and becomes saturated with
water vapour before entering the trachea.
Therefore it is important to humidify medical gases due to the following reasons:-
Medical gases have very low moisture content and, delivered via endotracheal
tube or tracheostomy, cool and dry the lower airway. Mucus becomes thicker (‘plugging’ airways). The airway epithelium becomes desiccated, causing ciliary mucus transport to fail, and thence epithelial denudation. The risk of atelectasis, lobar collapse and infection then rises.
Ref; Intensive Care Foundation, 2015