Normal adult airway.
The respiratory system is a highly balanced mechanism reliant on humidity.[4] During normal inspiration, as air travels down the airway heat and moisture are drawn from the airway mucosa until the gas reaches 37 °C, 44 mg/L H₂O close to the carina.[5,6]
Bypassed airways.
When the upper airway is bypassed, e.g., with a tracheostomy tube, the upper airway’s humidifying surfaces and filtering mechanisms are also bypassed. This compromises the protective cough, gag and sneeze reflexes.[7]
Complications associated with the failure to heat and humidify inspired gases for patients with bypassed airways include thickening of secretions, drying of the airway, airway obstruction (including blockage of artificial airways) and bronchospasm.[8]
Secretion clearance for efficient gas exchange and ventilation.
Secretion clearance is fundamental to limiting airway occlusion and promoting efficient ventilation and gas exchange. Humidification is integral to secretion management in mechanically ventilated patients [8] and it assists with secretion mobilization and removal.[3,9] Insufficient respiratory humidification can result in diminished cilia activity, decreased cilia beat frequency, ciliary destruction and cellular damage.[4] This can lead to increased mucus viscosity and impaired mucociliary clearance, which can cause secretion retention, with potential for airway occlusion and atelectasis.[4]
Supporting the natural defense mechanisms in the airway.
It is important for the airway mucosa to retain a balance of heat and moisture to maintain a fully functioning mucociliary transport system and an efficient line of defense. When mucus transport is inadequate, mucus can turn into a risk factor instead of a defense mechanism. Therefore, humidification and as-needed suctioning are the foundations of secretion management in mechanically ventilated patients.[8] Heated respiratory humidifiers can deliver a higher level of heat and humidity than heat and moisture exchangers (HMEs). Accordingly, they are the humidification method of choice for some patients.[3,8]
Persistent airway inflammation and mucus retention are also clinical problems in patients with chronic respiratory diseases, such as obstructive pulmonary disease and bronchiectasis. Homecare patients commonly use home ventilators where humidity can be used to improve secretion clearance.[10,11]
