Retention of airway secretions is highly common in critically ill patients, on mechanical ventilation (MV). The
endotracheal tube (ETT) plays a critical role in this context; indeed, upon inflation of the ETT cuff, mucociliary transport
drastically impairs. Additionally, patients with neurological impairments or underlying diseases, i.e. asthma, chronic
obstructive pulmonary disease, cystic fibrosis and non-cystic fibrosis bronchiectasis are at the greatest risk. Indeed, in
these patients, MV rapidly disrupts the balance between overproduction of mucus and impaired clearance capabilities.
Importantly, during MV, mechanically ventilated patients are positioned in the semi recumbent position and several
laboratory studies suggested that in this position retained mucus might move toward the distal airways, driven by gravity.
Additionally, airflow promotes clearance or retention of retained mucus, via a two-phase gas-liquid flow mechanism. In
sedated, invasively ventilated patients, the inspiratory flow can be modulated through the ventilatory settings, and
theoretically, mucus clearance could be promoted or hindered through adjustments of the ventilatory settings. Yet, these
assumptions should be corroborated in large translational clinical trials. Importantly, humidification of respiratory gases
plays an essential role in maintaining mucus clearance rate within the physiologic range. Thus, the most appropriate
humidifier should be chosen on a case-by-case basis, and given the reported poor performance of heat-moisture exchanger
during ventilation at high minute volumes, heated humidifiers should be a primary choice for patients requiring high
ventilatory support. Finally, numerous drugs, commonly used in ventilated patients, i.e. oxygen, inhaled anesthetics,
narcotics profoundly affect mucociliary clearance and increase mucus retention.