Airway hydration homeostasis in artificial airways: from mucus biophysics to monitoring and humidification strategies in critical care: a narrative review.

Artificial airway placement bypasses the physiological warming and humidifying functions of the upper airway. This produces a distal shift of the isothermic saturation boundary and exposes the tracheobronchial mucosa to additional evaporative stress. When inspired gas is inadequately conditioned, the resulting evaporative stress can deplete airway surface liquid, concentrate mucus, impair mucociliary clearance, and promote secretion retention and mucus plugging. Airway hydration imbalance is not simply a problem of insufficient water delivery. Rather, it reflects a dynamic interaction among gas thermodynamics, epithelial ion transport, mucin network organization, inflammatory burden, secretion biophysics, and ventilator-patient conditions. Current humidification strategies, mainly heated humidifiers and heat-and-moisture exchangers, provide essential support during invasive and non-invasive ventilation. However, their performance is often constrained by open-loop operation, device-related limitations, and heterogeneous patient requirements. This review summarizes the physiological basis of airway hydration, the mechanisms by which artificial airways disturb hydration homeostasis, clinical assessment approaches, and current humidification strategies. It also discusses newer approaches, including ventilator waveform-derived indices, microrheological assays, artificial cilia sensors, microfluidic platforms, and closed-loop humidification frameworks. Future studies should determine whether integrating patient characteristics, secretion properties, ventilatory conditions, and device performance can support more individualized humidification strategies. Technologies that remain at the model or prototype stage should be interpreted cautiously.