Use of artificial humidification during non-invasive mechanical ventilation in patients with acute respiratory failure: a narrative review.

Background and Objective: The use of humidification devices has been recommended during non-invasive mechanical ventilation (NIMV). However, existing recommendations on this topic remain limited and inconsistent. The objective of this narrative review is to summarize the current state of knowledge regarding the need for and timing of humidification during NIMV. Methods: A bibliographic review of the literature published over the last 30 years (time frame chosen arbitrarily) was conducted using the PubMed database to identify relevant studies addressing the role of humidification in NIMV, with a particular focus on clinical guidelines and expert consensus statements. Key Content and Findings: NIMV may induce undesirable physiological and histological effects, leading to patient discomfort and reduced tolerance, which can ultimately contribute to NIMV failure. For these reasons, most guidelines and experts recommend the use of humidification during NIMV. However, there is no consensus regarding the optimal timing for initiating humidification in the acute setting. The decision to apply humidification may depend on several factors, including the expected duration of NIMV, the underlying clinical diagnosis, and patient-reported symptoms. Overall, based primarily on physiological evidence, the literature suggests that heated humidifiers (HHs) may be superior to heat and moisture exchangers (HMEs). Nevertheless, this potential advantage of HH over HME is not consistently supported when clinical outcomes are considered. Conclusions: Current guidelines and expert recommendations generally advocate the use of additional humidification during NIMV, given the low humidity of inspired air in its absence and the possible adverse effects on upper airway function, patient comfort, and tolerance. However, further studies are needed to clarify the necessity of humidification during the acute phase of NIMV. While physiological data favor HH over HME, this superiority is less evident when clinical endpoints are evaluated. More real-world studies are warranted to determine the actual comparative benefits of each humidification method.