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

Introduction

The main function of the respiratory system is to maintain optimal blood levels of O₂ and CO₂. For such purpose, it is necessary that “fresh” air is actively transported from outside the body to the alveoli in a process known as ventilation. During spontaneous breathing, the inspired gases undergo a conditioning process. In this process, the inspired gases are heated and humidified in the upper airways and part of the lower airways before they reach their destination. When ventilation is limited for whatever circumstance, it can be artificially replaced with or supported through mechanical ventilation (MV). The usefulness and effectiveness of MV has been amply demonstrated, and MV has become the therapy of choice for many patients with acute, chronic, or acute-on-chronic hypercapnic respiratory failure of different etiologies. MV can be administered through either invasive mechanical ventilation (IMV) or non-invasive mechanical ventilation (NIMV). IMV is delivered via an orotracheal intubation (OTI) or a tracheostomy, thereby inhibiting contact of the upper airway from the inspired air and preventing physiological conditioning. In this setting, it is essential that physiological gas conditioning is replaced with artificial conditioning (1). Artificial conditioning is delivered through humidifiers, which may be active (after heated humidifier, HH) or passive humidifiers (after heat and moisture exchanger, HME). Although NIMV is administered through interfaces not invading—and not excluding—the upper airways (nasal/oro-nasal masks, primarily), the high air flow rates delivered and their intrinsic leaks contribute to the loss of heat and moisture and inadequate gas conditioning.

The effects of poor gas conditioning result in patient discomfort, poor adherence to ventilation and, ultimately, mechanical ventilation failure. Despite these facts, experts and scientific societies provide inconsistent recommendations regarding the use of mechanical ventilation. To support the aforesaid, we performed review of the literature currently available. In a leading article published in 2009, Ricard & Boyer claimed that clear recommendations have not been provided on the level of additional humidification to be delivered during NIMV or the most effective method or device to be used. Indeed, the authors questioned whether humidification was really necessary (2). The use of additional humidification was questioned based on data from two surveys on the use of humidification during NIMV in intensive care unit (ICU). One of the surveys revealed that humidification was not delivered in 20% of ICUs. The other survey unveiled that no specific protocols were available in 40% of ICUs and humidifiers were not used (3,4). The American Association for Respiratory Care was the first to publish guidelines for humidification during NIMV [2012]. According to these guidelines, as an ‘optional’ recommendation, humidifiers can be used during NIMV to improve adherence and patient comfort. In case of use, HH was recommended over HME (1). In contrast, Esquinas Rodriguez et al. published a narrative clinical review that considered the use of humidification during NIMV ‘essential’. The authors acknowledged the gap of knowledge on the most appropriate timing of starting humidification. However, they suggest considering its use even when short-term ventilation is expected, although a definition for short-term ventilation is not provided (5).

Three years later, Cerpa et al. conducted another narrative literature review and concluded that “there is not sufficient evidence supporting the routine use of humidification during NIMV”. According to the authors, the delivery of humidification relies on multiple factors, such as patient comfort, the expected length of use, or the technical settings used, to name a few. The authors recommend HH when NIMV is expected to be administered for more than 24 hours, using turbine ventilators, single-limb and leak ventilators (6).

One of the most cited guidelines on the use of NIMV in a hospital setting only mentions humidification superficially (in a Suppl.). In this Suppl., the authors acknowledge the lack of evidence regarding the effects of humidification on intubation and mortality rates or the length of hospital stay during NIMV (7). However, the following is stated “we support the routine use of humidification with heated humidifiers during NIMV, with the possible exception of patients who may only need it for a few hours or less, such as patients with cardiogenic pulmonary edema” (7).

The opposite recommendation was provided by the Indian Society of Critical Care Medicine in 2020. A weak 3B recommendation is provided that “routine use of humidification” is not necessary in patients with acute respiratory failure (ARF) receiving NIMV. However, “in patients complaining of airway dryness or dense secretions, humidification can be considered”, using either an HH or an HME (8).

Finally, the Spanish Society of Pulmonology and Thoracic Surgery, jointly with other related Spanish scientific societies, provided some recommendations in 2021 for the management of patients with ARF requiring NIMV, including the pediatric population (9). This consensus statement was based on an initial evaluation of the evidence available and subsequent validation and voting to determine the level of agreement. In accordance with these experts, active humidification devices “should be used” during NIMV “without adding resistance or dead space to the system”. This method is considered beneficial and effective, although only 53% of authors voted for this option (9). Hence, recommendations are not sufficiently consistent, especially in relation to the use or not of humidification during NIMV. There is more consensus on the type of humidifier to be used, with a clear tendency to recommend HH over HME.

This review is aimed at answering two key questions: Is humidification essential in a context of acute or exacerbation of chronic respiratory failure treated with NIMV? If so, what type of humidifier should be used and when? We present this article in accordance with the Narrative Review reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-162/rc).

Methods

To do this, we carried out a bibliographic search using the PubMed database to identify relevant studies on the role of humidification in NIMV. The search strategy is shown in Table 1.

Relevance of humidification

“Humidity” is defined as the concentration of water vapor present in a volume of gas (10). Humidity can be expressed either as absolute humidity (AH) or as the mass of water in a given volume of gas, usually expressed in mg·H₂O/L; or as relative humidity (RH), that is, the amount of water vapour present in a volume of gas as a percentage of the amount of water vapor that is required to fully saturate the same volume of gas at the same temperature and pressure (10).

The inspired air during calm breathing filtrates to progressively be moisturized and heated until reaching an RH of 100% (AH of 44 mg·H₂O/L) and a temperature of 37 °C. These conditions protect alveolar tissue for an adequate gas exchange (11). These values are reached approximately 5 cm below the main carina, between the 3^rd and 5^th bronchial generation, at the so-called limit of isothermal saturation. As much as 75% of the total heat and humidity is delivered as the inspired gas passes through the upper airways (6,12). This explains the lack of gas conditioning in OTI or tracheostomized patients. Poor gas conditioning during IMV may induce undesired effects, including tracheal inflammation, epithelial metaplasia and necrosis, mucosal ulceration, alterations in mucociliary motility, changes in the quality of secretions and alterations in gas exchange. In this setting, adding artificial humidification becomes essential (6,10,13).

Poor gas conditioning is not expected to occur during NIMV, where the upper airways remain intact. However, the positive pressure applied through masks may also negatively affect inspired gas humidification (14,15). There is cumulative evidence that NIMV reduces AH to levels ranging from 4.8 to 12.3 mg·H₂O/L (13,14,16), which are below the 15 mg·H₂O/L established as the lowest value necessary to prevent patient discomfort (15).

Several values have been suggested to cause this situation, including intentional leaks (15), but most frequently unintentional leaks and mouth breathing. Mouth breathing, which primarily occurs during the use of nasal masks, reduces humidity in the upper airway mucosa (14), both during expiration and inspiration. During expiration, mouth breathing has been suggested to reduce the flow passing through the nose, thereby preventing the nasal mucosa from effectively recovering the heat and humidity of the exhaled gas, as it also occurs with HME. As a result, heat and humidity are not recovered during inspiration (5). Inspired air leaks occurring during mouth breathing would increase the air flow delivered by the ventilator in an attempt to compensate for the air leak. The delivery of cool dry air would contribute to poor gas conditioning (16). The AH of inspired air drops with excessive leaks and the patient has a stronger sensation of mouth dryness (5,16).

When the inspiratory positive airway pressure (IPAP) increases, RH decreases. In addition, when IPAP is increased the temperature of inspired air rises, resulting in a lower AH (13). The flow of dry air through the nose itself may affect ventilation, as it increases nasal resistance (17,18) and obstruction. These events can be corrected or palliated by the addition of humidifiers, ultimately improving tolerance (16,19-21).

Due to the aforementioned factors, NIMV may induce undesired effects, including histological changes in the nasal epithelium (22), abnormal ciliary function, mucus secretion or local blood fluX (23), and increased nasal resistance (6,17). These undesired effects cause discomfort and poor tolerance, thereby contributing to NIMV failure (10). Additionally, they can also hamper OTI, if necessary, which is attributed to the dryness of the upper airway mucosa (4). For these reasons, these same authors recommend using a humidifier during NIMV.

Humidification during NIMV in ARF

To the best of our knowledge, limited studies are available comparing the delivery of positive pressure to the upper airways with and without humidification. Lellouche et al. reported a significant difference in the comfort of patients when HH was added, as measured on a 0–10 visual analogue scale (VAS). It is worth noting that, in the study, continuous positive airway pressure (CPAP) was delivered to six healthy subjects for a short time (10 minutes) (15). A communication was presented at the 2013 European Respiratory Society Annual Congress. It was a cross-over study comparing patients with hypercapnic respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD) or patients with hypoventilation obesity syndrome receiving NIMV and alternatively adding and removing humidification. The study revealed no significant differences in patient-reported comfort, as measured on a VAS, eight hours after the initiation of treatment. Interestingly, the group who used HH claimed a higher discomfort due to the temperature of face skin within the masK (24).

Therefore, there is no conclusive evidence about the need for humidification during NIMV. Nevertheless, recommending the delivery of humidification during NIMV seems reasonable, considering the evidence available on the low humidity of inspired air and its potential deleterious effects on the airways and the associated impact on patient comfort and tolerance. This recommendation is logical, especially as these negative effects are known to be corrected with the use of a humidifier. Expert statements and experiences highlight the need to improve patient comfort and tolerance and prevent undesired effects (12,25).

However, some factors should be considered before establishing the need to deliver humidification in this setting. The four studies suggesting that humidification should be added to improve tolerance to NIMV were performed in patients with a diagnosis of obstructive sleep apnea receiving long-term CPAP through a nasal mask with nasal complaints (14,19-21). The setting is considerably different when NIMV is delivered to patients with ARF using oro-nasal masks and dual pressure ventilation methods, or receiving NIMV for other causes. Moreover, CPAP was delivered in one of the studies directly comparing the use of a humidifier during NIMV versus no-humidification, and the setting was very different from ours (15). The other study was never published (24).

The data available are based on physiological factors and do not provide supporting clinical data (mortality, length of hospital stay, ventilation failure rate...), which are essential to decision-making (7). In addition, patients used nasal masks in these studies, which are not the type of mask routinely used in patients with ARF. Martins De Araújo et al. demonstrate that the use of an oro-nasal mask prevents inhaled air dryness in a similar way to an HH (14). Thus, Richards et al. observed that the use of settings replicating closed-mouth breathing, despite differences in air temperature and humidity, prevented changes in airway resistance (17).

A poorly studied factor, probably having a lower incidence, is the influence of environmental conditions on the AH of inspired air and their effect on NIMV outcomes. A direct weak correlation was observed between ambient air RH and the humidity delivered by the ventilator (13). However, the studies were carried out in different conditions, with AH without humidification ranging from 9 to 14.7 mg·H₂O/L, thereby approaching the limit level of 15 mg·H₂O/L (12,15,16). Ambient air temperature and RH influence these parameters and differ across regions. Nevertheless, their influence is still unclear. In controlled environments, such as an intermediate respiratory care unit, variability may decrease. Other factors such as the type of ventilator, leaks and oxygen flow rate should also be considered (15).

Finally, there is no consensus on when humidification should be started during acute NIMV (5). The timing of humidification may depend on the expected length of use (5-7), as suggested by the successful early weaning protocols reducing the time of use of NIMV in patients with exacerbation of chronic pulmonary obstructive disease (26-28); clinical diagnosis, as in acute lung edema (7); or patient-reported complaints (6-8). The use of innovative humidification assessment scales could also help determine when humidification should be started (29).

Humidification may also have anecdotical but undesired effects that may affect the integrity of the skin exposed to the humidified air (30). Increased skin temperature in the area covered by the mask may cause discomfort (24).

Types of humidifiers. When should they be used?

There are two types of humidification mechanisms for use during ventilation (IMV and NIMV), which add water molecules and temperature to the air flow generated by the ventilator. Active humidifiers, also known as HHs use external heat and flow sources that can be fitted in the ventilator or used as a separated device. There are different types of HH, including bubble, counter-flow, inline and Passover vaporizers. The latter, the most widely used, heat and humidify air by passing it through a reservoir containing water previously heated at a specific temperature (6,31) (Figure 1A). They are placed in the inspiratory tube of the circuit and do not increase dead space. Although they have been associated with a higher risk of contamination and respiratory tract infections, evidence is not consistent (32). The optimal setting is using tubes with heated wires to prevent water condensation inside. Passive humidifiers are also known as HMEs. These devices recover the temperature and humidity of exhaled air to heat and humidify the air inspired from the ventilator (Figure 1B). There are different types of HME, depending on the mechanism used to recover expired air heat (hydrophobic, hygroscopic or mixed). They occasionally are fitted with a particle filter. HME vary in size and volume, which may influence outcomes.

Figure 1 Examples of humidification systems used during non-invasive mechanical ventilation. (A) Heated humidifier. (B) Heat and moisture exchanger.

For decades, the humidification mechanism of choice for IMV has been HH. The use of HME is relatively recent and has become popular for its simplicity of use, low cost, independence from a power supply and combination with a filter function (33). In intubated patients, HME has been associated with increased resistance, work of breathing and hypercapnia, mainly due to the increased dead space (33). However, significant differences have not been demonstrated between the two options in terms of airway obstruction, length of hospital stay, length of ventilation, mortality or incidence of ventilator-associated pneumonia in adult patients (34,35).

As previously noted, the use of HH is also preferred over HME in NIMV, partly due to the extensive literature available on its use in intubated patients. Only a few studies have been conducted comparing the use of the two humidification methods in patients receiving NIMV (Table 2). Most of the publications available are crossover studies using ICU double-limb ventilators and an oro-nasal mask. The studies available include a small sample of patients and compare HH with HME of different volumes. Patients had different etiologies, and considering that they were in a controlled environment, the intensity of leaks was most probably lower than in other settings. These studies were aimed at assessing physiological variables. Based on their findings, they suggest HH to be superior to HME. The main differentiating mechanism is dead space caused by HME due to its placement between the Y piece of the double-limb tube and the mask. As compared to HH, the increased dead space in HME may increase respiratory minute volume (36-40), which is related to increased respiratory rate (8,39). These data, however, are not supported by all studies (38). On the one hand, the use of HME would increase the work of inspiration (36) and work of breathing (37). Anyway, these effects can be reduced with the use of EPAP (37) or a lower-volume HME (for example, 84 vs. 36 mL) (38). Finally, increased dead space may explain the differences observed in the capacity to reduce pCO₂, especially in patients with severe hypercapnia (36,39). This finding is also controversial, as this difference was not observed in other studies using low-volume HME (37,38). These studies show that in patients with severe acidosis (pH =7.28±0.06), blood gas exchange may improve in a similar way as that achieved with HH (40). This finding might be due to potential unintentional leaks at the end of expiration, which generate a “washout effect” on the CO₂ within the mask (40). No significant differences have been reported between HH and HME regarding other blood gas exchange values, such as oxygen saturation (36-39). This hypothetical superiority of HH over HME is not supported when clinical endpoints are considered. In the largest, multicentric, international comparative study conducted to date, Lellouche et al. did not find any significant differences in terms of tolerance, length of mechanical ventilation, ICU length of stay, rate of intubation, and mortality (40). No differences were observed either in the associated sensation of dyspnea (38).

Conclusions

In summary, guidelines and expert statements generally recommend additional humidification to be delivered during NIMV. This recommendation is based on the low humidity of inspired air in the absence of a humidifier and its potential effects on the upper airways, patient comfort and tolerance. It is worth noting that some of these studies involved patients with obstructive sleep apnea and did not assess clinical endpoints that support this recommendation. Further studies are necessary to determine the need for humidification during NIMV at the acute stage of disease. Different variables should be considered in these studies, including NIMV mode (type of ventilator, type of mask...) or the specific environmental conditions of each site. The primary objective of these studies should be assessing clinical parameters that help choose the optimal timing to initiate humidification based on variables such as the expected length of use and patient characteristics and perceptions. Undesired effects and cost should also be considered. The evidence available suggests that HH is superior to HME in physiological terms, although results are inconsistent. When clinical endpoints are taken into account, the superiority of HH over HME is not that clear. Other real-life studies are needed to compare the three settings, i.e., with HH, with HME and without humidification using cutting-edge single-tube ventilators. In other settings, the clinical status of the patient, the level of pCO₂ at initiation of ventilation, the volume of the HME used, or the estimated length of use of NIMV should also be considered.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-162/rc

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-162/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-162/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. American Association for Respiratory Care. Restrepo RD, Walsh BK. Humidification during invasive and noninvasive mechanical ventilation: 2012. Respir Care 2012;57:782-8. [Crossref] [PubMed]
2. Ricard JD, Boyer A. Humidification during oxygen therapy and non-invasive ventilation: do we need some and how much? Intensive Care Med 2009;35:963-5. [Crossref] [PubMed]
3. Chaques G, Jaber S, Delay J, et al. Phoning study about postoperative practice and application of non-invasive ventilation. Ann Fr Anesth Reanim 2023;22:879-85. [Crossref] [PubMed]
4. Esquinas A, Nava S, Carrillo A, et al. Humidification and difficult endotracheal intubation in failure of noninvasive mechanical ventilation. Preliminary results. Am J Respir Crit Care Med 2008;177:A644.
5. Esquinas Rodriguez AM, Scala R, Soroksky A, et al. Clinical review: humidifiers during non-invasive ventilation--key topics and practical implications. Crit Care 2012;16:203. [Crossref] [PubMed]
6. Cerpa F, Cáceres D, Romero-Dapueto C, et al. Humification on ventilated patients: Heated humidification or heat and moisture exchangers? Open Respir Med J 2015;9:104-11. [Crossref] [PubMed]
7. Rochwerg B, Brochard L, Elliott MW, et al. Practical Application of Noninvasive Ventilation in the Hospital Setting: A supplement to the ERS/ATS Clinical Practice Guidelines for Noninvasive ventilation for Noninvasive Ventilation for Acute Respiratory Failure. Eur Respir J 2017;50:1602426. [Crossref] [PubMed]
8. Chawla R, Dixit SB, Zirpe KG, et al. ISCCM Guidelines for the Use of Non-invasive Ventilation in Acute Respiratory Failure in Adult ICUs. Indian J Crit Care Med 2020;24:S61-S81. [Crossref] [PubMed]
9. Luján M, Peñuelas Ó, Cinesi Gómez C, et al. Summary of Recommendations and Key Points of the Consensus of Spanish Scientific Societies (SEPAR, SEMICYUC, SEMES; SECIP, SENEO, SEDAR, SENP) on the Use of Non-Invasive Ventilation and High-Flow Oxygen Therapy with Nasal Cannulas in Adult, Pediatric, and Neonatal Patients With Severe Acute Respiratory Failure. Arch Bronconeumol (Engl Ed) 2021;57:415-27. [Crossref] [PubMed]
10. Gross JL, Park GR. Humidification of inspired gases during mechanical ventilation. Minerva Anestesiol 2012;78:496-502.
11. Williams R, Rankin N, Smith T, et al. Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa. Crit Care Med 1996;24:1920-9. [Crossref] [PubMed]
12. Branson RD, Gentile MA. Is humidification always necessary during noninvasive ventilation in the hospital? Respir Care 2010;55:209-16; discussion 216.
13. Holland AE, Denehy L, Buchan CA, et al. Efficacy of a heated passover humidifier during noninvasive ventilation: a bench study. Respir Care 2007;52:38-44.
14. Martins De Araújo MT, Vieira SB, Vasquez EC, et al. Heated humidification or face mask to prevent upper airway dryness during continuous positive airway pressure therapy. Chest 2000;117:142-7. [Crossref] [PubMed]
15. Lellouche F, Maggiore SM, Lyazidi A, et al. Water content of delivered gases during non-invasive ventilation in healthy subjects. Intensive Care Med 2009;35:987-95. [Crossref] [PubMed]
16. Oto J, Nakataki E, Okuda N, et al. Hygrometric properties of inspired gas and oral dryness in patients with acute respiratory failure during noninvasive ventilation. Respir Care 2014;59:39-45. [Crossref] [PubMed]
17. Richards GN, Cistulli PA, Ungar RG, et al. Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance. Am J Respir Crit Care Med 1996;154:182-6. [Crossref] [PubMed]
18. Fontanari P, Burnet H, Zattara-Hartmann MC, et al. Changes in airway resistance induced by nasal inhalation of cold dry, dry, or moist air in normal individuals. J Appl Physiol (1985) 1996;81:1739-43. [Crossref] [PubMed]
19. Rakotonanahary D, Pelletier-Fleury N, Gagnadoux F, et al. Predictive factors for the need for additional humidification during nasal continuous positive airway pressure therapy. Chest 2001;119:460-5. [Crossref] [PubMed]
20. Wiest GH, Lehnert G, Brûck WM, et al. A heated humidifier reduces upper airway dryness during continuous positive airway pressure therapy. Respir Med 1999;93:21-6. [Crossref] [PubMed]
21. Massie CA, Hart RW, Peralez K, et al. Effects of humidification on nasal symptoms and compliance in sleep apnea patients using continuous positive airway pressure. Chest 1999;116:403-8. [Crossref] [PubMed]
22. Esquinas A, Escobar C, Chávez A, et al. Noninvasive mechanical ventilation and humidification in acute respiratory failure. a morpho histological and clinical study of side effects. Am J Respir Crit Care Med 2002;165:A835.
23. Hayes MJ, McGregor FB, Roberts DN, et al. Mouth leaks with nasal positive airway pressure increases nasal airway resistance. Thorax 1995;50:1179-82. [Crossref] [PubMed]
24. Hart D, O’Dochartaigh S, Beaumont-Orr J, et al. The effects of heated humidification in patients on non-invasive ventilation (NIV) for acute respiratory failure. Eur Respir J 2013;42:2483.
25. Hess DR. Noninvasive ventilation for acute respiratory failure. Respir Care 2013;58:950-72. [Crossref] [PubMed]
26. Damas C, Andrade C, Araújo JP, et al. Weaning from non-invasive positive pressure ventilation: experience with progressive periods of withdraw. Rev Port Pneumol 2008;14:49-53.
27. Lun CT, Chan VL, Leung WS, et al. A pilot randomised study comparing two methods of non-invasive ventilation withdrawal after acute respiratory failure in chronic obstructive pulmonary disease. Respirology 2013;18:814-9. [Crossref] [PubMed]
28. Sellares J, Ferrer M, Anton A, et al. Discontinuing noninvasive ventilation in severe chronic obstructive pulmonary disease exacerbations: a randomised controlled trial. Eur Respir J 2017;50:1601448. [Crossref] [PubMed]
29. Pan L, Hong Y, Zhong X, et al. A Novel Scale to Assess Humidification during Noninvasive Ventilation: A Prospective Observational Study. Can Respir J 2023;2023:9958707. [Crossref] [PubMed]
30. Alqahtani JS, Worsley P, Voegeli D. Effect of Humidified Noninvasive Ventilation on the Development of Facial Skin Breakdown. Respir Care 2018;63:1102-10. [Crossref] [PubMed]
31. Al Ashry AS, Modrykamien AM. Humification during mechanical ventilation in the adult patient. Biomed Res Int 2014;2014:715434. [Crossref] [PubMed]
32. Picazo L, Gracia Arnillas MP, Muñoz-Bermúdez R, et al. Active humidification in mechanical ventilation is not associated to an increase in respiratory infectious complications in a quasi-experimental pre-post intervention study. Med Intensiva (Engl Ed) 2021;45:354-61. [Crossref] [PubMed]
33. Lucato JJJ, Cunha TMND, Reis AMD, et al. Ventilatory changes during the use of heat and moisture exchangers in patients submitted to mechanical ventilation with support pressure and adjustments in ventilation parameters to compensate for these possible changes: a self-controlled intervention study in humans. Rev Bras Ter Intensiva 2017;29:163-70. [Crossref] [PubMed]
34. Gillies D, Todd DA, Foster JP, et al. Heat and moisture exchangers versus heated humidifiers for mechanically ventilated adults and children. Cochrane Database Syst Rev 2017;9:CD004711. [Crossref] [PubMed]
35. Siempos II, Vardakas KZ, Kopterides P, et al. Impact of passive humidification on clinical outcomes of mechanically ventilated patients: a meta-analysis of randomized controlled trials. Crit Care Med 2007;35:2843-51. [Crossref] [PubMed]
36. Jaber S, Chanques G, Matecki S, et al. Comparison of the effects of heat and moisture exchangers and heated humidifiers on ventilation and gas exchange during non-invasive ventilation. Intensive Care Med 2002;28:1590-4. [Crossref] [PubMed]
37. Lellouche F, Maggiore SM, Deye N, et al. Effect of the humidification device on the work of breathing during noninvasive ventilation. Intensive Care Med 2002;28:1582-9. [Crossref] [PubMed]
38. Boyer A, Vargas F, Hilbert G, et al. Small dead space heat and moisture exchangers do not impede gas exchange during noninvasive ventilation: a comparison with a heated humidifier. Intensive Care Med 2010;36:1348-54. [Crossref] [PubMed]
39. Lellouche F, Pignataro C, Maggiore SM, et al. Short-term effects of humidification devices on respiratory pattern and arterial blood gases during noninvasive ventilation. Respir Care 2012;57:1879-86. [Crossref] [PubMed]
40. Lellouche F, L’Her E, Abroug F, et al. Impact of the humidification device on intubation rate during noninvasive ventilation with ICU ventilators: results of a multicenter randomized controlled trial. Intensive Care Med 2014;40:211-9. [Crossref] [PubMed]