key: cord-0037602-asy597em
authors: Esquinas, Antonio Matías; Al-Jawder, Suhaila E.; BaHammam, Ahmed S.
title: Practice of Humidification During Noninvasive Mechanical Ventilation (NIV): Determinants of Humidification Strategies
date: 2011-05-25
journal: Humidification in the Intensive Care Unit
DOI: 10.1007/978-3-642-02974-5_11
sha: d7a1cce76ed4313649eba256bf7bad67686850d1
doc_id: 37602
cord_uid: asy597em

1. Who will benefit from humidification? 2. When to apply humidification? 3. How to incorporate humidification into NIV?

The provision of heat and humidity during mechanical ventilation (MV) is a standard of care worldwide [ 1 ] . There is an international consensus on the importance of humidifi cation during invasive mechanical ventilation. The two humidifi cation methods used during invasive MV are: the heated humidifi er and the heat-and-moisture exchange (HME). Noninvasive mechanical ventilation (NIV) is increasingly used in intensive care units (ICU) and emergency departments. Currently, it is the standard of care in the treatment of acute exacerbation of chronic obstructive pulmonary disease (COPD), acute cardiogenic pulmonary edema (CPE), and immunocompromised patients [ 2, 3 ] . Furthermore, NIV is available for home use for patients with sleep-related breathing disorders and chronic respiratory failure.

The routine use of humidifi cation during NIV is controversial. There is no consensus statement defi ning the indications, patient selection, device selection, etc. The literature provides some evidence in terms of improving patient comfort and some other physiological parameters. However, well-designed studies are necessary to provide clear evidence to support or discourage the use of humidifi cation in NIV [ 4, 5 ] .

This chapter focuses on the use of humidifi cation in NIV especially when applied to patients with acute respiratory failure (ARF). The physiological aspects of humidifi cation have been covered thoroughly in other chapters of this book. The available data in the literature will be reviewed in order to develop an adequate strategy for the use of humidifi cation in NIV.

The available data in this fi eld are very scant. In addition, the published studies have a number of limitations that make their interpretation and the development of a clear approach for humidifi cation diffi cult.

The following challenges are facing the development of a standard approach to humidifi cation in NIV: 1. Absence of a consensus statement in this regard despite the availability of statements and recommendations that guide the overall use of NIV [ 2, 4 ] . 2. Clinical and bench studies do not always refl ect the actual practice because of the interaction of many variables in real patients [6] [7] [8] .

3. No comprehensive survey has been conducted among practitioners [ 5 ] . 4. Finally, the development of proper clinical practice guidelines depends to a large extent on the availability of randomized clinical trials in well-defi ned populations [ 9, 10 ] . Such data are missing at this stage. Initial reports that alerted practitioners to the importance of humidifi cation in patients on NIV came from observational studies conducted on patients with ARF. Those reports drew the attention of practitioners to the benefi cial effects of applying humidifi cation in NIV and the potential complications of inhaling dry gas [11] [12] [13] .

The international consensus document on NIV published in 2001 did not thoroughly address the use of humidifi cation in NIV because of insuffi cient data at that time, especially in applying NIV to patients with ARF [ 2 ] . In the last decade, there has been a major technological breakthrough in the manufacturing of humidifi ers and a better understanding of how to incorporate these new humidifi ers into the conventional devices of NIV. For example, with some of these humidifi ers, some potential benefi cial effects were described on the control of hypercapnia and work of breathing (WOB) [ 13 ] . Furthermore, a form of agreement that humidifi cation of inspired gases should be a standard of care has begun to evolve among specialists [ 1 ] . Since 2005, a growing number of studies on the use of humidifi cation in NIV have been published. In this chapter, we discuss the international survey we conducted in 2008 in 15 hospitals to explore the practice of incorporating humidifi cation in NIV [ 5 ] . This chapter focuses on three key questions: 5. Who will benefi t from humidifi cation? 6. When to apply humidifi cation? 7. How to incorporate humidifi cation into NIV?

NIV has been accepted worldwide as a standard of care for a number of respiratory disorders with clear indications in the emergency or home settings [ 1 ] . However, the practice of using humidifi cation with NIV is not practiced routinely. Today, we understand that NIV may adversely infl uence the normal humidifi cation system in the body and hence decrease moisture of the inspired gas [ 4 ] .

Evaluating the response of the upper and lower airways in asthmatic patients hyperventilating cold air and breathing through the mouth demonstrated a decrease in FEV1 and an increase in nasal resistance [ 4 ] . Additionally, controlled asthmatics who are mouth breathers are also found to have an increase in nasal airway resistance [ 14 ] . Perhaps in obstructive crisis, when patients breathe through the mouth, insuffi cient moisture can play an important role, though this has yet to be documented.

One of the objectives of early use of humidifi cation during noninvasive ventilation is to enhance tolerance and subsequent compliance with NIV. Discomfort or intolerance of NIV devices can result from different factors. Dryness of the mucous membranes is one of the major contributing factors. Clinical trials are needed to determine whether the application of humidifi cation can improve tolerance and enhance compliance to NIV [ 11, 14 ] .

Humidifi cation requirements should be tailored to the clinical characteristics and needs of each patient. Therefore, it is necessary to consider conditions that infl uence the moisture of the airway such as diseases of the respiratory mucosa, nasal septum deviation, medications, ventilator setting, and types of interfaces [ 14 ] . Nasal masks promote mouth leaks and therefore high unidirectional nasal fl ow, which results in increased nasal resistance and mouth opening, which in turn perpetuate mouth leak [ 14, 15 ] . Heated humidifi cation as discussed in other chapters of this book acts by increasing the relative humidity (RH) of the air, reducing nasal resistance, and possibly increasing adherence to NIV.

The available literature lacks large-scale studies that evaluate the use of humidifi cation for early and acute application of NIV. In clinical practice, it has been observed that some complications have developed in the absence of humidifi cation and have contributed directly or indirectly to NIV failure and diffi culties in endotracheal intubation [ 16 ] . The literature also lacks information about the frequency of this problem in patients with ARF on NIV. However, the application of a heated humidifi er has proven to be useful and safe in the control of associated symptoms such as mucosal dryness, and therefore may contribute to improved comfort and compliance, especially in patients with chronic stable respiratory diseases [ 17, 18 ] . The development of an algorithm that stratifi es patients into different risk groups is essential. Knowledge of the above-mentioned information and training and experience of the medical team applying the NIV are necessary to create a successful algorithm that can provide proper NIV application strategies.

Some factors that can infl uence the decision for early use of humidifi cation are: 1. Cost-effectiveness :

The economic aspect and the cost of implementing humidifi cation strategies is another considerable factor that can infl uence the selection of the humidifi er to treat patients on NIV. A status of balance between the cost and the benefi ts of humidifi cation should be achieved particularly when considering short-term use of NIV [ 18 ] . With regard to invasive mechanical ventilation (IMV), clinical aspects such as the duration of IMV, the increased risk of developing ventilatorassociated pneumonia and weaning diffi culties are well identifi ed and important outcomes that favor the routine and early use of humidifi cation [ 19, 20 ] . Unfortunately, in the case of NIV such clinical outcomes are not well identifi ed and studied. Nevertheless, the development of complications as a result of not using proper humidifi cation in patients with ARF treated with NIV will add to the cost of ARF treatment. Furthermore, failure of NIV for any reason will lead to a more costly intervention, such as endotracheal intubation. Therefore, it would be reasonable to identify patients on NIV at a moderate to high risk of developing complications if not using humidifi cation and provide them with early humidifi cation. One of the serious complications is the diffi culty experienced with endotracheal intubation, which is attributed to the dryness of the upper airway mucosa [ 5, 8, 16, 21 ] .

The use of an early humidifi cation strategy is required in respiratory failure secondary to some respiratory diseases, such as COPD and asthma, where the introduction of humidifi cation has shown favorable effects [ 12, 14 ] .

When discussing the available data pertaining to humidifi cation in NIV, we have to categorize ARF into hypoxemic and hypercapnic. In patients with hypoxemic ARF, data supporting the use of humidifi cation are available for those requiring FiO 2 greater than 0.60 and those who are expected to require a prolonged use of NIV (>2 h) [ 15, 16 ] .

In patients with hypoxemic ARF, data supporting the use of humidifi cation are available for those requiring FiO 2 greater than 0.60 and those who are expected to require a prolonged use of NIV (>2 h) [ 22 ] and characteristics of bronchial secretions [ 12, 23 ] .

The use of ventilatory parameters infl uences moisture loss. The higher the tidal volume ( V T ) and the higher the peak inspiratory fl ow rate, as with the NIV-CPAP systems, the greater the moisture loss is. Therefore, these physical conditions should be considered when applying NIV. Early institution of humidifi cation reduces the effects of V T and fl ow rate on humidity [ 12, 24 ] .

The rheological property of the viscosity of bronchial secretions is an important determinant of the early humidifi cation strategy, especially in critically ill patients, as discussed in other chapters of this book [ 25 ] . The loss of these characteristics leads to retention of the bronchial secretions, especially in the distal airways of the bronchial system that are diffi cult to draw from, and results in increased airway resistance, impaired gas exchange, and airway obstruction, etc. [ 6, 15, 21 ] . The early combination of proper humidifi cation with cough-assist techniques is useful and can improve the outcome of the NIV. Other factors that can encourage an early implementation of humdifi cation include: older age, increased nasal resistance, mucociliary dysfunction, medication that can cause dehydration of the mucosa, chronic nasal or respiratory diseases, mouth breathing, and bronchial hypersecretion, especially if associated with COPD or bronchiectasis [ 21, 23, 25 ] . Despite the long list of proposed benefi ts of humdifi cation in NIV, it is usually used without humdifi cation, and controversy still exits regarding humidifi cation effi cacy [ 1, 4 ] . More studies are needed to document the benefi ts of humidifi cation in patients with ARF who require NIV. Although we still need more evidence, the application of humidifi cation in the above-discussed conditions is encouraged. Contrarily, some factors deter the routine use of humidifi cation in NIV. These factors include: 1. Absence of a consensus on the criteria needed to identify the appropriate candidates and indications for early humidifi cation use. 2. In some cases, the humidifi er model used can induce asynchronization problems via different mechanisms [ 6, 13, 19, 26, 27 ] : I. Increasing the largest dead space, II. Increasing work of breathing, III. Rebreathing problems, IV. Causing a drop in inspiratory positive pressure. 3. Humidifi er use may increase the cost of treatment with NIV [ 18 ] . 4. Concerns with cross-infection may limit the use of humidifi ers. Heat-moisture exchange (HME) use for short-term NIV in patients with ARF is associated with less cross-infection [ 28 ] . The heated humidifi er may carry a greater risk of spreading aerosols of respiratory viral infections (SARS, H1N1) or Mycobacterium tuberculosis . Nevertheless, the currently published work of the International Network Group, which was analyzed during the H1N1 pandemic, did not demonstrate such an association [ 29 ] . However, with the long-term use of NIV at home for OSAS, a potential risk of colonization and infection was described [ 30 ] .

1. Hospital organization .

In some institutions, the decision to use humidifi cation in NIV depends on the setting where the NIV is applied, such as emergency departments, intensive care units, or outpatient settings. Humidifi cation is recommended when high-fl ow NIV-CPAP is used in patients at high risk even if it is going to be used for a short time [ 24 ] . Such practice is mostly seen in critically ill patients in the medical ICU or postoperative recovery units [ 31 ] . 2. Geographical data .

The differences in humidity among countries would suggest a variation in the practice of humidifi cation use. Nevertheless, the International Survey in Humidifi cation Practice did not suggest these geographical factors to be important in the practice of humidifi cation [ 5 ] . The European Survey of Noninvasive Ventilation Practices showed that humidifi cation practice is common in Europe [ 3 ] .

Surprisingly, no epidemiological survey has been conducted analyzing the practice of NIV humidifi cation and its effects on short-term outcomes that can guide humidifi cation practice [ 3, 5, 31 ] . Below is a summary of the available data.

There are no data to support one humidifi cation system over the other or to demonstrate the superiority of one over the other in terms of hygrometry effi cacy or absolute humidity. The selection of the humidifi cation system depends on other factors such as the interface (nasal, facial, helmet) [ 32 ] , and the type of mechanical ventilator (home mechanical ventilator, high fl ow CPAP systems or ICU mechanical ventilators) [ 3, 5, 24, 31 ] . i. Heated humidifi er (HH) The HH acts as an active system to increase the AH to acceptable levels with a minimal effect on the set inspiratory positive airway pressure (IPAP) (on average IPAP can decrease by a value of 0.5-1 cmH 2 O) [ 20 ] . Currently HHs are preferred when the air is dry and cold with retention of bronchial secretions [ 26 ] . Unidirectional fl ow causes nasal mucosal dryness, promotes the release of infl ammatory mediators, and increases nasal resistance [ 15, 21 ] . The HH increases the RH in the air, reduces nasal airway resistance, and may increase adherence to the NIV compared to HMEs [ 6, 8, 9, 17, 26, 33 ] .

ii. Heat and moisture exchanger (HME) As defi ned in other chapters, the HME acts by conserving moisture endogenously in the breathing circuit and is used when the patient has suffi cient capacity to maintain AH of the inspired air. It is recommended to be applied early, but not recommended with all types of interfaces (nasal mask or face mask). They are ideal for the helmet system. Chanques et al. found that the humidifi ers most commonly used are HMEs (52%), followed by HHs (26%), both (4%), and neither (19%) in postoperative resuscitation units. In our international survey, we analyzed the information from 15 hospitals including information on 1635 patients who had been treated with NIV in 2008 [ 5 ] (Fig. 11.1 ). When the results were analyzed in relation to the humidifi cation system used, we found that the heated wire humidifi er (HWH) was used most frequently (46.6%). No differences between countries, types of hospital settings, or acute care units were observed. This is different from the results of Chanques et al., who analyzed data collected from post-surgical observation units [ 31 ] .

Humidifi er availability is infl uenced by several factors, including hospital area (acute care units, general wards, or out-patient setting), the type of ARF, the type of ventilator and interface used, and the number of patients treated simultaneously with NIV. The above are factors that determine the availability and type of humidifi er to be selected [ 3, 5 ] . 3. Protocols of humidifi cation .

In our survey, we observed that 40% of the surveyed hospitals do not have written protocols to guide the use of humidifi cation in NIV. The utilization of Education is of paramount importance to achieve proper implementation and optimal results of humidifi cation in NIV [ 26 ] . Our survey revealed that there was no formal training or education for NIV and humidifi cation in the surveyed hospitals.

There are no large epidemiological studies to determine the best strategy for humidifi cation in NIV. However, based on the available data, the best strategy to ensure proper application of humidifi cation in NIV is to fi rst indentify the factors that may affect humidifi cation and enhance moisture loss in patients with ARF, and then to apply the proper humidifi cation system that suits each case based on the patient's 11 .3 Protocols of humidifi cation practice and type of humidifi ers used. HWH heated wire humidifi er, HME heat and moisture exchanger. Models HWH used: hwh -fp-mru830-1; hwh-fp-(*mr730, and others models = 1); hwp-fp= (410s, 810s) = 1. FP = fi sher@paykel models clinical condition, the ventilator parameters, and the interface used. Early application of humidifi cation may benefi t patients with hypoxemic respiratory failure or obstructive pulmonary diseases, and patients on high-fl ow CPAP systems, or who need prolonged use of NIV. Multi-center studies with large numbers of patients are needed to identify the patient groups who are likely to benefi t from the addition of humdifi cation to NIV therapy and to assess the effect of humidifi cation on adherence to NIV, and its effect on different outcome measures.

Humidifi cation of respired gases during mechanical ventilation: mechanical considerations

International Consensus Conferences in Intensive Care Medicine: non-invasive positive pressure ventilation in acute respiratory failure. Organised jointly by the

A European survey of noninvasive ventilation practices

Is humidifi cation always necessary during noninvasive ventilation in the hospital?

Humidifi cation and diffi cult endotracheal intubation in failure of noninvasive mechanical ventilation (NIV). Preliminary results

Comparison of the effects of heat and moisture exchangers and heated humidifi ers on venti lation and gas exchange during non-invasive ventilation

Water content of delivered gases during non-invasive ventilation in healthy subjects

Heated humidifi cation or face mask to prevent upper airway dryness during continuous positive airway pressure therapy

Quality of life, compliance, sleep and nasopharyngeal side effects during CPAP therapy with and without controlled heated humidifi cation

Routine use of humidifi cation with nasal continuous positive airway pressure

Causes of failure of noninvasive mechanical ventilation

Inspissated secretions: a life-threatening complication of prolonged noninvasive ventilation

Effect of the humidifi cation device on the work of breathing during noninvasive ventilation

Interfaces and humidifi cation for noninvasive mechanical ventilation

Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance

Absolute humidity variations with a variable inspiratory oxygenation fraction in noninvasive mechanical ventilation (NIV). A pilot study

Effect of heated humidifi cation on compliance and quality of life in patients with sleep apnea using nasal continuous positive airway pressure

Comparison of two humidifi cation systems for long-term noninvasive mechanical ventilation

Impact of passive humidifi cation on clinical outcomes of mechanically ventilated patients: a meta-analysis of randomized controlled trials

Mechanical effects of airway humidifi cation devices in diffi cult to wean patients

Effects of gas leak on triggering function, humidifi cation, and inspiratory oxygen fraction during noninvasive positive airway pressure ventilation

Airways humidifi cation during mechanical ventilation. Effects on tracheobronchial ciliated cells morphology

Effects of a heat and moisture exchanger and a heated humidifi er on respiratory mucus in patients undergoing mechanical ventilation

Humidifi cation of rapidly fl owing gas

Mucociliary clearance is impaired in acutely ill patients

Effi cacy of a heated passover humidifi er during noninvasive ventilation: a bench study

Small dead space heat and moisture exchangers do not impede gas exchange during noninvasive ventilation: a comparison with a heated humidifi er. Intensive Care Med [Comparative Study Randomized Controlled Trial Research Support

On the role of non-invasive (NIV) to treat patients during the H1N1 infl uenza pandemic

Humidifi cation practice during H1N1 pandemic. International Survey (unpublished data)

Effect of continuous positive airway pressure therapy on infectious complications in patients with obstructive sleep apnea syndrome

Phoning study about postoperative practice and application of non-invasive ventilation

Effect of a heated humidifi er during continuous positive airway pressure delivered by a helmet

Use of heated humidifi cation during nasal CPAP titration in obstructive sleep apnoea syndrome