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The Open Respiratory Medicine Journal, 2015, 9, (Suppl 2: M5) 104-111
104
Open Access
Humidification on Ventilated Patients: Heated
Humidifications or Heat and Moisture Exchangers?
F. Cerpa1, D. Cáceres1, C. Romero-Dapueto1, C. Giugliano-Jaramillo1,
*,1
R. Pérez1, H. Budini1, V. Hidalgo1, T. Gutiérrez1, J. Molina2 and J. Keymer
1
Servicio de Medicina Física y Rehabilitación, Clínica Alemana de Santiago, Santiago, Chile
2
Escuela de Kinesiología, Universidad del Desarrollo, Santiago, Chile
Abstract: The normal physiology of conditioning of inspired gases is altered when the patient requires an artificial airway
access and an invasive mechanical ventilation (IMV). The endotracheal tube (ETT) removes the natural mechanisms of
filtration, humidification and warming of inspired air. Despite the noninvasive ventilation (NIMV) in the upper airways,
humidification of inspired gas may not be optimal mainly due to the high flow that is being created by the leakage
compensation, among other aspects. Any moisture and heating deficit is compensated by the large airways of the
tracheobronchial tree, these are poorly suited for this task, which alters mucociliary function, quality of secretions, and
homeostasis gas exchange system. To avoid the occurrence of these events, external devices that provide humidification,
heating and filtration have been developed, with different degrees of evidence that support their use.
Keywords: Air humidification, Humidification devices, humidification IMV, humidification NIMV.
1. INTRODUCTION
2. PHYSIOLOGICAL CONCEPTS
The human airway has an important role in heating and
humidification of the inspired gas [1]. During spontaneous
breathing, inspiratory gases are usually heated and
humidified in the nasal cavity and pharynx [2]. The normal
physiology of conditioning gas is altered when the patient
requires an artificial airway, intubation eliminates the natural
mechanisms of filtration, humidification, and warming of
inspired air [3]. The humidification of inspired gas is
mandatory for all mechanically ventilated patients, however,
the debate about the ideal humidification continues today
[4].
2.1. Humidification
NIMV supplies dry and cold gas through the upper
airway causing dryness of the mucosa and respiratory
dysfunction. Leakage compensation applied by NIMV
creates high flow throughout the respiratory cycle, which
contributes to the loss of heat and humidity [5]. Although in
NIMV the upper airway is preserved, humidification during
NIMV might not be optimal due to the greater flow
delivered, thus producing an increase in mucous viscosity
and secretion retention, these conditions that increase the
risk of obstruction of the upper airways [6].
During NIMV, active humidification is recommended to
improve patient comfort [7]. But in which patients, it
provides better evidence and Is it always necessary in
hospitalized patients?
*Address correspondence to this author at the Servicio de Medicina Física y
Rehabilitación, Clínica Alemana de Santiago, Avenida Vitacura 5951,
Vitacura, Santiago, Chile; Tel: +56222101421; Fax: +56222101421;
E-mail: jkeymer@alemana.cl
1874-3064/15
Humidity refers to the quantity of water vapor in a
gaseous environment [4] and it depends on the temperature
of the gas and it can be expressed in two ways, as absolute
humidity and relative humidity. The absolute humidity (AH)
is the amount of water in a given volume of gas usually
expressed in H2O mg/L volume [4, 8]. The relative humidity
(RH) is the amount of water vapor in a volume of gas,
expressed as a percentage of the amount of water vapor
required to fully saturate the same volume of gas at the same
temperature and pressure [4].
If atmospheric air is at 20°C, and has an AH H2O of
about 10 mg/L water and RH of 55 to 60%. As this air passes
through the nose and upper respiratory tract, it humidifies
and heats the air [4]. This occurs thanks to the fact that in
nasopharynx the inspired gases are exposed to a highly
vascularized moist mucous membrane [9]. The respiratory
mucosa is lined by ciliated columnar pseudostratified
epithelium and numerous goblet cells, these cells and
submucosal glands are responsible for maintaining the
mucosal layer that serves as a trap for the pathogens and as
an interface for the exchange of moisture. At the level of the
terminal bronchioles, the epithelium becomes a simple cubic
type with minimum goblet cells and few submucosal glands.
Therefore, the capacity of these pathways to perform the
same level of humidification than the upper airway is limited
[8, 10].
The movement of the cilia is called metachronalciliary;
the beat frequency is directly proportional to the temperature
(t°) and it is normal that at 37°C it is 750 b/min, but at 40°C
it increases to 1100 b/min. Excessive moisture affects ciliary
2015 Bentham Open
Humidification on Ventilated Patients
The Open Respiratory Medicine Journal, 2015, Volume 9
function, since it increases the volume of secretions due to
its low viscosity and risk of atelectasis by plugging the
airway [11]. This explains why at a temperature above 37°C
and 100% gas saturation produces a condensation of the gas,
thus causing a reduction in mucus viscosity and an increase
in the thickness of the pericellular liquid, which may be too
liquid to be coupled properly to the tips of the cilia, thus
affecting mucociliary transport [12, 13].
As the air moves forward through the respiratory tract, it
will be thermo-humidified, at the middle of the trachea the
temperature and the AH reaches approximately 34°C and 34
to 38 mg H2O/L respectively [14]. The point at which the
gas reaches 37°C and a relative humidity of 100% (which
corresponds to an absolute humidity of 44mgH2O/L), it is
known as the limit of isothermal saturation, which is about 5
cm below the carina during quiet breathing between the third
and the fifth generation of the bronchial tree [14, 15]. This
provides optimal conditions for gas exchange in the alveolarcapillary membrane [4]. Humidity and temperature are
constant below the limit of isothermal saturation [14].
The upper airway delivers 75% of the heat and humidity
delivered to the alveoli. If the physiological conditions
change, either by having an ETT during the IMV or when
changing the flow and pressure conditions during NIMV,
there is not an adequate system of humidification for our
patients. The point of isothermal saturation could be
affected, any moisture and heating deficit is compensated by
the large airways of the tracheobronchial tree, which are
unsuitable for this task, thus altering the mucociliary
function, quality of secretions, and the homeostasis system
gas exchange.
2.2. Humidification Devices
Humidifiers are devices that add water molecules, gas
and temperature. They are classified as active if they have
external sources of heat, water and flow, and passive if they
use temperature and hydration from the exhaled gas from
patients [16]. See Table 1.
Table 1.
2.3. Active Humidifiers
These types of humidifiers are divided into several
categories: bubble humidifiers, waterfall humidifiers, bypass
humidifiers and shirt humidifiers [8]. Of the active
humidification systems, the bypass is the most widely used
today in the ICU, they are applied in both, in mechanical
ventilation and noninvasive ventilation [7]. The gas that goes
to the patient passes over the surface of the heated water,
which causes the humidification to come close to 100% RH
and can deliver up to 44 mg/L of AH [17, 18].
The water is heated via heating base, which transmit heat
by convection from the metal of the bases. It is selfregulating by a servomechanism and consist of: a heating
cable, (which maintains the temperature of gas in the circuit,
thus preventing condensation in the piping and the
probability of bacterial colonization), a cable with two
temperature sensors, which are locked at the output of the
humidifier, and a Y-piece (near the patient) to servo-control
the temperature of the system [18, 19]. In most modern
devices, the temperature is preset at 37°C [20]. This system
maintains control of the gas temperature to the patient,
regardless of changes in the gas flow or water level in the
reservoir, despite having a slow time of reaction [21]. The
water that condenses the pipes is considered contaminated,
and should not be returned to the humidifier [19]. The main
problem with this device is that it does not filter particles
[22].
2.4. Passive Humidifiers
Are disposable heat and moisture exchangers (HME),
some with a particle filter. They are lightweight, inexpensive
and easy to use with standard connectors for IMV [23]. They
contain a high contact surface of paper, with compressed
metallic elements which capture particles of exhaled water
vapor and heat, holding and releasing it in the next
inspiration. To fulfill this function, the HME can be
Hydrophobic (HMEF, Heat-and-Moisture Exchanger Filter)
Hygroscopic (HHME, Hygroscopy Heat-and-Moisture
Exchanger) or both with filter (HHMEF, Hygroscopy Heatand-Moisture Exchanger and filter). This data are shown in
Advantages and disadvantages of HH and HME.
Devices
Advantages
Disadvantages
Universal application
Cost
Reliability
Using water
Alarms
Condensation
Wide ranges of temperature and humidity
Risk of contamination
Temperature monitoring
Low possibility of electrical shock and burns
Reaches the maximum absolute humidity
no Filter
Cost
Does not apply to all patients
Passive operation
Increased dead space
Active
Passive
105
User friendly
Increased resistance
Removal of condensation
Potential occlusion
Portable
Misting problems
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The Open Respiratory Medicine Journal, 2015, Volume 9
Table 2.
Cerpa et al.
Types of heat-and-moisture exchanger.
Function
Absolute Humidity
HME
Hydrophobic
10-14 mgH2O/L
HMEF (Heat-and-Moisture Exchanger Filter):
Hydrophobic + Filter
18-28 mgH2O/L
HHME (Hygroscopy Heat-and-Moisture Exchanger):
Hydrophobic + Hygroscopic
22-34 mgH2O/L
HHMEF (Hygroscopy Heat-and-Moisture Exchanger):
Hydrophobic + Hygroscopic + Filter
23-35 mgH2O/L
Table 2. Hygroscopic is an adjective of a compound
chemical material, which absorbs moisture from the air. The
aluminum material of this device quickly exchanges
temperatures when expiration condensation is formed
between the layers of this material. The retained heat and
moisture are returned during inspiration. Adding a fibrous
element helps retain moisture and reduces the accumulation
of condensation in the dependent position of the device [24,
25]. Hydrophobic is an adjective for those substances or
elements that repel water and cannot mix or absorb. They use
a paper or polypropylene treated with calcium or lithium
chloride, to increase moisture conservation and repel water
that is not absorbed [26]. It is Important to mention that these
devices also function as a bacterial filter [17]. The HME are
installed between the Y-piece of the patient, which can
increase the resistance to airflow, not only during inspiration,
but also during expiration. The minimum resistance to the
flow is 0.5 to 3.6 cm H2O/L/sec [27, 28]. It is important to
take into account the dead space produced by these devices,
which can be variable. Among different devices according to
some measurements, it can reach 95 mL [29, 30]. Passive
humidifiers should never be used in conjunction with active
humidifiers [31].
If water or fluids occlude the HME, the patient is not
ventilated properly, and may be unable to fully exhale during
ventilation with positive pressure [32]. Studies recommend
using HHMEF for their hydrophobic, hygroscopies and filter
characteristics, as shown in Table 2 [9].
3. WHAT IS THE MINIMUM VALUE OF MOISTURE
THAT A DEVICE MUST DELIVER?
The American National Standards Institute (ANSI) and
the American Association for Respiratory Care (AARC)
recommend an AH ≥30 mg H2O/L for the inspired air during
mechanical ventilation [16, 33], while the ISO (International
Organization for Standardization) prefer AH values ≥ 33 mg
H2O/L [34]. It is important to consider that the performance
specifications provided by the manufacturers of HMEs are
based on in vitro measurements when delivering moisture,
using the ISO 9360 method [7, 35]. However the in vivo
performance of HMES may differ from the manufacturer's
specifications when defining the ability to heat and
humidify, these configurations do not fully reflect the
physiology of human respiration [7, 36]. An important aspect
is that we have to know the performance of the devices we
use in our unit. In a study by Lellouche et al. in 2009 [29]
tested 32 HME and showed that only 37.5% had a good
performance (> or = 30 mg H2O/L), while 25% did poorly
(<25 mg H2O/L). The difference in values between their
measurements and the data supplied by the manufacturer
regarding the humidification was 3.0 ± 2.7 mg H2O/L, that is
why we must check if the devices at our units have been
tested and if they meet the standard, regardless of what the
manufacturer states. Restrepo et al. [7] states that the device
to use, either active or passive, must provide a moisture level
of 33 mg H2O/L and 44 mg H2O/L and a temperature
between 34°C and 41°C with a RH 100% to prevent drying
of secretions in the artificial airway.
4. HUMIDIFICATION IN IMV, WHICH DEVICE CAN
WE USE?
The Mechanical ventilation delivered through a tracheal
tube (ETT) to critically ill patients, requires appropriate
heating, moistening and filtering of the airway in order to
counteract bypassing of the upper respiratory tract due to the
use of an ETT [37]. Any moisture deficit must be offset by
the large airways of the tracheobronchial tree, which are
poorly suited for this task, the gas with low RH rapidly
absorbs moisture from the tracheobronchial mucosa and
secretions in the airway, this can result in dry secretions,
plugging with mucus, and obstruction of the airways [38].
The heating and humidifying of inspiratory gas, with
different devices, can prevent complications associated with
dryness of the respiratory mucosa, which can lead to the
occlusion of the ETT [39]. That is why the humidification is
recommended in all patients receiving IMV with a level of
evidence 1A [7].
There are variables that could affect us in the moistening,
and can influence the choice of the appropriate humidifying
device:
4.1. Ambient Air Temperature
Lellouche et al. [40] measured two passive and one
active/passive (Hudson Heat Teleflex Humid-Medical)
HMEs, at three different environment temperature (22 to
30°C), and concluded that there is a negligible effect of room
temperature in the moisture delivered by HMEs, since these
devices can be used to provide adequate moistening in
different climates.
4.2. Minute Ventilation (VE)
Various studies that measure the impact of tidal volume
(VT), respiratory rate (RR) and minute ventilation (VE) in
humidification, have used high VT from 0.5 to 1.0 L and
higher VE between 10 and 20 L/min [41]. A randomized
controlled trial that compared HME with hydrophobic
properties, an HME with hydrophobic and hygroscopic
properties compared and HH, with minute ventilation of 10.8
Humidification on Ventilated Patients
L/min, 11.6 L/min and 10.2 L/min, showed that after 72
hours, the internal diameter of the ETT had decreased 6.5
mm with hydrophobic HME, 2.5mm with hygroscopic and
hydrophobic HME, and 1.5 mm with an HH [42]. This
would allow the conclusion that in patients with high VE
(over 10 L/min), we should choose a HH. In a recent study
Lellouche et al. [40] they reached the conclusion that VE
variation was not significant in the HME humidification
performance when using VT of 0.5 and 0.65 L, with a
respiratory rate of 20 to 30 breaths/minute, and with VE of
10 and 20 L/M, respectively. An important aspect to
consider is that the strategies mentioned above do not
correlate with lung protective strategies for IMV. The current
guidance of ventilation strategies is based on predicted body
weight according to height, were the use of ventilation is
recommended between 6 mL/kg and 8 mL/kg, even further
reduced to a minimum of 4 mL/kg when possible [43]. As
Antony R Wilkes [41] says, the manufacturers are forced to
declare the range of values of VT in which the HME can be
used, therefore we suggest you to consider this information
when you have to acquire these devices in your unit.
4.3. Dead Space
One of the drawbacks of using HMEs, and which may
restrict their use, is that due to its large internal volume,
increase the dead space of the circuit, which in turn can
increase minute ventilation, carbon dioxide arterial pressure
(PaCO2) and work of breath during pressure support
ventilation [44]. This increase in dead space decreases
alveolar ventilation, and produces an increase in arterial
PaCO2, in order to maintain the same level of alveolar
ventilation. A ventilatory strategy would be to increase the
tidal volume, thereby exposing patients to induced lung
injury by volume [8]. This has a great relevance in patients
with Acute respiratory distress syndrome (ARDS), because
as described above it is important to look ventilatory
strategies of 4 mL/kg to 6 mL/kg [43]. In the study by Moran
et al, 2006 [45], in patients with acute lung injury (ALI) and
ARDS were ventilated with HME devices in which PaCO2
was measured, and then maintaining the same VT, positive
end expiratory pressure (PEEP), RR and FiO2 were changed
to a HH device, with these they saw that PaCO2 decreased
from 46 +/- 9 to 40 +/- 8 mmHg. Prat et al. [46] showed a
decrease in PaCO2 levels of 17 mmHg in patients with
ARDS when a HH are used instead of HME. This will be
related to a difference in the dead space of 95 ml between
devices [8, 46]. The reduction in dead space using HH
decreases PaCO2 and most importantly, if isocapnic
conditions are maintained through a VT reduction strategy,
which would improve lung compliance and would reduce the
plateau pressure [45].
4.4. Quantity and Quality of Airway Secretions
The presence of biofilm on the inner wall of the
endotracheal tube is represented, formed by microorganisms
that produce exopolysaccharides whose function is to protect
from antibiotics the immune system [47, 48]. This biofilm
provides the basis for the accumulation of secretions in the
tube, with the risk of further obstruction in the presence of
secretions adhered to this layer, resulting in reduced lumen at
The Open Respiratory Medicine Journal, 2015, Volume 9
107
about 7% without observing an occlusion if using a suitable
humidification. Poor moistening is associated with a high
incidence and greater degree of ETT obstruction by
secretions [49]. A proposal for the evaluation of this biofilm
it is shown in a study by Coppadoro et al. [50] through
MicroCT, where exhibits the layer of biofilm and also
stablishes that the volume of secretions in the ETT is not
associated with microbial colonization. With these data, we
can say that there is more than one risk factor that can
facilitate ETT obstruction. Branson et al. [51], based on a
series of studies, proposes some contraindications for the use
of HME, among them mentions: the presence of hematic
secretions with risk of HME occlusion, which would
increase the work breathing and adherent secretions, so more
humidification is needed to liquefy secretions and decrease
the risk of mucus plugging and airway occlusion.
4.5. Gas Exhaled Temperature
In hypothermia patients, the use of HH is recommended
because it maintains a suitable temperature in the respiratory
tract and prevents heat loss to the environment, taking a
marginal role (10%) in the elevation of body temperature
[52].
4.6. Mechanical
(VAP)
Ventilation-Associated
Pneumonia
Various authors since the 90`s, have attempted to
establish the relationship between the type of humidifier and
the rate of mechanical ventilation-associated pneumonia. In
this search, there have been randomized trials [53-55], where
Kola et al. [55] compared the hygroscopic HME and HH,
wherein show among other causes of VAP as the oropharyngeal aspiration, condensation deposited in ventilator circuits,
that by itself is a source of infection due to high levels of
colonization in the system, especially after seven or more
days of IMV. At this point we should consider incorporating
heating cable circuits to minimize the possibility of
condensation on the circuit and prevent colonization
produced by the above mentioned condensation. Other
authors, Lorente et al. 2006 [56], in the search to establish
guidelines that lead to reduced VAP, state that in periods of
IMV at least five days using HH, the incidence of VAP is
reduced when compared to HME, considering that previous
studies showed patients data with shorter periods of IMV,
and with new measures such as incorporating heating cables
circuits and servo controlled water chambers, optimum
temperature and moisture levels are achieved for the
operation of the mucociliary escalator.
In a meta-analysis of Ilias et al. (2007) [57], about the
benefits of HME compared with HH reduced: the incidence
VAP, mortality, length of ICU stay, duration of IMV, ETT
occlusions and costs associated with humidifier device. They
conclude that the available evidence does not allow
establishing differences in the performance of HME and HH
in relation to the incidence of VAP, neither in mortality,
length of ICU stay, duration of IMV or obstruction episodes.
More recently, M. Help-Martins et al. 2012 [58] found that
there are no significant differences in the use of HH and
HME on the incidence of VAP, IMV days, days of ICU stay
and overall mortality rate. In the same line, these authors
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Cerpa et al.
report in a recent meta-analysis [59] that there is insufficient
evidence to recommend the use of HME for the prevention
of VAP, due to methodological limitations in the metaanalysis as sample size, lack of any description of
randomization not mentioned in blind studies, etc.
suggesting with a degree of uncertainty that the HME does
not decrease the incidence of VAP.
Improper gas conditioning has been associated with
anatomical and functional impairment of nasal mucosa
(ciliary activity, mucus secretion, local blood flow, nasal
resistance) [64]. Epithelial metaplasia and keratinization
changes of nasal submucosa have been reported in patients
with home NIMV when the level of humidification is
inadequate for long periods of time [65].
In summary, all patients with IMV should use some
moistening and heating system. Based on some variables
such as those mentioned above and the available evidence, it
is recommended to use HH in patients with certain clinical
conditions, since the HME have certain contraindications [7,
8, 51], which are detailed below:
Especially when gas without humidifying is used in
NIMV, the upper airway can suffer mucosal dryness and
respiratory dysfunction. Leakage compensation applied by
NIMV deliver high flows throughout the respiratory cycle,
which contributes to the loss of heat and humidity [14, 66].
1.
Patients with hypothermia (body T° <32°C), since
HME occupy temperature and moisture of exhaled
gas, if this is decreased, the moisture inspired will
also decrease.
2.
Patients with hematic secretions, due to risk of
coagulation, they may occlude ETT and/or HME,
which would increase work of breathing.
3.
Patients with adherents and/or copious secretions, we
must deliver high humidity (44 mg/L and 100% RH),
to prevent the inspired gas from capturing heat and
moisture of large caliber airway drying secretions,
altering mucociliary belt, and producing mucus
plugging of the airways.
4.
Patients with leaking air, with an exhaled VT less
than 70% of VT inspired, such as bronco pleural
fistula, the entire volume of exhaled gas does not
enter the HME, thus losing heat and humidity.
5.
Patients with low VT, with protective ventilation
strategies (4-6 ml/kg), because they contribute to
increased dead space, and increase levels of PaCO2.
6.
Patients with high values of minute volume (> 10
L/min).
5. IS NECESSARY HUMIDIFICATION IN NIMV?
Evidence supports the use of NIMV in the management
of acute respiratory failure (ARF) to avoid endotracheal
intubation in patients with exacerbations of COPD or acute
cardiogenic pulmonary edema, and immunocompromised
patients as well as to facilitate extubation in patients with
COPD [60]. Although there are several aspects that provide
us a better patient-ventilator synchrony, and thus better
adherence and success of NIMV, there is a lack of evidence
that improved patient-ventilator synchrony is related to
greater success of NIMV. However, as far as the patientventilator interaction, dyspnea and comfort are related, no
one can argue against efforts to improve the synchrony
during NIMV [61]. One aspect to consider is the moistening
in patients who are undergoing NIMV. Inspiratory gases
delivered by mechanical ventilators in ICU are dry, breathing
rate is high, and mouth breathing is common during NIMV
[62]. In the presence of mouth leaks with a nasal interface,
the unidirectional flow dries upper airway and increases
nasal airway resistance. When the upper airway is dried,
increases patient discomfort, and may affect tolerance to
NIMV [63].
A recent study found that even with the same
configuration of the HH, the AH varied between subjects, as
well as increased inspiratory gas leak in some patients, AH
decreased. The oral breathing decreased oral moisture and
aggravated the feeling of dryness in patients [66].
The use of domiciliary NIMV for a few hours a day is
widely used in different pathologies, although there are no
general recommendations or guidelines for humidification
during home NIMV [66], a 40-60% of nasal CPAP users
with obstructive sleep apnea syndrome (OSA) reported nasal
congestion, dry mouth and throat pain after breathing cold
and dry air [67], which explains in detail the nasal
discomfort during CPAP treatment [68]. RH decrease can be
attenuated significantly through thermal and humidification
of inspired air, even during periods of mouth leak in patients
with OSA [69]. Based on this, the American Academy of
Sleep Medicine has recommended the use of HH to improve
adaptation and adherence to CPAP as a standard practice
[63].
In hospitalized patients there is more controversy
whether humidification is routinely required during NIMV in
acute patient care [14, 70]. Richard Branson et al. [14] says
that the controversy continues about whether if routinely
supplemental humidification is required during NIMV in
acute patients. Gas law principles and clinical experience
suggest that humidification can be used according to the
patient’s comfort and NIMV duration, and concludes that
there is insufficient evidence to support the routinary use of
active humidification during NIMV. Dean R. Hess [70]
based on his personal experience in patients with ARF, states
that an HH improves comfort and tolerance to NIMV, and
produces less dryness of upper airway. Humidification level
does not need to be so great as to an intubated patient; 100%
of relative humidity and around 30°C is usually sufficient,
higher temperatures may be less comfortable during NIMV.
Esquinas et al. [64] says that the analysis of the need for
humidification during NIMV should clearly take into
account the following parameters: Air leaks; NIMV
interface; mechanical ventilator type; room temperature;
inhaled gas temperatures and chamber vaporization; air flow
and inlet pressure of the humidification system and
humidification system type. And according to early observed
histopathological changes in nasal mucosa, by the author in a
study not yet published, in four patients with ARF, which are
treated for seven days with NIMV without a humidification
system, suggests that these nasal mucosa changes are
relatively produced after starting NIMV in an acute situation,
Humidification on Ventilated Patients
The Open Respiratory Medicine Journal, 2015, Volume 9
109
and that humidification should be considered even when a
short term NIMV use is expected.
damage to the epithelium of the respiratory tract and airway
obstruction by secretions. This entails increased respiratory
effort and alteration of the homeostasis gas exchange system.
6. ACTIVE OR PASSIVE NIMV HUMIDIFICATION?
During NIMV an inadequate gas conditioning has been
associated with anatomical and functional impairment of the
nasal mucosa. It is suggested the use of active humidification
(2B evidence), while the use of passive humidification is not
recommended (2C evidence). However recent publications
using ICU ventilators are disagree with these recommendations.
Jaber et al. refer that minute volume (VE) was
significantly greater with HME than with HH, this increase
in VE was the result of increased respiratory rate with HME
than with HH, and PaCO2 was significantly greater with
HME than with HH, and concludes that during NIMV,
increased dead space with HME can negatively affect
ventilatory function and gas exchange, this may decrease the
effectiveness of NIMV in patients with ARF [71].
Recent recommendations favor the use of heated
humidifiers (HH) during NIMV [7, 72], reducing nasal
resistance, helping expectoration and improving adhesion
and comfort, especially in patients with bronchial secretions
[72]. HME is not recommended in NIMV, because dead
space of the device has a negative impact on CO2 elimination
and minute ventilation in patients treated with NIMV in ICU,
this is more evident in hypercapnic patients [72, 73] also,
there has been seen that it increases work in breathing [65,
71]. Restrepo et al. [7] supports this by saying that the active
humidification is suggested for NIMV, because it can
improve adherence and patient comfort (2B level evidence),
and adds that the use of an HME is contraindicated in
patients in NIMV (2C level evidence) with great mask leaks,
because the patient does not exhale sufficient VT to replace
heat and humidity to an adequate inspired gas. However a
recent multicenter randomized controlled trial of 2014,
Lellouche F. et al. [62] says that no short-term physiological
benefits of HH were observed, compared with HME during
NIMV, with "ICU ventilators" (bi branch) and no differences
in the rate of intubation were found, thus concluding that the
physiological effects may have been mitigated by leaks or
other clinically important factors. Therefore states not to
support the recent recommendation for the use of HH v/s
HME during NIMV with "ICU ventilators ".
We believe that in the application of NIMV, the type of
ventilators takes an important role in the decision of the
humidifier to be used. For a single branch turbine ventilator
and with leakage compensation, it would be considered the
use of HH in patients undergoing periods greater than 24 hrs
of NIMV to enhance the feeling of oral dryness and
tolerance as recommended Oto in 2014 [66]. It is also
important to consider the recommendations of Esquinas et
al. [64] in terms of the factors involved in selecting the type
of humidification to use such as; air leakage, interface type,
type of ventilator, ambient temperature, inhaled gas
temperature among others. Taking into consideration when
using HME in single-branch NIMV, there must be taken into
account where the exhalatory port is in the system.
CONCLUSION
Humidification of the airway is required in all patients
with artificial airway and/or connected to IMV (1A
evidence). Humidification devices can be HH or HME, being
the clinical characteristics the ones that determine which
device should be chosen. It is important to select the right
system to avoid the complications of deficient
humidification, such as dryness of the respiratory mucosa,
We believe that to choose the type of humidifier to be
used during NIMV, there are some aspects that must be
taken into consideration such as the type of ventilator, the
interface type and leakage, among others, that could favor
the use of HH over HME to improve the tolerance and
patient comfort.
CONFLICT OF INTEREST
The authors declare that there are no conflict of interest.
ACKNOWLEDGEMENTS
Author’s Role: All authors helped to write the manuscript
and have seen and approved the final version. A special
thanks to Jerónimo Graf and the ICU of Clínica Alemana de
Santiago.
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