ArticlePDF AvailableLiterature Review

Humidification of inspired gases during mechanical ventilation

Authors:

Abstract

Humidification of inspired gas is mandatory for all mechanically ventilated patients to prevent secretion retention, tracheal tube blockage and adverse changes occurring to the respiratory tract epithelium. However, the debate over "ideal" humidification continues. Several devices are available that include active and passive heat and moisture exchangers and hot water humidifiers Each have their advantages and disadvantages in mechanically ventilated patients. This review explores each device in turn and defines their role in clinical practice.
496 MINERVA ANESTESIOLOGICA April 2012
R E V I E W
Anno: 2012
Mese: April
Volume: 78
No: 4
Rivista: MINERVA ANESTESIOLOGICA
Cod Rivista: Minerva Anestesiol
Lavoro:
titolo breve: Humidication of inspired gases
primo autore: GROSS
pagine: 496-502
Mechanical ventilation uses dry, piped gas
instead of room air to ventilate the lungs
which bypass the body’s normal warming and
humidifying mechanisms. Dry gas has detri-
mental eects on the respiratory tract in intubat-
ed patients, damaging epithelium and causing
secretions to become more viscous. To prevent
this occurring, several types of humidiers have
been produced for clinical use and each has its
own advantages and disadvantages.
Dening humidity
Humidity refers to the amount of water vapor
in a gaseous environment. It can be expressed in
two ways. Absolute humidity (AH) is the mass
of water in a given volume of gas, usually ex-
pressed in mg H2O/L or Kg H2O/m3.
Relative humidity (RH) is the amount of wa-
ter vapor present in a volume of gas as a percent-
age of the amount of water vapor that is required
to fully saturate the same volume of gas at the
same temperature and pressure.
e temperature must be specied, as the
maximum amount of water vapor that a volume
of gas can hold increases as temperature increas-
es. Conversely, as gas that is fully saturated with
water is cooled, the gas can no longer accommo-
date all the water vapor present and water con-
denses out onto the surroundings. A common
example of this occurs within the expiratory
limb of breathing circuits.
Humidity and heat within
the respiratory tract
Indoor atmospheric air at 20 °C has a AH of
around 10 mg H2O/L water and a RH of 55-
60%. As this air passes through the nose and up-
per airways it is warmed and moistened. In the al-
veoli, the air is at 37 °C and is fully saturated with
44 mg H2O/L water (RH=100%). is provides
optimal conditions for gas exchange at the alveo-
lar-capillary interface and is referred to as “body
temperature and pressure saturated with water va-
por” (BTPS). e airway provides both heat and
moisture to inspired air to meet these conditions.
Heat losses may result as heat energy is ex-
Humidication of inspired gases
during mechanical ventilation
J. L. GROSS, G. R. PARK
Intensive Care Unit, North Middlesex, University Hospital, Sterling Way, London, UK
ABSTRACT
Humidication of inspired gas is mandatory for all mechanically ventilated patients to prevent secretion retention,
tracheal tube blockage and adverse changes occurring to the respiratory tract epithelium. However, the debate over
“ideal” humidication continues. Several devices are available that include active and passive heat and moisture ex-
changers and hot water humidiers Each have their advantages and disadvantages in mechanically ventilated patients.
is review explores each device in turn and denes their role in clinical practice. (Minerva Anestesiol 2012;78:496-502)
Key words: Respiration, articial - Humidity - Tracheostomy.
HUMIDIFICATION OF INSPIRED GASES GROSS
Vol. 78 - No. 4 MINERVA ANESTESIOLOGICA 497
pended to convert liquid moisture within the
airway epithelium to vapor (latent heat of va-
porisation) and by direct transfer of heat from
mucosa to incoming air.
Eects of inadequate humidication
Inadequate humidication causes increased
mucus viscosity and inspissation, depressed cili-
ary function, tracheal inammation and mucosal
ulceration. Later changes include epithelial cell
necrosis and squamous metaplasia. ese changes
may result in an increased incidence of respira-
tory tract infection and airway obstruction or at-
electasis due to retained secretions. Additionally,
as the body tries to humidify dry gas, there is an
increased loss of body water and heat. Although
this may be of insignicant consequence in adults,
it may have important clinical implications in
children, particularly neonates who have a higher
minute ventilation to body surface area ratio. Bis-
sonnette et al.1 showed a reduction in core body
temperature of 0.75 °C in anesthetised children
after 90 minutes in those not receiveing any form
of humidication compared with those who did.
Hypothermia has many adverse eects. Amongst
these, ventilation with cold dry gases may cause
deterioration in FEV1 of up to 21% in asthmatic
patients and a less favorable improvement in FEV1
in non-asthmatic patients that would normally
occur in warm humid conditions.2 is may re-
sult in greater work of breathing and impair wean-
ing from mechanical ventilation.
Eects of over humidication
Currently, there are no criteria for over-hu-
midication. In some reports, it has been sug-
gested that over humidication occurs when tra-
cheal gas is fully saturated above around 32 °C,
a point where water vapor content is higher dur-
ing inspiration than expiration and exchanges of
heat and water are reversed during a respiratory
cycle.3 Others suggest over-humidication oc-
curs when delivered inspired gas is above BTPS.4
Overhumidication reduces mucus viscosity,
increases the pericillary layer, dilutes surfactant
and causes neutrophilic inltration of lungs and
bronchioles. e resulting eect of these changes
causes secretion retention, atelectasis, worsening
lung compliance, increased pulmonary shunt
fraction with an increased alveolar-arterial oxy-
gen gradient.4 ese changes may result in pul-
monary and generalized edema, weight gain,
hyponatremia and increased local susceptibility
to bacterial invasion leading to bronchopneu-
monia. Delivering inspired over-humidied gas
may cause water to condense on the walls of the
breathing circuit resulting in increased airow re-
sistance with further potential for infection from
retained droplets. Problems with under and over
humidication are summarised in Table I.
Eects of excess heat
Overheating the respiratory tract causes mu-
cosal sloughing, impairment of mucociliary
clearance and deposition of brin casts in small
airways. is results in mechanical obstruction
leading to carbon dioxide retention and impaired
oxygenation with ventilation-perfusion mis-
match. e temperature at which these changes
occur is also dependent on humidity and dura-
tion of exposure, but it has been recommended
that respiratory gases that arrive at the tracheal
end of the endotracheal tube should average less
T I.—Summary of the adverse eects of under and over humidication.
Ia
Eects of dry gas inhalation
Ib
Eects of excess pulmonary water delivery
Mucosal ulceration
Destruction of cilia
Hyperaemia and inammation
Desquamation of cells
Disorganisation of basement membrane and epithelial layer
Cytoplasmic and nuclear degeneration
Microatelectasis from obstruction of small airways and
reduced surfactant leading to reduced lung compliance
Excessive pulmonary secretions
Edema (pulmonary and generalized)
Weight gain
Hyponatremia
Decreased pulmonary compliance
Reduced vital capacity
Lowered alveolar-arterial oxygen gradient
GROSS HUMIDIFICATION OF INSPIRED GASES
498 MINERVA ANESTESIOLOGICA April 2012
H20/L. is nding has been replicated else-
where.10 While some manufacturers use the
gravimetric method to test performance (as
used by the international standard ISO 9360 11)
which involves weighing the humidier before
and after the period of operation under strictly
controlled conditions, others use the psychro-
metric method.
Although there is little discrepency between
both methods in vitro,6, 7 only a psychrometric
test can be used in patients and future devices
should be benchmarked against this technique
in vivo.
Current evidence suggests that p-HMEs that
can deliver gases with an AH >30 mg H20/L
have a low risk of tracheal tube occlusions while
those providing AH of <25 mg H20/L are associ-
ated with a signicant increase in tracheal tube
occlusion and should be avoided.6 Providing AH
between 25 and 30 mg H20/L is considered a
“grey zone” and those using a device providing
this range of AH, should consider to the risk of
tracheal tube occlusion. In terms of durability,
manufacturers recommend that p-HMEs are
changed every 24 hours, but providing an AH
>30 mgH20/L is achieved and maintained, the
life-span of these devices could be extended to
48 hours 12 or even as long as one week in certain
patients without any increase in the risk of tra-
cheal tube occlusion or bacterial colonisation.9
However, further testing of devices that consist-
ently achieve AH levels >30 mg H20/L in vivo
and determining the durability of each device
are needed.
Active heat and moisture exchangers
Active heat and moisture exchangers (a-
HMEs) include a regular HME, but place a
small heater between the HME and the patient
that vaporises added water.
e Humid-Heat® device (Gilbeck AB, Swe-
den) allows water to drip onto a heated paper
element that acts as a wick. e HME Booster®
(Medisize, Belgium) features a heater covered
with a Gore-Tex® membrane. Water is added to
the surface of the heater and vaporised, allowing
passage through the membrane, that regulates
the amount of water vaporised. Both devices
than 42 °C to prevent the adverse eects associ-
ated with thermal injury.5
Methods of humidication
Passive heat and moisture exchangers
Passive heat and moisture exchangers (p-
HME) sit between the tracheal tube and ventila-
tor tubing and work by trapping heat and mois-
ture as a patient expires and returning them to
the patient in the next inspiration. Because all
heat and moisture is derived entirely from the
patient and no energy is added to the system this
is a passive system. Under optimal conditions
they can provide up to 30-32 mgH2O/L AH
at 27-30 °C 6 but their ultimate performance is
dependent on a number of factors such as ambi-
ent temperature, inspiratory and expiratory ow
rates, surface area and water vapour content of
the medium.
ey are composed of material of high ther-
mal capacity and conductivity that is arranged in
a spun and pleated fashion to allow gas to cool
and condense on expiration and warm and evap-
orate on inspiration. Some have a hygroscopic
element, usually calcium or lithium chloride,
which improves water retention following expi-
ration and hence improveseciency.7
Despite the theoretical advantages of hygro-
scopic p-HMEs compared with hydrophobic de-
vices no dierences were shown in the quantity
of tracheal aspirates, mucus viscosity, atalectasis,
tracheal tube occlusion, bacterial colonization
and ventilator associated pneumonia (VAP).8
Studies looking at dierent types of p-HMEs,
have been shown to vary considerably in terms
of performance and durability.6, 7, 9 Some devices
perform sub-optimally leading to increased air-
way resistance and tracheal tube occlusion from
retained secretions. Lellouche et al.6 independ-
ently tested the performance of 48 p-HMEs
and showed only 37.5% performed well (AH
≥30 mgH20/L) with 25% performing poorly,
providing AH <25 mgH20/L, a level associated
with tracheal tube occlusion. Furthermore, there
was a signicant discrepancy between the meas-
ured AH and the manufacturers data, where in
36% of devices the dierence of AH was >4 mg
HUMIDIFICATION OF INSPIRED GASES GROSS
Vol. 78 - No. 4 MINERVA ANESTESIOLOGICA 499
wires within the walls of the tubing. e risk of
colonisation may also be reduced by increasing
the temperature of the water bath up to 45-60
°C (continuous Pasteurisation),17 adding anti-
bacterial agents to the water or breathing circuit
tubing 18 or maintaining a closed sterile system.
Increasing temperature poses an increased risk of
inhalational thermal injury. Antibacterial agents
are rarely used due to the risk of ingestion and
maintaining a closed sterile system is dicult to
achieve. Unless visibly soiled, breathing circuits
need not be replaced routinely 19 and unneces-
sary manipulations and breaks in circuit tubing
should be avoided.
Choice of humidier
Although providing some sort of humidica-
tion is essential in mechanically ventilated pa-
tients, it is still unknown what device is most
benecial. Table II summarises each device.
e ideal humidier should provide optimal
temperature and humidication with low risk
of adverse events, be simple to use and inexpen-
sive. One reason for lack of such a device is that
the optimal level of humidity and temperature
is still unknown. Standards for humidiers for
medical use state that p-HMEs should provide
at least 30 mgH2O/L at 30 °C when tested at
tidal volumes greater that 250 mL (ISO 936011)
and that HWHs should be able to provide at
least 33 mgH2O/L with maximum respirato-
ry gas temperature not exceeding 42 °C (ISO
81855). However, these standards are based on
in-vitro testing and set a minimum perform-
ance for humidiers, but do not dene a level of
humidication that provides maximum clinical
benet.
While p-HMEs provide AH of up to 32 mg
H2O/L at 27-30 °C, HWHs and the newer a-
HMEs can provide AH close to 44 mg H2O/L
at 37 °C. Providing such conditions with HWH
and a-HMEs may not be necessary and can re-
sult in over-humidication and heat related
airway injury.20 Both p-HMEs and a-HMEs
can become occluded with blood, secretions or
condensate resulting in an increased resistance
to airow and work of breathing. In hypother-
mic patients p-HMEs and possibly a-HMEs
have the advantage that should they run dry, the
HME functions normally.
In vitro studies comparing a-HMEs with pas-
sive devices have consistently shown increased
inspired AH with airway temperature ranging
from 31.9 to 37 °C and AH from 34.3 to 44 mg
H2O/L.13-15 Similar results have been produced
in-vivo, where the same device (the Performer)
provided signicantly higher levels of humidi-
cation (AH range 30-36 mg H20/L) when used
as an active device compared with its use as a
passive device.14 In the same study, whilst the
ecacy of p-HMEs worsened at minute venti-
lation both above or below 10 L/min, a-HMEs
retained their function suggesting these devices
may be more suitable for extremes of minute
ventilation. Others have shown that the aHME
retains its eciency between 3 and 25 L/min.15
In hypothermic conditions, Pelosi et al. dem-
onstrated that a-HMEs perform better, provid-
ing AH of 27.1 mg H2O/L compared with 24.6
mg H20/L from the best performing passive de-
vice when expired airway temperature was 28
°C.13 Overall, data for a-HMEs looked promis-
ing at rst but has not translated into widespread
clinical use.
Hot water humidiers
Hot water humidiers (HWH) have tradi-
tionally been considered to be the gold standard
in providing humidication as they deliver gas at
37 °C with an AH of 44 mg H2O/L, but in clini-
cal use may only deliverAH levels between 35 and
40 mg H2O/L.16 ey have a heating element,
which heats the water within a chamber. Dry gas
is then passed through this chamber, over the
hot liquid surface or bubbled through the water
to become humidied. e temperature with-
in the chamber is thermostatically controlled
which allows fully saturated gas to be produced
at a variety of temperatures. It is more ecient in
providing humidication when compared to p-
HMEs, but the risks and costs are greater. Risks
include overheating, causing inhalational burns
and the possibility of water condensing within
the inspiratory limb of ventilator tubing as gas
cools, which may lead to bacterial colonisation.
is may be reduced by incorporating heated
GROSS HUMIDIFICATION OF INSPIRED GASES
500 MINERVA ANESTESIOLOGICA April 2012
HMEs daily in accordance to manufacture rec-
ommendations. Studies showing safe use of p-
HMEs beyond the 24 hour period 12 should be
repeated and if p-HMEs can be used safely for
more prolonged periods, such as up to 48 hours,
it would represent a major cost advantage for p-
HMEs over HWHs.
Several meta-analyses have shown no dier-
ence in VAP rates or airway occlusion between
HMEs and HWHs.26, 27 ere were also no dif-
ferences seen with respect to atelectasis, PaCO2,
work of breathing, secretion clearance and
length of ICU stay.27 e only dierences ob-
served were a lower body temperature and lower
cost in the p-HME group.
ere is not one method of humidication
that is universal for every patient in every situa-
tion, so the choice of device should be tailored to
the individual patient. A number of algorithms
have been developed to aid choice of humidier
in each situation. One suggested example was
developed by Branson et al. at the University of
Cincinnati 28 (Figure 1).
In this study, the quality of pulmonary secre-
tions aspirated by suction catheter was used as
a measure of adequacy of humidication, based
on the scale described by Suzukawa et al.29 (Ta-
ble III). e algorithm was evaluated in 120 pa-
tients and was shown to be cost eective and safe
in one surgical ICU.
have limited performance and should be used
with caution, while HWHs can potentially
lead to over-humidication.20 e American
Association of Respiratory Care guidelines sug-
gest p-HMEs should be avoided for patients
with body temperature less than 32 °C.21 Both
active and passive HMEs should also be used
cautiously with patients undergoing low tidal
volume ventilation (such as in acute respiratory
distress syndrome) as HMEs increase dead space
by up to 90 mL, which may increase the risk of
hypercapnia.22 Similarly, HMEs should not be
used for patients with an expired tidal volume
less than 70% the delivered tidal volume (e.g.
those with large bronchopleurocutaneous stu-
las or incompetent or absent tracheal tube cus)
21 nor should they be used in dicult to wean
patients with chronic respiratory failure, such
as chronic obstructive pulmonary disease.23 P-
HMEs may also be contraindicated in patients
with high minute volumes exceeding 10 L/min
as they have reduced ecacy.23, 24
In some situations the choice of humidica-
tion method may be inuenced by cost eective-
ness. Boots et al. in 2006 evaluated daily cost
of p-HME compared with HWHs, taking into
account purchasing and maintenance costs.25
e daily cost of p-HMEs were comparable to
HWHs (AUS $ 8.62 vs. AUS $ 8.98, respec-
tively). ese costings were based on changing
T II.—Comparison of dierent types of humidiers.
Advantages Disadvantages
Cold water humidier Simple
Cheap
Inadequate humidity
Infection risk
Nebuliser device Suitable for high frequency jet ventilation Risk of over humidication, hypothermia and infection
Passive HME device Simple
Cheap
Provides adequate humidity for many patients
Increased dead space
Increased circuit resistance
Risk of obstruction
Inadequate in some cases
Active HME device Relatively simple
Relatively cheap
Boosted humidity output compared to HME.
Still performs as pHME if allowed to run dry
Increased dead space
Increased circuit resistance
Risk of obstruction
Hot water humidier Delivers maximal humidication at 37 °C Complex to setup and run
Expensive to acquire and maintain
Risk of infection
Risk of aspiration of water
Risk of burns/electric sock
Over-humidication possible
Large number of connection to become disconnected
HUMIDIFICATION OF INSPIRED GASES GROSS
Vol. 78 - No. 4 MINERVA ANESTESIOLOGICA 501
nose and mouth dryness) which may contribute
to NIV failure.30 Secondly, If NIV fails as a re-
sult of insucient humidication, subsequent
tracheal intubation may be more dicult ow-
ing to mucosal drying and secretion retention.31
Lellouche et al.30 studied the impact of HMEs
and HWHs in normal volunteers exposed to
NIV in the presence and absence of mask leak
for one hour. No humidication provided an
AH of around 5 mg H2O/L, while use of either
an HME or HWH provided AH of inspired
gases to between 25-30 mg H2O/L. In the pres-
ence of mask leaks the AH of delivered dry gas
decreased to 15 mgH2O/L with HMEs but was
maintained at 30 mg H2O/L with HWHs. Be-
cause of inevitable air leaks which occur around
the mask, the gas ow associated with NIV is
mostly unidirectional and therefore the amount
of heat and moisture that can be exchanged
with HMEs is reduced. However, using HMEs
during NIV increases work of breathing be-
cause of the additional dead space added to the
circuit.32, 33 Although humidication should be
provided, HWHs should be used in preference
to HMEs. ese factors may decrease patient
adherence to therapy and ultimately cause NIV
failure.32, 33
Conclusions
e devices most suited for humidication
include the HWH, the p-HME and more re-
cently the a-HME. e HWH and a-HME
undoubtedly provide higher humidity levels for
inspired gas but in some patients, p-HMEs may
have advantages. ere is no one method of hu-
midication that suits all patients and clinicians
need to tailor the method used to the patient’s
needs.
Humidication during non-
invasive ventilation
Gas delivered when using non-invasive venti-
lation (NIV) passes through the upper airways
and is exposed to the body’s normal humidify-
ing system. Despite this there is increasing evi-
dence that additional humidication is needed.
Firstly, patient comfort is key to NIV success
and not providing additional humdication sig-
nicantly reduces patient comfort levels (mostly
Figure 1.—Algorithm to aid choice of humidication (devel-
oped by Branson et al.28). HCH: hygroscopic condenser hu-
midier (equivalent to p-HME).
T III.—Grading of secretions aspirated with suction catheter.
Type of secretion Description
in Suction catheter clean after use
Moderate Secretions adhere to inside of catheter after suctioning but are easily cleared by aspirating water
ick Secretions adhere to inside of catheter after suctioning, but cannot be cleared by aspirating water
Reproduced from Suzukawa et al.29
GROSS HUMIDIFICATION OF INSPIRED GASES
502 MINERVA ANESTESIOLOGICA April 2012
18. Yousefshahi F, Khajavi MR, Anbarafshan M, Khashayar P,
Naja A. Sanosil, a more eective agent for preventing the
hospital-acquired ventilator associated pneumonia. Int J
Health Care Qual Assur 2010;23:583-90.
19. Long MN, Wickstrom G, Grimes A, Benton CF, Belcher
B, Stamm AM. Prospective, randomized study of ventila-
tor-associated pneumonia in patients with one versus three
ventilator circuit changes per week. Infect Control Hosp
Epidemiol 1996;17:14-9.
20. Lellouche F, Qader S, Taille S, Lyazidi A, Brochard L. Un-
der humidication and overhumidication during moder-
ate induced hypothermia with usual devices. Intens Care
Med 2006;32:1014-21.
21. AARC Clinical Practice Guideline: Humidication during
mechanical ventilation. Respir Care 1992;37:887-90.
22. Prat G, Renault A, Tonnelier J-M, Goetghebeur D, Oger E,
Boles JM et al. Inuence of the humidication device dur-
ing acute respiratory distress syndrome. Intens Care Med
2003;29:2211-5.
23. Girault C, Breton L, Richard JC, Tamion F, Vandelet P,
Aboab J et al. Mechanical eects of airway humidica-
tion devices in dicult to wean patients. Crit Care Med
2003;31:1306-11.
24. Martin C, Ppazian L, Perrin G, Bantz P, Gouin F. Perform-
ance evaluation of three vaporizing humidiers and two
heat and moisture exchangers in patients with minute ven-
tilation >10 L/min. Chest 1992;102:1347-50.
25. Boots RJ, George N, Faoagali JL, Druery J, Dean K, Hel-
ler RF. Double-heater-wire circuits and heat-and-moisture
exchangers and the risk of ventilator associated pneumonia.
Crit Care Med 2006;34:687-93.
26. Siempos II, Vardakas KZ, Kopterides P, Falagas M. Impact
of passive humidication on clinical outcomes of mechani-
cally ventilated patients: A meta-analysis of randomized
controlled trials. Crit Care Med 2007;35:2843-51.
27. Kelly M, Gillies D, Todd DA, Lockwood C. Heated hu-
midication versus heat and moisture exchangers for venti-
lated adults and children. Cochrane Database of Systematic
Reviews 2010, issue 4.
28. Branson RD, Davis K, Jr, Campbell RS, Johnson DJ, Po-
rembka DT. Humidication in the intensive care unit.
Prospective study of a new protocol utilizing heated hu-
midication and a hygroscopic condenser humidier. Chest
1993;104:1800-5.
29. Suzukawa M, Usada Y, Numata K. e eect of sputum
characteristics of combining an unheated humidier with a
heat-moisture exchanging lter. Resp Care 1989;34:976-84.
30. Lellouche F, Maggiore SM, Lyazidi A, Deye N, Taille S,
Brochard L. Water content of delivered gases during non-
invasive ventilation in healthy subjects. Intens Care Med
2009;35:987-95.
31. Esquinas A, Nava S, Scala R, Carrillo A, Gonzalez Diaz G,
Artacho R et al. Humidication and dicult endotracheal
intubation in failure of noninvasive mechanical ventilation.
Preliminary results (abstract). Am J Respir Crit Care Med
177:A644.
32. Lellouche F, Maggiore SM, Deye N, Taille S, Pigeot J,
Harf A et al. Eect of humidication device on the work of
breathing during noninvasive ventilation. Intens Care Med
2002;28:1582-9.
33. Jaber S, Chanques G, Matecki S, Ramonatxo M, Souche B,
Perrigault PF et al. Comparison of the eects of heat and
moisture exchangers and heated humidiers on ventilation
and gas exchange during non-invasive ventilation. Intens
Care Med 2002;28:1590-4.
References
1. Bissonnette B, Sessler DI, LaFlamme P. Passive and active
inspired gas humidication in infants and children. An-
esthesiology 1989;71:350-4.
2. Eschenbacher WL, Moore TB, Lorenzen TJ. Pulmonary
response of asthmatic and normal subjects to dierent
temperature and humidity conditions in an environmental
chamber. Lung 1992;170:51-62.
3. Sottiaux TM. Consequences of under- and over humidica-
tion. Respir Care Clin 2006;12:233-52.
4. Williams RB, Rankin N, Smith T, Galler D, Seakins P.
Relationship between the humidity and temperature of in-
spired gas and the function of the airway mucosa. Crit Care
Med 1996;24:1920-9.
5. International Organization for Standardization. Hu-
midiers for Medical Use – Safety Requirements (ISO
8185:1988). Geneva: International Organization for Stand-
ardization, 1988.
6. Lellouche F, Taille S, Lefrancois F, Deye N, Maggiore SM,
Jouvet P et al. Humidication performance of 48 passive
airway humidiers. Comparison with manufacture data.
Chest 2009;135:276-86.
7. Branson RD, Davis K. Evaluation of 21 passive humidiers
according to the ISO 9360 standard: Moisture output, dead
space and ow resistance. Respir Care 1996;41:736-43.
8. omachot L, Viviand X, Arnaud S, Boisson C, Mar-
tin CD. Comparing two heat and moisture exchangers,
one hydrophobic and one hygroscopic, on humidifying
ecacy and the rate of nosocomial pneumonia. Chest
1998;114:1412-8.
9. Ricard JD, Le Miere E, Morkowicz P, Lasry S, Saumon G,
Djedaini K et al. Eciency and safety of mechanical venti-
lation with heat and moisture exchanger changed only once
a week. Am J Respir Crit Care Med 2000;161:104-9.
10. Guillaume T, Boyer A, Etienne P, Salah, A, de Lassence
A, Dreyfuss D et al. Heat and moisture exchangers in me-
chanically ventilated intensive care unit patients: A plea for
an independent assessment of their performance. Crit Care
Med 2003;31:699-704.
11. International Organisation for Standardisation. Anaesthetic
and Respiratory Equipment – Heat and Moisture Exchang-
ers for Use in Humidifying Respired Gases in Humans. Ge-
neva: International Organisation for Standardisation Tech-
nical Committee 1992 International Standard ISO 9360,2.
12. omachot L, Vialet R, Viguier JM, Benjamin S, Roulier
P, Claude M. Ecacy of heat and moisture exchangers after
changing every 48 hours rather than 24 hours. Crit Care
Med 1998;26:477-81.
13. Pelosi P, Severgnini P, Selmo G, Corradini M, Chiaranda
M, Novario R et al. In vitro evaluation of an active heat-
and-moisture exchanger: the Hygrovent Gold. Respir Care
2010;55:460-6.
14. Chiumello D, Pelosi P, Park G, Candiani A, Bottino N,
Strorelli E. In vitro and in vivo evaluation of a new active
heat moisture exchanger. Crit Care 2004;8:R281-R8.
15. Larsson A, Gustafsson A, Svanborg L. A new device for 100 per
cent humidication of inspired air. Crit Care 2000;4:54-60.
16. Lellouche F, Taille S, Maggiore SM, Qader S, L’Her E, Dey
N et al. Inuence of ambient and ventilator output tem-
peratures on performance of heated wire humidiers. Am J
Respir Crit Care Med2004;170:1073-9.
17. Redding PJ, McWalter PW. Pseudomonas uorescence
cross infection due to contaminated humidier water. Br
Med J 1980;281:275.
Conicts of interests.—GRP Consults to Inspired Technologies Ltd, who design novel active heat and moisture exchanging humidiers.
Received on March 31, 2011. - Accepted for publication on January 11, 2012.
Corresponding author: G. R. Park, North Middlesex Hospital, Sterling Way, London, UK. E-mail: gilbertpark@me.com
is article is freely available at www.minervamedica.it
... In one of the earliest prototypes of positive pressure ventilators, such as the Morch's respirator (1954), a humidifier was already incorporated [1,2]. Indeed, the necessity to heat and humidify gases in ventilated patients became evident early due to the observed injuries caused by compressed medical gases during invasive mechanical ventilation [3]. ...
... The importance of humidifying medical gases during ventilation is well established in Intensive Care Units (ICUs) [3]. In the past, aerosol-based devices were commonly used. ...
Article
Full-text available
The humidification process of medical gases plays a crucial role in both invasive and non-invasive ventilation, aiming to mitigate the complications arising from bronchial dryness. While passive humidification systems (HME) and active humidification systems are prevalent in routine clinical practice, there is a pressing need for further evaluation of their significance. Additionally, there is often an incomplete understanding of the operational mechanisms of these devices. The current review explores the historical evolution of gas conditioning in clinical practice, from early prototypes to contemporary active and passive humidification systems. It also discusses the physiological principles underlying humidity regulation and provides practical guidance for optimizing humidification parameters in both invasive and non-invasive ventilation modalities. The aim of this review is to elucidate the intricate interplay between temperature, humidity, and patient comfort, emphasizing the importance of individualized approaches to gas conditioning.
... 7 La humidificación del aire inspirado durante la AMV debe cumplir con garantizar la temperatura y humedad adecuadas, humedad alrededor de 44 mg/L y temperatura corporal a 37°C y evitar la posibilidad de contaminación de la vía respiratoria. 8,9 ...
... During mechanical ventilation (via endotracheal tube (ETT) or tracheostomy) the upper airway is bypassed and the body's ability to heat and humidify inhaled gases is impaired. Dehumidified gas has numerous detrimental effects on the airways distal to the bronchioles and the function of the mucociliary elevator, including increased mucus viscosity, decreased ciliary function and tracheal inflammation [6]. The adverse effects of dry gas inhalation have also been shown to increase the risk of post-operative respiratory complications in surgical patients [7], highlighting the importance of complete inspired gas humidification during prolonged ventilation in critical care. ...
Article
Full-text available
Introduction Heat and moisture exchanger (HME) filters are commonly used as passive circuit humidifiers during mechanical ventilation, however, are only ~80% efficient. As a result, patients that undergo mechanical ventilation in critical care with HME filter circuits will be exposed to partial airway humidification. This is associated with detrimental effects including increased secretion load which has been shown to be an independent predictor of failed extubation. Nebulised normal saline is commonly utilised to supplement circuit humidification in ventilated patients with high secretion loads, although there are no randomised control trials evaluating its use. Novel vibrating mesh nebulisers generate a fine aerosol resulting in deeper lung penetration, potentially offering a more effective means of nebulisation in comparison to jet nebulisers. The primary aim of this study is to compare the viscosity of respiratory secretions after treatment with nebulised normal saline administered via vibrating mesh nebuliser or jet nebuliser. Methods and analysis This randomised controlled trial is enrolling 60 mechanically ventilated adult critical care patients breathing on HME filter circuits with high secretion loads. Recruited patients will be randomised to receive nebulised saline via 3 modalities: 1) Continuous vibrating mesh nebuliser; 2) Intermittent vibrating mesh nebuliser or 3) Intermittent jet nebuliser. Over the 72-hr study period, the patients’ sputum viscosity (measured using a validated qualitative sputum assessment tool) and physiological parameters will be recorded by an unblinded assessor. A median reduction in secretion viscosity of ≥0.5 on the qualitative sputum assessment score will be deemed as a clinically significant improvement between treatment groups at analysis. Discussion At the conclusion of this trial, we will provisionally determine if nebulised normal saline administered via vibrating mesh nebulisation is superior to traditional jet nebulisation in terms of reduced respiratory secretion viscosity in intubated patients. Results from this pilot study will provide information to power a definitive clinical study. Trial registration ClinicalTrails.Gov Registry (NCT05635903).
... Part two: "Tracheobronchial secretion assessment": This part was adopted from (Gross &Park, 2012). That involved three types of secretion viscosity thin, moderate and thick. ...
Article
Rationale: Tracheal diverticulum is a rare airway-related particular occurrence, and the forcible tube insertion may cause tracheal ruptures during tracheotomy. Therefore, fiberoptic bronchoscopy (FOB) should be used routinely on all patients undergoing tracheal intubation or tracheotomy. Patient concerns: A 60-year-old male with laryngeal neoplasms was scheduled for partial laryngectomy using a suspension laryngoscope in July 2020. All operations were performed under general anesthesia through orotracheal intubation. Orotracheal intubation was a noninvasive procedure that could effectively control breathing. At the end of the surgery, the percutaneous tracheostomy was performed to maintain airway patency, facilitate spontaneous respiration, and remove the secretions. Diagnoses: At this moment, the tracheal diverticulum, located at the right posterolateral region of the trachea, became an unexpected airway-related particular occurrence, which led to tracheal tube placement difficulty, mechanical ventilation difficulty, and high airway pressure. Interventions: Subsequently, the tracheal tube was repositioned, with placement again confirmed by the FOB. Lessons subsections: Tracheal diverticulum is an infrequent cause of tube inserting difficulty for the tracheotomy, and FOB is the first option for patients with catheter placement difficulty and mechanical ventilation difficulty.
Chapter
Noninvasive ventilation (NIV) has become a standard of care in the management of acute and chronic respiratory failure. Humidification during invasive ventilation is now a standard practice, while there is no consensus about its role in NIV. Dry air inhalation while using NIV can provoke some detrimental effects on airway mucosa. Humidification during NIV has been shown to prevent these effects and might improve tolerance and adherence. Although heated humidifiers are recommended over heat-and-moisture exchangers (HMEs) by current guidelines, the use of HMEs with low dead space seems to be acceptable. Patient comfort is of paramount in ensuring adherence to domiciliary noninvasive ventilation (NIV) or in hospital critical care ventilator.In this chapter, we summarize the effects of dry air inhalation during NIV, factors worsening these effects, various types of humidifiers, and current recommendations for humidification, while in the second part we will discuss the basics of aerosol therapy during NIV and various recommendations about how to use it efficiently.KeywordsChronic obstructive pulmonary diseaseAcute respiratory failureNoninvasive ventilationBronchial secretionNasal resistanceHumidification
Article
Background: The spontaneous breathing trial (SBT) is the final step of weaning from invasive mechanical ventilation. An SBT is aimed at predicting work of breathing (WOB) after extubation and, most importantly, a patient's eligibility for extubation. The optimal SBT modality remains debated. A high-flow oxygen (HFO) has been tested during SBT in clinical study only, which is why no definite conclusion can be drawn on its physiologic effects on the endotracheal tube. Our objective was to assess, on a bench, inspiratory tidal volume (VT), total PEEP, and WOB across 3 different SBT modalities: T-piece, 40 L/min HFO, and 60 L/min HFO. Methods: A test lung model was set with 3 conditions of resistance and linear compliance, 3 inspiratory efforts (low, normal, and high), each at 2 breathing frequencies (low and high for 20 and 30 breaths/min, respectively). Pairwise comparisons and a quasi-Poisson generalized linear model that compared SBT modalities were performed. Results: Inspiratory VT, total PEEP, and WOB differed from one SBT modality to another. Inspiratory VT remained higher with the T-piece than in the HFO independent of the mechanical condition, effort intensity, and breathing frequency (P < .001 in each comparison). WOB adjusted by the inspiratory VT was significantly lower during SBT performed with an HFO than when performed with the T-piece (P < .001 in each comparison). The total PEEP was significantly higher in the HFO at 60 L/min than in the other modalities (P < .001). The end points were significantly influenced by breathing frequency, effort intensity, and mechanical condition. Conclusions: With the same effort intensity and breathing frequency, inspiratory VT was higher in the T-piece than in the other modalities. Compared with the T-piece, WOB was significantly lower in the HFO condition and higher flow was a benefit. Based on the results of the present study, the HFO as an SBT modality would seem to require clinical testing.
Chapter
Inadequate humidification during noninvasive ventilation (NIV) is associated with some adverse outcomes. Humidification during NIV can prevent these effects and might improve patient compliance, comfort, and adherence. There is no clear consensus regarding humidification use during NIV and humidification settings. This chapter reviews studies evaluating the use of humidification in NIV and summarizes the effects of insufficient gas conditioning during the NIV procedure, the factors associated with worsening of those effects, and the recommendations for artificial humidification based on available data.KeywordsNoninvasive ventilationContinuous positive airway pressureHumidificationHeat and moisture exchangerHeated humidifier
Chapter
Airway humidification is recommended on every patient receiving invasive mechanical ventilation (MV)—by the fact that MV suppresses the mechanisms that heat and moisturize inhaled air, humidification is of utmost importance to prevent hypothermia, disruption of the airway epithelium, bronchospasm, atelectasis, and airway obstruction.Two systems are available for warming and humidifying gases delivered to patients who are mechanically ventilated: active humidification, through a heated humidifier (HH), and passive humidification, through a heat and moisture exchanger (HME). HH actively operates to increase the heat and water vapor content of inspired gas. HMEs operate passively by storing heat and moisture from the patient’s exhaled gas and releasing it to the inhaled gas.There is no consensus regarding the best humidification system—the choice should be made according to the clinical context, trying to avoid possible complications, and reaching the appropriate performance.This chapter aims to describe the basic principles of airway humidification on mechanically ventilated patients and the most used humidifier devices and define their role in clinical practice.KeywordsHumidificationInvasive mechanical ventilationHeat and moisture exchangersActive humidificationPassive humidification
Article
Full-text available
The aim of this study is to compare the effects of Sanosil and glutaraldehyde 2 percent in disinfecting ventilator connecting tubes in an intensive care unit (ICU) environment. The 12-week open-labelled clinical trial was conducted in the surgical ICU of a teaching hospital from March to May 2005. In the first phase of the study, high level disinfection was performed using glutaraldehyde 2 percent, whereas Sanosil was used as the disinfectant agent of the second phase. Samples for microbial culture were obtained from the Y piece, the expiratory limb proximal to the ventilator and the humidifier in different stages; the results were then compared. Positive culture was more frequently reported in Y pieces, humidifiers and expiratory end of ventilators. Comparing the two groups, there were more positive cultures in the glutaraldehyde group (p value = 0.005); multiple organism growths, gram negative, gram positive and fungi were also more frequent in this group (p value = 0.01; 0. 007; 0. 062; 0.144, respectively). The paper shows that Sanosil is an effective agent in reducing the contamination risk in the tubes used in ICUs.
Article
Full-text available
To improve the heat and humidification that can be achieved with a heat-and-moisture exchanger (HME), a hybrid active (ie, adds heat and water) HME, the Hygrovent Gold, was developed. We evaluated in vitro the performance of the Hygrovent Gold. We tested the Hygrovent Gold (with and without its supplemental heat and moisture options activated), the Hygrobac, and the Hygrovent S. We measured the absolute humidity, using a test lung ventilated at minute volumes of 5, 10, and 15 L/min, in normothermic (expired temperature 34 degrees C) and hypothermic (expired temperature 28 degrees C) conditions. We also measured the HMEs' flow resistance and weight after 24 h and 48 h. In its active mode the Hygrovent Gold provided the highest absolute humidity, independent of minute volume, in both normothermia and hypothermia. The respective normothermia and hypothermia absolute humidity values at 10 L/min were 36.3 + 1.3 mg/L and 27.1 + 1.0 mg/L with the active Hygrovent Gold, 33.9 + 0.5 mg/L and 24.2 + 0.8 mg/L with the passive Hygrovent Gold, 33.8 + 0.56 mg/L and 24.4 + 0.4 mg/L with the Hygrobac, and 33.9 + 0.8 mg/L and 24.6 + 0.6 mg/L with the Hygrovent S. The efficiency of the tested HMEs did not change over time. At 24 h and 48 h the increase in weight and flow resistance was highest in the active Hygrovent Gold. The passive Hygrovent Gold provided adequate heat and moisture in normothermia, but the active Hygrovent Gold provided the highest humidity, in both normothermia and hypothermia.
Article
Full-text available
No clear recommendation exists concerning humidification during non-invasive ventilation (NIV) and high flow CPAP, and few hygrometric data are available. We measured hygrometry during NIV delivered to healthy subjects with different humidification strategies: heated humidifier (HH), heat and moisture exchanger, (HME) or no humidification (NoH). For each strategy, a turbine and an ICU ventilator were used with different FiO(2) settings, with and without leaks. During CPAP, two different HH and NoH were tested. Inspired gases hygrometry was measured, and comfort was assessed. On a bench, we also assessed the impact of ambient air temperature, ventilator temperature and minute ventilation on HH performances (with NIV settings). During NIV, with NoH, gas humidity was very low when an ICU ventilator was used (5 mgH(2)O/l), but equivalent to ambient air hygrometry with a turbine ventilator at minimal FiO(2) (13 mgH(2)O/l). HME and HH had comparable performances (25-30 mgH(2)O/l), but HME's effectiveness was reduced with leaks (15 mgH(2)O/l). HH performances were reduced by elevated ambient air and ventilator output temperatures. During CPAP, dry gases (5 mgH(2)O/l) were less tolerated than humidified gases. Gases humidified at 15 or 30 mgH(2)O/l were equally tolerated. This study provides data on the level of humidity delivered with different humidification strategies during NIV and CPAP. HH and HME provide gas with the highest water content. Comfort data suggest that levels above 15 mgH(2)O/l are well tolerated. In favorable conditions, HH and HMEs are capable of providing such values, even in the presence of leaks.
Article
Full-text available
Heat and moisture exchangers (HMEs) are increasingly used in the ICU for gas conditioning during mechanical ventilation. Independent assessments of the humidification performance of HMEs are scarce. The aim of the present study was thus to assess the humidification performance of a large number of adult HMEs. We assessed 48 devices using a bench test apparatus that simulated real-life physiologic ventilation conditions. Thirty-two devices were described by the manufacturers as HMEs, and 16 were described as antibacterial filters. The test apparatus provided expiratory gases with an absolute humidity (AH) of 35 mg H(2)O/L. The AH of inspired gases was measured after steady state using the psychrometric method. We performed three hygrometric measurements for each device, measured their resistance, and compared our results with the manufacturer data. Of the 32 HMEs tested, only 37.5% performed well (>or= 30 mg H(2)O/L), while 25% performed poorly (< 25 mg H(2)O/L). The mean difference (+/- SD) between our measurements and the manufacturer data was 3.0 +/- 2.7 mg H(2)O/L for devices described as HMEs (maximum, 8.9 mg H(2)O/L) [p = 0.0001], while the mean difference for 36% of the HMEs was > 4 mg H(2)O/L. The mean difference for the antibacterial filters was 0.2 +/- 1.4 mg H(2)O/L. The mean resistance of all the tested devices was 2.17 +/- 0.70 cm H(2)O/L/s. Several HMEs performed poorly and should not be used as HMEs. The values determined by independent assessments may be lower than the manufacturer data. Describing a device as an HME does not guarantee that it provides adequate humidification. The performance of HMEs must be verified by independent assessment.
Article
BACKGROUND: Humidification of inspired gases during mechanical ventilation is essential to maintain structure and function of the respiratory mucosa. Humidity has been most often provided by heated humidifiers. More recently passive humidifiers, (PH) or artificial noses, have been used in selected cases. We evaluated the moisture output of 21 passive humidifiers. DESCRIPTION OF DEVICE: Twenty-one PHs were studied including 11 hygroscopic condenser humidifiers (HCH), 7 hygroscopic condenser humidifier filters (HCHF), and 3 heat and moisture exchanger filters (HMEF). EVALUATION METHODS: All devices were tested for moisture output (mg H2O/L), and resistance (cm H2O · L · s-1) according to International Standard Organization (ISO) 9360. Moisture output was measured by determining weight loss from a water bath during a 2-hour period of ventilation at 3 combinations of frequency (f) and tidal volume (V(T)) (20 breaths/min at 500 mL, 10 breaths/min at 1,000 mL, and 20 breaths/min at 1,000 mL). Dead space was measured by measuring pressure change in the PH during delivery of volume from a calibrated syringe. Resistance was calculated by measuring pressure drop across the PH at a flow of 1 L/s. EVALUATION RESULTS: Moisture output ranged from 19.6 to 33.2 mg H2O/L. As a group, HCHF performed better than HCHs and HMEFs. Dead space ranged from 19 to 94 mL. Resistance ranged from 0.7 to 3.5 cm H2O · L · s-1. CONCLUSIONS: The ISO 9360 system allows ranking of devices in terms of moisture output, dead space, and resistance. These values can all be integrated by the clinician to intelligently choose an appropriate PH. We caution that these results apply specifically to the conditions tested and that results obtained clinically will vary with patient variables, such as temperature and minute ventilation.
Article
We combined a bacteria-filtering heat-moisture exchanger (HMEF), the Pall Conserve (PC), with an unheated Cascade humidifier (UH) to provide the additional humidity necessary to avoid thickening sputum in the long-term mechanically ventilated patient. METHODS AND MATERIALS: We measured the relative humidity and calculated the absolute humidity in the inspired tidal volumes of a healthy, adult patient, with the PC combined and not combined with a UH. Resistance to airflow through the PC was measured continuously for 48 h under two conditions (with and without the UH) and in two positions (upright and horizontal). Clinical testing consisted of ventilating 19 subjects for up to 13 days with the PC-UH combination as the humidifying device. RESULTS: Calculated absolute humidity rose significantly with the PC-UH combination at 5, 15, and 30 min of use. Resistance rose slightly over time, with the greatest increase occurring after 24 h in the horizontally positioned PC combined with the UH. Sputum viscosity changed very little, and in no case was it deemed necessary to provide humidification by heated humidifier. CONCLUSION: We believe that combining the Pall Conserve with an unheated humidifier preserves the advantages of the HMEF and provides the additional humidity required to avoid thickening sputum.
Article
OBJECTIVE:: Previous meta-analyses reported advantages of passive (i.e., heat and moisture exchangers, or HMEs) compared with active (i.e., heated humidifiers, or HHs) humidifiers in reducing the incidence of ventilator-associated pneumonia, but they did not examine the effect of these devices on mortality, length of intensive care unit stay, and duration of mechanical ventilation. In addition, relevant data were recently published. DESIGN:: Meta-analysis of randomized controlled trials comparing HMEs with HHs for the management of mechanically ventilated patients to determine the impact of theses devices on clinical outcomes of such patients. METHODS:: We searched PubMed and the Cochrane Central Register of Controlled Trials as well as reference lists from publications, with no language restrictions. We estimated pooled odds ratios (ORs) and 95% confidence intervals (CIs), using a random effects model. RESULTS:: Thirteen randomized controlled trials, studying 2,580 patients, were included. There was no difference in incidence of ventilator-associated pneumonia among patients managed with HMEs and HHs (OR 0.85, 95% CI 0.62-1.16). There was no difference between the compared groups regarding mortality (OR 0.98, 95% CI 0.80-1.20), length of intensive care unit stay (weighted mean differences, -0.68 days, 95% CI -3.65 to 2.30), duration of mechanical ventilation (weighted mean differences, 0.11 days, 95% CI -0.90 to 1.12), or episodes of airway occlusion (OR 2.26, 95% CI 0.55-9.28). HMEs were cheaper than HHs in each of the randomized controlled trials. CONCLUSION:: The available evidence does not support the preferential performance of either passive or active humidifiers in mechanical ventilation patients in terms of ventilator-associated pneumonia incidence, mortality, or morbidity.
Article
Objective: To determine whether changing heat and moisture exchangers every 48 hrs rather than 24 hrs would affect their efficacy to preserve heat and moisture of expiratory gases. Design: Prospective, controlled, randomized, not blinded, study. Setting: Intensive care unit of a university hospital. Patients: Twenty-nine patients requiring controlled mechanical ventilation and paralysis for >2 days. Interventions: After randomization, the patients were allocated to one of the three following groups: a) group 1, ventilated for 24 hrs with a heat and moisture exchanger; b) group 2, ventilated for 48 hrs with the same heat and moisture exchanger; and c) group 3, ventilated for 48 hrs with a heated humidifier system. Measurements and Main Results: In each patient, during the inspiration phase, the following measurements were performed: a) peak and mean airway pressures; b) mean values of temperature; c) relative and absolute humidity of inspired gases. In each patient, measurements were performed after 24 hrs and after 48 hrs, where appropriate. After 24 hrs, patients in groups 1 and 2 had similar levels of temperature (30.1 +/- 2.7[degree sign]C and 29.2 +/- 2.3[degree sign]C), relative humidity (98.3 +/- 3.6% and 99.3 +/- 3.4%), and absolute humidity (29.1 +/- 2.1 and 29.3 +/- 2.4 mg H2 O/L). Using the same heat and moisture exchanger for 48 hrs rather than 24 hrs did not affect its technical performance. Results showed the following: a) temperature, 24 hrs, 29.2 +/- 2.3[degree sign]C, 48 hrs, 28.7 +/- 1.9[degree sign]C; b) relative humidity, 24 hrs, 99.3 +/- 3.4%, 48 hrs, 99.2 +/- 1.7%; and c) absolute humidity, 24 hrs, 29.3 +/- 2.4 mg H2 O/L, 48 hrs, 28.7 +/- 3.1 mg H2 O/L. Peak and mean airway pressures did not change over the 48-hr study period, with identical tidal and minute volumes in the study patients. Higher levels of temperature and absolute humidity of inspired gases were observed in group 3, compared with groups 1 and 2 (p < .02). Conclusions: Changing the heat and moisture exchanger after 48 hrs rather than 24 hrs did not affect its technical performance in terms of heat and water preservation of ventilatory gases. There is also some indirect evidence of very few, if any, changes in heat and moisture exchanger resistance. However, other large clinical trials should be undertaken to confirm the safety of extending the time between heat and moisture exchanger change. The heated humidifier, supplied with electric energy maintained high levels of humidification and temperature over the 48-hr study period. (Crit Care Med 1998; 26:477-481)
Article
Background: Humidification by artificial means must be provided when the upper airway is bypassed during mechanical ventilation. Heated humidification (HH) and heat and moisture exchangers (HMEs) are the most commonly used types of artificial humidification in this situation. Objectives: To determine whether HHs or HMES are more effective in preventing mortality and other complications in people who are mechanically ventilated. Search strategy: We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2010, Issue 4) and MEDLINE, EMBASE and CINAHL (January, 2010) to identify relevant randomized controlled trials. Selection criteria: We included randomized controlled trials comparing HMEs to HHs in mechanically ventilated adults and children. We included randomized crossover studies. Data collection and analysis: We assessed the quality of each study and extracted the relevant data. Where appropriate, results from relevant studies were meta-analyzed for individual outcomes. Main results: We included 33 trials with 2833 participants; 25 studies were parallel group design (n = 2710) and 8 crossover design (n = 123). Only 3 included studies reported data for infants or children. There was no overall effect on artificial airway occlusion, mortality, pneumonia, or respiratory complications; however, the PaCO(2) and minute ventilation were increased when HMEs were compared to HHs and body temperature was lower. The cost of HMEs was lower in all studies that reported this outcome. There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia and that blockages of artificial airways may be increased with the use of HMEs in certain subgroups of patients. Authors' conclusions: There is little evidence of an overall difference between HMEs and HHs. However, hydrophobic HMEs may reduce the risk of pneumonia and the use of an HMEs may increase artificial airway occlusion in certain subgroups of patients. Therefore, HMEs may not be suitable for patients with limited respiratory reserve or prone to airway blockage. Further research is needed relating to hydrophobic versus hygroscopic HMEs and the use of HMEs in the pediatric and neonatal populations. As the design of HMEs evolves, evaluation of new generation HMEs will also need to be undertaken.