Humidification
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu),
Dip. Diab. DCA, Dip. Software statistics
PhD (physio)
Mahatma Gandhi medical college and
research institute , puducherry – India
Definition
• Humidity is a measure of the amount of
water vapour in a gas.
• Absolute humidity is defined as actual mass of
water vapour present in a known volume of
gas.
• 34 mg / l to 45 mg / l
• Upper airway to alveolus
Relative humidity
• Relative humidity is defined as the ratio of
• the mass of water vapour in a given volume of
gas to the maximum amount of water vapour
that the same gas can hold at the same
temperature.
• Relative humidity is expressed as
a percentage.
Yes - humidification
• humidification maintains mucosal integrity, ciliary
activity, prevents the drying of secretions and helps
in easy expulsion of respiratory secretions when
coughing.
No
• (e.g. ventilating a patient with dry gas through a
tracheal or tracheostomy tube) can result in cracking
of mucosa, drying of secretions, keratinisation of the
tracheo-bronchial tree, reduction in ciliary activity,
atelectasis and infection
Clinical signs
•
•
•
•
Dry nonproductive cough
Dyspnoea
Substernal pain
Thick secretions
Over-humidification
It can result in water intoxication, especially in
neonates and infants in intensive care, water
clogging and airway burns
Normal airway humidification
• While nose breathing at rest, inspired gases
become heated to 36°C and are about 80% to
90% saturated with water vapour.
• Mouth breathing reduces this to 60% to 70%
Aims of humidity therapy
• Gas at nose/mouth
• 50% RH with 10 mg/litre --- 22 deg.
• Gas at hypopharynx
• 95 % RH with 34 mg/l --- 29 degree
• Mid trachea
• 100 % with 40 mg/l. 31 – 35 deg.
Sources
• CO2 absorbent
• Exhaled gases
• Rinsing the tubes
Measure humidity
• Hair hygrometer
This is based on the principle that the length of hair
increases with increasing humidity It is fairly
accurate between 30 and 90%.
• Wet and dry bulb hygrometer
Two mercury thermometers, one in ambient
temperature and the other in contact with water
through a wick are used. Rate of evaporation prop.
Humidity
Measure humidity
• Regnault’s hygrometer
• Mass spectrometer
• principle of reduction in the ultraviolet light
transmitted through the medium containing
water vapour
Types of humidifiers
•
•
•
•
Low flow
Less than the inspiratory needs
Bubble
Simple diffuser
• High flow
Inspiratory needs are met
HME , wick type
Bubble humidifier
Bubble diffuser humidifiers
Picture of bubble- diffuser
Function
•
•
•
•
Gas comes from DISS
Capillary tube
Exits as small bubbles
Pick up water vapour and come out
• Diffuser – smaller bubbles, greater surface
area and better humidification
Factors
• Flow of gas
• Water level
• Ambient temperature
• 5 l/ min- AH is 10 - 20 mg/l, RH is 40 % at 37
deg.
Disadvantages
• Transport water borne microbes
• High gas flows an aerosol is created and
microbes can be transferred
• High flows --- delivery tube kinked – high
pressure develops – PRV( pressure relief valve)
– alarm at 2 PSI can be set.
High flow humidifiers
• HME
• Heat moisture exchangers
• Disposable devices that trap some exhaled water
and
heat,
and
deliver
them
to
patient
on
subsequent inhalation (minimize water and heat
loss)
• combined with a filter for bacteria and viruses 
Heat and Moisture Exchanging Filter (HMEF)
Swedish nose
First – aluminium
• Most modern HMEs are of 2 types:
a. Hydrophobic (not much used)
b. Hygroscopic
Hydrophobic HMEs –
1. Hydrophobic membrane with small pores,
pleated to increase surface area
2. Allow passage of water vapor but not liquid
water at usual ventilatory pressures
3. Efficient bacterial and viral filters
4. Performance may be impaired by high
ambient temperatures
Hygroscopic HMEs –
1. Wool, foam or paper like material coated
with moisture-retaining chemicals
2. Medium may be impregnated with a
bactericide
• When wet – performance is poor
Minimum standard
• Its not 20 – 20 cricket
• Its 30 – 30 cricket
• Minimum 30 mg/ litre at 30 deg. c
Advantages
1.
2.
3.
4.
5.
Inexpensive
Easy to use
Small, lightweight, simple in design
Silent in operation
Do not require water/ external energy
source/ temperature monitor/ alarms
6. No danger of overhydration/
hyperthermia/ burns/ electrical shock
Disadvantages
1. Can deliver only limited humidity
2. Insignificant
contribution
to
temperature
preservation
3. Less effective than active humidifiers, specially
after intubation lasting for several days
4. Increased dead space  may necessitate
increase in tidal volume  increased work of
breathing
If you are in continuous search of an
ideal one ???
Can We use HME here ??
• Preexisting pulmonary disease with copious
secretions
• Bloody secretions
• Expired tidal volume is less than 70 % of the
delivered tidal volume ( if there is no other
problem)
•
Be cautious
Heated humidifier
HEATED HUMIDIFIERS
• Incorporate a device to warm water in
the humidifier, some also heat
inspiratory tube
• Humidification chamber
• Heat source
• Temperature monitor
• Thermostat
• Controls
• Alarms
Use
• In circle system, heated humidifier is placed
in the inspiratory limb downstream of
unidirectional valve by using an accessory
breathing tube
• Must not be placed in the expiratory limb
• Filter, if used, must be placed upstream of
humidifier to prevent it from becoming
clogged
• In Mapleson systems, humidifier is usually
placed in fresh gas supply tube
Clinical tips
• Humidifier must be lower than patient
• Condensate must be drained periodically
• Delivery tube should not rest on other
surfaces or be covered with sheets
• Beware alarms are set for temperature –
not for humidity
Advantages
1. Capable of delivering saturated gas
at body temperature or above, even
with high flow rates
2. More effective humidification than
an HME
Disadvantages
• Water spillage into the breathing circuit and
even into tracheobronchial tree. A water trap
will help reduce this problem.
• Airway burns due to thermostat failure and
overheating.
• Colonization of water with harmful bacteria
can occur. This may be reduced by heating the
water to 60°C.
How was the progress
• Hot water bath –(upto 50 deg)-- water
condensate because there was difference in
temperature between the humidifier and the
patient end.
• Then a heated wire was introduced in the
inspiratory system – then also in the expiratory
tubes.
• The flow transducers in the ventilators confused
with water vapour to confuse readings and hence
at the expiration there was a heating element to
get the gas to 37. deg
Types of humidifiers
•
•
•
•
Low flow
Less than the inspiratory needs
Bubble
Simple diffuser
• High flow
Inspiratory needs are met
HME , vapor phase , wick type
One more classification
• Passive
• HME
• Active -they do not filter respiratory
gases
• Heated and unheated
• Nebulizers
Wick on the sides of the bottle
WICK
Aerosol therapy – different topic
MUCOLYTICS
• Agents capable of dissolving,
digesting or liquefying mucus
•
•
•
•
N-acetylcysteine (NAC)
Mesna
Sodium bicarbonate
Dornase alpha (Pulmozyme)
Act by
1. Weakening of intermolecular forces
binding adjacent glycoprotein chains
– Disruption of Disulfide Bonds (NAC, Mesna)
2. Alteration of pH to weaken sugar side
chains of glycoproteins (Soda bicarb.)
3. Destruction of protein (Proteolysis)
contained in the glycoprotein core
– Breaking down of DNA in mucus (Dornase
alpha
N-acetylcysteine (NAC)
• Sulfhydryl - containing tripeptide
• Better known as the antidote for
acetaminophen overdose
• Primarily a mucolytic agent that acts by
disrupting the disulfide bridges between
mucoprotein strands in sputum
NAC
NAC (contd.)
• liquid preparation (10 or 20% solution) that can be
given as an aerosol spray, or injected directly into the
airways
• Aerosolized NAC -- avoided when possible provoke
coughing and bronchospasm
• Direct instillation of NAC into the tracheal tube is
preferred, especially when there is an obstruction
• Daily use of NAC is not advised because the drug
solution is hypertonic (even with the saline additive)
and can provoke bronchorrhea
Summary
•
•
•
•
•
•
Humidity – definition , types
Normal – physiological –
Indications
Types two classifications
HME and F
Bubble , diffuser , heated , nebulizers
Thank you all