2. OBJECTIVE
•Describe how airway heat and moisture exchange
normally occurs.
•State the effect dry gases have on the respiratory
tract.
•State when to humidify and warm inspired gas.
•Describe how various types of humidifiers work.
•Identify the indications, contraindications, and
hazards that pertain to humidification during
mechanical ventilation.
•Describe how to monitor patients receiving
humidity therapy.
•Describe how to identify and resolve common
problems with humidification systems.
3. HUMIDITY THERAPY
•Humidity is the quantity of moisture in
air or gas that is caused by the addition
of water in a gaseous state, or vapor.
Also called molecular water or invisible
moisture.
•Clinical Uses of Humidity
• To provide 100% body humidity of the
inspired gas for patients with ET tubes or
tracheostomy tubes
• To humidify dry therapeutic gases
4. NORMAL AIRWAY HUMIDIFICATION
• The nose warms, humidifies, and filters inspired
air.
• The pharynx, trachea, and bronchial tree also
warm, humidify, and filter inspired air.
• By the time the inspired air reaches the
oropharynx, it has been warmed to approximately
34°C and is 80% to 90% saturated with H2O.
• By the time the inspired air reaches the carina, it
has been warmed to body temperature (37°C) and
is 100% saturated.
• when the inspired air is fully saturated (100%) at
37°C, it holds 44 mg H2O per liter of gas and
exerts a water vapor pressure of 47 mmHg.
• As inspired gas moves into the lungs, it achieves
BTPS conditions (body temperature, 37°C;
barometric pressure; saturated with water
5.
6. ABSOLUTE AND RELATIVE HUMIDITY
1. Absolute humidity is the amount of water in
a given volume of gas; its measurement is
expressed in milligrams per liter.
2. Relative humidity is a ratio between the
amount of water in a given volume of gas
and the maximum amount it is capable of
holding at that temperature (capacity). Its
measurement is expressed as a percentage
and is obtained with a hygrometer.
3. Relative humidity= absolute humidity
capacityx100
7. ISOTHERMIC SATURATION
BOUNDARY(ISB)
As inspired gas moves into the lungs, it achieves
BTPS conditions (body temperature, 37°C;
barometric pressure; saturated with water
vapor[100% relative humidity at 37°C]). This point,
normally approximately 5cm below the carina, is
called the isothermic saturation boundary(ISB).
Above the ISB, temperature and humidity decrease
during inspiration and increase during exhalation.
Below the ISB, temperature and relative humidity
remain constant (BTPS).
Numerous factors can shift the ISB deeper into the
lungs.
8. The ISB shifts distally when a person breathes through the
mouth rather than the nose; when the person breaths cold,
dry air; when the upper airway is bypassed (breathing
through an artificial tracheal airway); or when the minute
ventilation is higher than normal.
When this shift of ISB occurs, additional surfaces of the
airway are recruited to meet the heat and humidity
requirements of the lung.
This recruitment of airways that do not typically provide
this level of heat and humidity can have a negative impact
on epithelial integrity.
These shifts of the ISB can compromise the body’s normal
heat and moisture exchange mechanisms, and humidity
therapy is indicated.
9. TYPES OF HUMIDIFIERS
Humidifiers are either active (actively adding heat or
water or both to the device-patient interface) or passive
(recycling exhaled heat and humidity from the patient).
Active humidifiers typically include
1. Bubble humidifiers
2. Passover humidifers
3. Nebulizers of bland aerosols, and
4. Vapourizers
Passive humidifiers refer to typical heat and moisture
exchangers (HMEs).
10. INDICATION
Primary
Humidifying dry medical gases
Overcoming humidity deficit created when upper
airway is bypassed
Secondary
Managing hypothermia
Treating bronchospasm caused by cold air
11. CLINICAL SIGNS AND
SYMPTOMS OF INADEQUATE
AIRWAY HUMIDIFICATION
Atelectasis
Dry, nonproductive cough
Increased airway resistance
Increased incidence of infection
Increased work of breathing
Patient complaint of substernal pain and airway dryness
Thick, dehydrated secretions
14. HUMIDIFIER PERFORMANCE
Temperature: as temperature increases,
capacity (potential humidity) will increase
Surface area: the greater the surface area, the
more potential for evaporation
Contact time: the longer the time of contact, the
more time for evaporation to occur
Thermal mass: the more water in the humidifier,
the more potential for transfer of heat
16. BUBBLE HUMIDIFIER
Gas passes through tube to bottom of water
reservoir
Gas bubbles through reservoir
Unheated bubbles through humidifier
Provides humidity for oxygen therapy
20. HEATED HUMIDIFIER
Adding heat increases absolute humidity of gas
Heating of gas increases risk of condensation in
tubing, causing obstruction
Risk is decreased by using large-bore tubing
Heated wire circuits are used to decrease
amount of condensation in circuit
21. HEAT MOISTURE EXCHANGER
Considered to be passive humidifier
Traps heat and humidity in expired gas
Has been used to provide humidity for
spontaneously and mechanically ventilated
patients
Types of heat moisture exchangers (HMEs):
Simple condenser
Hygroscopic condenser
Hydrophobic condenser
22. Simple condenser
humidifier
Contains condenser
element to trap heat and
humidity of expired gas
Retains about 50% of
expired heat and humidity
Maximum absolute
humidity is 18 to 28 mg/L
Hygroscopic heat
exchanger
Uses condenser element
made of paper, wool,
or foam
Material includes a salt
Maximum absolute
humidity is 22 to 34 mg/L
23. Active Heat Moisture
Exchangers
Add heat or humidity (or
both) to inspired gas
External heat and
moisture is introduced into
inspired gas
Capable of providing
100% relative humidity at
BTPS
24. CONTRAINDICATIONS
There are no contraindication to providing physiologic
conditioning of inspired gas during mechanical ventilation.
However, an HME is contraindicated in the following
circumstances
For patients with thick, copious, or bloody secretions
For patients with an expired tidal volume less than 70% of
the delivered tidal volume (eg., patients with large
bronchopleural fistulas or incompetent or absent
endotracheal tube cuffs)
For patients whose body temperature is less than 32°C
For patients with high spontaneous minute volumes (>10
L/min)
For patients receiving in-line aerosol drug treatments (an
HME must be removed from the patient circuit during
treatments)
25. HAZARDS AND
COMPLICATIONS
Hazards and complication associated with the use of
heated humidifier (HH) and HME devices during
mechanical ventilation include the following:
1. High flow rates during disconnect may aerosolize
contaminated condensate in heated humidifer circuit
2. Increased work of breathing (HME or HH)
3. Elevated airway pressures caused by condensation
(HH)
4. Inadvertent overfilling resulting in unintended tracheal
lavage (HH)
5. Inadvertent tracheal lavage from pooled condensate in
circuit (HH)
26. MONITORING
The humidifier should be inspected during the patient-ventilator
system check, and condensate should be inspected and replaced if
secretions have contaminated the insert or filter.
The following should be recorded during equipment inspection:
1. During routine use on an intubated patient, an HH should be set to
deliver inspired gas at 33°C ± 2°C and should provide a minimum of
30 mg/L of water vapor.
2. Inspired gas temperature should be monitored at or near the patient’s
airway opening (HH)
3. Specific temperature may vary with the patient’s condition; airway
temperature should never exceed 37°C.
4. For heated wire circuits used with infants, the probe must be placed
outside the incubator or away from the radiant warmer.
5. The high temperature alarm should be set no higher than 37°C, and
the low setting should not be less than 30°C.
6. Water level and function of automatic feed system (if applicable)
should be monitored.
27. PROBLEM SOLVING AND
TROUBLESHOOTING
Common problems with humidification systems
include dealing with condensation, avoiding cross
contamination, and ensuring proper conditioning of
the inspired gas.
Condensation
As the gas cools, its water vapor capacity
decreases, resulting in condensation. Factors
influencing the amount of condensation include
1. The temperature difference across the system
(humidifier to airway)
2. The ambient temperature
3. The gas flow
4. The set airway temperature; and
28. Condensation can disrupt or occlude gas flow through the circuit,
potentially altering fractional inspired oxygen or ventilator function or
both.
Condensate can work its way toward the patient and be aspirated. For
these reasons, circuits must be positioned to drain condensate away
from the patient and must be checked often, and excess condensate
must be drained from heated humidifier breathing circuits on a regular
basis.
Several techniques are used to minimize problems with breathing circuit
condensate. One common method is to place water traps at low points
in the circuit(both the inspiratory and the expiratory limbs of ventilator
circuits).
29. CROSS CONTAMINATION
Aerosols and condensate from ventilator circuits
are known sources of bacterial colonization.
However, advances in both circuit and humidifier
technology have reduced the risk of nosocomial
infection when these systems are used.
Heated wire circuits reduce production and
pooling of condensate within the circuit.
In addition, the high reservoir temperature in
humidifiers are bactericidal.
30. IMPORTANT POINTS CONCERNING
HUMIDIFIERS
1. Most nonheated humidifiers have a pressure pop-off valve set at 2
psi, after the device is set up, the tubing of the oxygen delivery
device (e.g., cannula, mask ) should be kinked to obstruct flow. If the
pop-off sounds, there are no leaks. If no sound is heard, all
connections, as well as the humidifier top, should be tightened.
2. Water levels of all humidifiers should be maintained at the levels
marked on the humidifier jar to ensure maximum humidity output.
3. Condensation occurs in the tubing of heated humidifiers. This water
should be discarded in a trash container or basin and should never
be put back into the humidifier.
4. Warm moist areas, such as heated humidifiers, are a breeding
ground for microorganisms (especially pseudomonas species). The
humidifier should be replaced every 24 hours(2).
5. Without a heated wire circuit, the humidifier may need to be heated
to as much as 50°C for the gas temperature to approximate body
temperature (37°C) by the time it reaches the patient’s upper airway.
As the highly saturated and warm gas passes through the ventilator
circuit, ambient air surrounding the circuit tubing cools(3).
31. REFERENCES
EGANS, Fundamentals of Respiratory Care.
Respiratory care exam review, Gary Persing
Clinical Application of Mechanical ventilation Susan
Pilbeam’s.
