Presentor : Dr. kailash mittal
Moderator : Dr. M LTak sir
Dr. Neelam mam
HUMIDIFIER AND SCAVENGING
Humidification is a method to artificially condition the gas used
in respiration of a patient as a therapeutic modality.
Active method is by adding heat or water or both to the device &
passive which is recycling heat and humidity which is exhaled by
Indications of Humidification
Overcoming humidity deficit created when upper
airway is bypassed
To humidify dry medical gases
To manage hypothermia
To treat bronchospasm caused by cold air
Clinical signs and symptoms of
Dry and non-productive cough
Increased airway resistance
Increased work of breathing
Increased incidence of infection
Thick and dehydrated secretions
Complaints of substernal pain and airway dryness
Heat and moisture exchange is a primary function of the
upper respiratory tract, mainly the nose.
The nasal mucosal lining is kept moist by secretions from
mucous glands, goblet cells, transudation of fluid through
cell walls, and condensation of exhaled humidity.
As the inspired air enters the nose, it warms (convection) and
picks up water vapour from the moist mucosal lining
Condensation occurs on the mucosal surfaces during
exhalation, and water is reabsorbed by the mucus .
The mouth is less effective at heat and moisture exchange
than the nose because of the low ratio of gas volume to moist
and warm surface area and the less vascular squamous
epithelium lining of oropharynx and hypopharynx.
As inspired gas moves into the lungs, it achieves BTPS conditions
(body temperature, 37° C; barometric pressure; saturated with
water vapor [100% relative humidity )
This point, normally approximately 5 cm 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
The ISB shifts distally :- when a person breathes through the
mouth rather than the nose; when the person breathes 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
These shifts of the ISB can compromise the body’s normal heat
and moisture exchange mechanisms, and humidity therapy is
Principles of humidifier
Temperature – As the temperature of a gas increases, its ability
to hold water vapour (capacity) increases .
Surface area – There is more opportunity for evaporation to
occur with greater surface area of contact between water and gas.
Time of contact – There is greater opportunity for evaporation
to occur, when a gas remains in contact with water for longer
Method of humidification
a. Passive (Heat and Moisturea. Passive (Heat and Moisture
Exchangers/ HMEs) – hydrophobic/Exchangers/ HMEs) – hydrophobic/
b. Active – unheated/ heatedb. Active – unheated/ heated
Simplest designs are Heat and Moisture Exchangers
Also called as condenser humidifier, artificial nose,
Swedish nose, nose humidifier, regenerative humidifier,
Disposable devices that trap some exhaled water and
heat, and deliver them to patient on subsequent
inhalation (minimize water and heat loss)
When combined with a filter for bacteria and viruses
called Heat and Moisture Exchanging Filter (HMEF)
particularly important when ventilating patients with
respiratory infections or compromised immune system
Exchanging medium enclosed
in plastic housing
Vary in size, shape, dead
space, pediatric and neonatal
HMEs with low dead space
May have a port to attach
gas sampling line for
respiratory gas monitor
Placed between ET tube and
Hydrophobic HMEs –
1.1. Hydrophobic membrane with smallHydrophobic membrane with small
pores, pleated to increase surfacepores, pleated to increase surface
2.2. Allow passage of water vapour but notAllow passage of water vapour but not
liquid water at usual ventilatoryliquid water at usual ventilatory
3.3. Efficient bacterial and viral filtersEfficient bacterial and viral filters
4.4. Performance may be impaired by highPerformance may be impaired by high
ambient temperaturesambient temperatures
Contain low thermal conductivity wool ,foam or paper like material
coated with lithium chloride or calcium – to recollect the moisture
In exhaletion: some vapour will condense and the rest will absorbed by
Inspiration: the low water pressure in the inspired air cause released the water
molecule direct from hygroscopic salt
high efficiency compare to hydrophobic HMEs
approximately 70% efficiency that is 40 mg/l on exhaled, 27 mg/L on return
TypeType HygroscopicHygroscopic HydrophobicHydrophobic
Heat and moistureHeat and moisture
exchanging efficiencyexchanging efficiency
Effect of increased tidalEffect of increased tidal
volume on HMEvolume on HME
Slight decreaseSlight decrease Significant decreaseSignificant decrease
Filtration efficiencyFiltration efficiency
when drywhen dry
Filtration efficiencyFiltration efficiency
when wetwhen wet
Resistance when wetResistance when wet SignificantlySignificantly
Slightly increasedSlightly increased
Effect of nebulisedEffect of nebulised
Greatly increasedGreatly increased
Little effectLittle effect
ideal HME should operate at 70% efficiency or better providing at least
30 mg/L water vapour.
easy to use
Small and lightweight
silent in operations
do not required water, temperature monitor, alarms
No burns, no danger of over hydrations and electric shock.
less effective than active humidifiers
can deliver only limited humidity
increased in dead space (Boots et al 2006)
Need change the HME every 24(Boots et al 1993) or 48(Djedaini et al
For patients with thick, copious, or bloody secretions
For patients with an expired tidal volume less than 70%
of the delivered tidal volume (e.g., 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
Add water to gas by passing the gas over a water
chamber (passover humidifier) or through a
saturated wick (wick humidifier), bubbling it
through water (bubble-through humidifier), or
mixing it with vaporized water (vapour-phase
Unlike passive humidifiers, they do not filter
2 types –
bubble-through devices used to increase humidity
in oxygen supplied to patients via facemask or
Simple containers containing distilled water through
which oxygen is passed and it gets humidified
Maximum humidity that can be achieved is 9mg
Incorporate a device to warm water in the
humidifier, some also heat inspiratory tube
Humidification chamber – transparent (easy to
check water level) contains liquid water,
Heat source – heated rods immersed in water or
plate at bottom of humidification chamber
Inspiratory tube – conveys humidified gas from
humidifier outlet to patient
If unheated gas will cool and lose some of its
moisture as it travels to the patient, water trap necessary to
collect condensed water
Heated or insulated more precise control of
temperature and humidity delivered to patient, avoids
Temperature monitor – to measure gasto measure gas
temperature at patient end of breathing systemtemperature at patient end of breathing system
1.1.Servo-controlled unitsServo-controlled units – automatically regulates– automatically regulates
power to heating element in response topower to heating element in response to
temperature sensed by a probe near patienttemperature sensed by a probe near patient
connection/ humidifier outlet, these deviceconnection/ humidifier outlet, these device
equipped with alarmequipped with alarm
2.2.Nonservo-controlled unitsNonservo-controlled units – provides power to– provides power to
heating element according to setting of a control,heating element according to setting of a control,
irrespective of delivered temperatureirrespective of delivered temperature
Controls – most humidifier allow temperature selection at end ofmost humidifier allow temperature selection at end of
delivery tube or at humidification chamber outletdelivery tube or at humidification chamber outlet
AlarmsAlarms alarm may warn when temp. at patient end of the circuitalarm may warn when temp. at patient end of the circuit
deviates from set temp , when displacement of temperature probe,deviates from set temp , when displacement of temperature probe,
disconnection of heater wire, low water level in humidificationdisconnection of heater wire, low water level in humidification
chamber, faulty airway temperature probe , lack of gas flow in thechamber, faulty airway temperature probe , lack of gas flow in the
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
Humidifier must be lower than patient to avoid risk
of water running down the tubing into the patient
Condensate must be drained periodically & a water
trap inserted in the most dependent part of the
tubing to prevent blockage or aspiration
Heater wire in delivery tube should not be bunched,
but strung evenly along length of tube
Delivery tube should not rest on other surfaces or
be covered with sheets, blankets, or other
materials; a boom arm or tube tree may be used
1.Capable of delivering saturated gas at body
temperature or above, even with high flow rates
2.More effective humidification than an HME
1.Bulky and somewhat complex
2.Involve high maintenance costs, electrical hazards,
and increased work (temperature control, refilling
the reservoir, draining condensate, cleaning, and
3.Offers relatively little protection against heat loss
during anesthesia as compared to circulating water
and forced-air warming
Assessment of need
Either an HME or an HH can be used to condition inspired
HMEs are better suited for short-term use (≤96 hours) and
HHs should be used for patients requiring long-term
mechanical ventilation (>96 hours) or for patients for whom
HME use is contraindicated.
Produces and disperses liquid particles in a gas stream or
Use - produce humidification & deliver drug such as
bronchodilator, mucolytic agent and decongestant
Size of the water droplet is between 0.5 to 5µm
Particles more than 5µm unable to reach the peripheral
Particles less 0.5µm is very light, and will come back with
expired gases without being deposited in airways
2 types of nebulizer
Works: by forced a jet of high-pressure
gas into a liquid - inducing shearing
forces - breaking the water up into fine
produces particles of size 5 to 30 µm
only 30 to 40% of particles produced
are in optimal range
Most of the particles get deposited in
wall of main airways
used piezoeeletric crystal
Crystal transducer converts: radio waves
into high-frequency mechanical
vibration is transmitted to the water
The high mechanical energy creates
cavitation in the fluid
it formed a standing wave which will
disperses liquid particles
Frequency of oscillation determines the
size of the water particles
Aerosol size of 1 to 10 µm
95% of particles produced are in optimal range
Particles deposited directly in airway
Very effective for deliver bronchodilator
Hazards from nebulizer:
cause over hydrations
Infection can be transmitted
edema of the airway wall
Advantages and disadvantages
It can carry air that fully saturated with water vapor without
We can increase the amount of the water vapor in the inhaled
The pneumatic nebulizer needs high air flow to operate.
The ultrasonic nebulizer need electric supply to operate thus it
may cause electric shock
scavenging is the collection and subsequent removal of waste
anesthetic gases from both the anesthesia machine and the
Trace level of an anesthetic gas is a conc. far below that
needed for clinical anesthesia or can be detected by smell
Trace gases conc. depending on FGF, ventilation system , the
length of time of anesthesia, anesthetic technique and other
Trace gas level expressed in parts per million (ppm)
Problems attributed to trace gases
Spontaneous abortions :
Higher rates of spontaneous abortion in OR personnel than
in women in other settings.
Infertility : Studies found higher than expected rates of
involuntary infertility among exposed
Impaired Skilled performance : one study showed that
neuropsychological symptoms and tiredness were reported
more by individuals in OR that are less scavenged
Birth Defects : Studies in human found increase in congenital
abnormalities in children of exposed personnel
Carcinogenicity : A large study found higher risk of cancer in
females than males who are exposed, but data has been
Liver disease : recurrent hepatitis – halothane reported in
Hematological : higher rate of leukamia.
Cardiac Disease : higher Freq of HTN and
In 1977 National Institute for
Occupational Safety and Health
recommended exposure limits for
trace gas level (nitrous oxide and
halogenated agent )
0.5 + 25
The 2 major causes of waste gas contamination in the
Equipment failure or lack of understanding of proper
The anesthetic technique used -
Failure to turn off gas flow control valve and vaporizers when
the circuit is disconnected from the patient.
use poorly fitting masks.
Flushing of circuit in room.
Using uncuffed endotracheal tubes that do not create a
completely sealed airway or using cuffed tubes without
inflating the cuff
Spilling liquid anesthetic during the filling of vaporizers.
Use of breathing circuits other than circle system
The use of scavenging devices with anesthesia delivery systems
is the most effective way to decrease waste anesthetic gases.
An efficient scavenging system is capable of reducing ambient
concentrations of waste gases by up to 90%.
1.Gas collecting assembly
Captures excess anesthetic gases and delivers it to the transfer
WAG are vented from anesthesia system through either
adjustable pressure limiting valve or ventilator relief valve.
Conventional machine have seprate outlet port for these valve
however newer have only one
some anesthetic workstations may also exhaust the ventilator
drive gas in to scavenging system
The transfer tubes carries excess gas from gas collecting assembly to
The tubes must have 30 mm connectors on either end, sometimes yellow
The tubes should be sufficiently rigid to prevent kinking and as short as
possible to minimize the chance of occlusion.
Separate tubes from the APL valve and ventilator relief valve merge into a
single hose before they enter scavenging interface.
If the transfer tube is occluded, baseline breathing circuit pressure will
increase and barotrauma can occur.
The scavenger interface is the most important component because it
protects the breathing circuit or ventilator from excess positive or
the interface should limit pressure between -.5 and 3.5 cm of h2o under
normal working condition.
Positive-pressure relief is mandatory, irrespective of the type of disposable
system (active or passive) used, to vent excess gas in case of occlusion
distal to interface.
negative pressure relief will be necessary in active disposable system to
protect breathing circuit or ventilator from subatmospheric pressure .
scavenger interfaces may be open
It contains no valves and is open to
the atmosphere, allowing positive
and negative pressure relief.
Open interfaces should be used
only with active disposable systems
that have a central evacuation
open interfaces require a
reservoir because waste gases are
intermittently discharged in surges
whereas flow from the evacuation
system is continuous.
The efficiency of it depends on several factors:
A.The vacuum flow rate per min must equal or exceed the
minute volume of excess gases to prevent spillage.
B.Spillage will occur if the volume of a single exhaled
breath exceeds the capacity of reservoir.
are safer for the patients.
It communicates with the atmosphere through valves.
Two types of closed interfaces are commercially available:
positive pressure relief only
positive and negative pressure relief
POSITIVE PRESSURE RELIEF ONLY:
It has a single positive pressure relief valve and is designated to be used
only with passive disposable systems.
Transfer of the waste gas from the interface to the disposable system
relies on the slight positive pressure of the waste gases leaving the patient’s
breathing system, because a negative pressure evacuation system is not
In this system reservoir bag is not required.
POSITIVE AND NEGATIVE PRESSURE RELIEF:
It has positive and negative pressure relief valve in addition to a reservoir
It is used with active disposable systems.
The effectiveness of a closed system in preventing spillage depends on:
the rate of waste gas inflow
the evacuation flow rate
the size of the reservoir
Leakage occurs only when the reservoir bag becomes fully inflated and
pressure increases sufficiently to open the positive pressure relief valve .
4.Gas disposal tubing
The gas disposable tubing conducts waste gas from the Scavenging
interface to the gas disposable assembly.
It should be collapse proof and should run overhead, if possible to
minimize the chance of accidental occlusion.
Connection to an active gas disposable system should be DISS type
5.Gas disposal assembly
It ultimately eliminates excess waste gas.
It is of two types:
most commonly used. It uses central evacuation system.
A vacuum pump serves as mechanical flow inducing device that removes
the waste gases.
An interface with a negative pressure relief valve is mandatory because
the pressure within the system is negative.
Central evacuations are
- Piped Vacuum - central vaccum system
- Active duct system - employs flow inducing devices (fans ,
pumps , blowers etc..) to move large volume of gas at low
Convenient in large hospitals, where many machines are in use in
More effective at keeping pollution low level because most leaks will
Vacuum system and pipe work is a major expense
not a automatic must be turn ON and OFF
Passive disposable system:
does not use a mechanical flow inducing device.
anesthetic gases flow through the system by the pressure raised
above atmospheric by the patient exhaling, by manually
squeezing the reservoir beg , or by ventilator
Positive pressure relief is mandatory, but a negative pressure
relief and reservoir are not.
- Room ventilation system
- Recirculating or nonrecirculating
- Piping direct to atmosphere
- Adsorption devices
- Catalyst decomposition
use activated charcoal or zeolite
connected to the outlet of the
removes halogenated anesthetics but
not nitrous oxide
These are simple and portable
Halogenated gases not release to
atmosphere (decrease green house
They are fairly expensive and are effective for short period of
replaced regularly and pose to storage and disposal
Does not remove nitrous oxid
Catalytic Decomposition :
Catalytic decomposition can be used to convert nitrous oxide
to nitrogen and oxygen, reducing its contribution to the
Evaluation of Anesthetic Equipment
Each piece of equipment involved in the delivery of inhalant
anesthetics should be evaluated regularly to assure its function and
Procedures for checkout of anesthesia equipment, depending
on the equipment to be used, should include the following:
Status of the high-pressure system, including the oxygen
supply and nitrous oxide supply - The nitrous oxide supply
should not leak when the cylinder valve is on and the nitrous oxide
flowmeter is off.
Status of the low-pressure system (flowmeter function) - A
negative-pressure leak test should be performed at the common gas
outlet or the outlet of the vaporizer immediately upstream from the
Status of the breathing system - An appropriate leak test for a
circle system and Noncircle systems should be done. The quantity
of leakage can be measured by determining the flow rate of oxygen
necessary to maintain a constant pressure in the system, and the
leak rate should be less than 300 ml/min at 30 cm of h2O.
Status of the scavenging system - The scavenging system should
be properly attached at all connectors, and the appropriate vacuum
should be assured for active systems. If charcoal canisters are
employed for scavenging, they should be changed at appropriate
Monitoring of the Effectiveness of
Monitoring trace-gas concentrations in the workplace provides a
quantitative assessment of the effectiveness of a waste-gas control
An air-monitoring program is most appropriately started after anesthesia
delivery systems have been equipped with scavenging systems and after
other techniques for minimizing waste gas pollution are in place.
An ideal approach would include frequent air monitoring, at least
Equipment for determining trace gas conc.
infrared analyzer , dosimeter . Ionizing leak detector
Unscavenged operating rooms show 10-70 ppm halothane, and
400-3000 ppm N2O.
scavenging brings these levels down to 1 and 60 ppm
Adding careful attention to leaks and technique can yield levels
as low as 0.005 and 1 ppm.
Scavenging system functionally extends the anesthesia circuit all the way
from the anesthesia machine to the disposable site.
Obstruction of scavenging pathway can cause excessive positive pressure in
the breathing circuit and barotrauma can occur.
excessive vacuum applied can result in undesirable negative pressures
within breathing system.
Loss of Monitoring Input – it may mask the strong odor of a volatile
anesthetic agent, delaying recognition of an overdose
Alarm failure – neg. pressure from the scavenging system interface prevent
the bellows from collapsing when breathing system is disconnected & Low
airway pressure alarm not activated.