Presented By Dr. Mohamed Sayed Shorbagy
Lecturer of Anesthesia and Intensive care Faculty of Medicine
Ain-Shams University2012
http://telemed.shams.edu.eg/moodle
Presented By Dr. Mohamed Sayed Shorbagy
Lecturer of Anesthesia and Intensive care Faculty of Medicine
Ain-Shams University2012
http://telemed.shams.edu.eg/moodle
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Humidity= safety?Importance of humidity of inspired gases: Humidity and warming of inspired air occurs by
nose and upper respiratory tract. By-
passing the nose
Dry inspired gases
↑ viscosit
y (mucus plug)
+Ciliary dysfunction
+hypothermia
Why to
care ?
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Particularly in
Mechanically ventilated
I.C.U patient
Prolonged anesthesia in pediatrics &
geriatrics
Infant incubator
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Importance of Humidity in OR
To dissipate the static electricity to the
risk of explosion.
As higher humidity discomfort to the
personnel.
Keep the humidity of the O.R > 50% but NOT > 60% ?
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Importance of humidity of the
environment around the body
Importance of humidity of the
environment around the body
In order to ↑ the heat loss from the body as in burns and infants in incubator
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Is: The amount of water vapor in the air
Absolute
•Mass of the vapor present in a given volume of air.
•mg/litre g/m3
Relative
•Ratio or % =Actual mass of water vapor present/mass of water vapor required to fully
saturate the air• =actual vapor pressure/S.V.P
Obtained from universal gas law
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T water vapor in the gas and relative humidity.
At 20 C = the air is fully saturated with 17 g/m3
At 37 C = the air is fully saturated with 44 g/m3
Humidity and temperature
So: At 20o C the absolute humidity=17 & the relative =100%.
At 37o C the absolute = 44 & the relative = 17/44=40% (when water content is constant)
The relative = 100% (when AIR IS fully Saturated) Absolute humidity as a function of temperature
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Measurement of humidity(hygrometers)
Relative Absolute Both
- Wet and dry bulb.- Hair tension
- Transducers.- Mass spectrometry.- Weighing
- DEW point “Regnault’s”
The idea: Measurement devices relay on measurement of
some other quantity such as temperature, pressure, mass, mechanical or electrical change in a substance as moisture is absorbed
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Regnault’s hygrometer (Dew point)
The idea: Cooling effect of evaporating ether on the temperature
of a silver tube.
Evaporation of ether is associated with a decrease in the temperature of the tube till reaching the Dew point causing small droplet to condense on the tube.
Dew-point: Temperature at which the
ambient air around tube is fully saturated
Regnault’s hygrometer
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Absolute humidity is obtained by special
tables and graphics containing the
relationship between S.V.P. And H₂O
content of gas.
Relative humidity actual vapor pressure/
S.V.P At that temperature= S.V.P at dew
point/ S.V.P at ambient temperature.
Hair hygrometerThe idea: Increase the hair length when the relative humidity of the
surroundings increases.
The end of the hair is attached to pointer on a scale
It measures relative humidity in the operating room.
Hair hygrometer
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Transducers
Mass spectrometry
The electrical resistance or capacitance of a substance change when the substance absorb water vapor from the surrounding (absolute).
For absolute humidity
Wet and Dry bulb (psychrometer)
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Dry thermometer = ambient temperature.
Wet thermometer = lower temperature
Why?? The cooling effect from the
evaporating water from the wick surrounding the wet bulb (latent heat of vaporization)
The temperature difference is related to the rate of evaporation which is related to relative humidity.(controlled airflow over the thermometer why??)
ControlledAir
Flow
Amb. Air temp.
Wet and dry bulb hygrometer
Weighing
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Cooling of air will condense water vapor
and its quantity = absolute humidity.
Weighing substances before and after the
absorption of vapor (as sulphuric acid).
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Humidifiers
Passive Conserve heat
and water vapor (H.M.E.)
Active Add water
vapor (humidifiers) or
droplets (nebulizers)
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Passive humidifiersHME= artificial nose =condenser humidifier
The form= capsule containing filter with hygroscopic materialThe idea = expiration= water deposited and heat retained.
inspiration= heat and warming of inspired dry gasThe efficiency =70% If high difference in humidity & temperature between cap. and fresh gas flow .
Material= plastic (low thermal conductivity) to preserve temp. inside the cap.
Additives= port for EtCO2 & bacterial filter (HMEF)
Advantage = cheap, light and easy to use.
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Disadvantages ↑the dead space (60ml) thus ↑ the rebreathing
in pediatric patient.
Excess water and secretions obstruction & ↑ in airway resistance
↓ efficiency in large tidal volumes.
Infection (disposable)
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Direct installation of water directly into trachea:
Not recommended- simplest- least efficient.
Disad. rapid and excessive installation aspiration syndrome
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Heated elementH2O dripping on electric heated element up to 100-250◦C vaporization.
Heated H2OIdea: electric heater ↑ temp ↑ capacity of gas to hold H2O vapor. We need also to ↑ temp as latent heat of vaporaization cooling of H2O ↓ Humidification
Efficacy and Adv. The same efficacy -High temp sterility.
Efficacy and advantage Thermostatistically controlled electric heater is most effective ~ 80%. -Used in anaestheisa and ICU as allow inspired gas saturation at body temp. -Antibacterial if temp > 60◦C
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- Heating cause: Thermal injury of the trach. And Lung so use: Thermistor in heater "prevent over heating". Thermometer in humidifier Thermometer for inhaled gas temp. Hyperthermia esp. in pediatrics.
-Infection but …… and…… H2O
Condensation flow obstruction so use H2O trap. for heated H2O
Chemical change to volatile aneth.
gas d. to high heat for heated
element
Disadvantages of both
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Types of heated - H2O 4 types
Passover (large surface area of heated H2O:
Add (wick)
Bubble through:
Sintered glass with tiny holes
Tiny holes at bottom of wide tube (cascade)
Vapor-phase (dry gas mixed with vaporized H2O
23Hot water bath humidifier
NebulizersUltrasonic Gas driven
Vibrating surface within H2O bath very small droplets.
eff most efficient
Idea bernouli effect:• High speed flow of gas pressure drop
H2O to be drawn up (entrained) • Anivl breaks H2O into droplets. • Heater why?!• Efficacy more efficient than heated – H2O
Adv. ↑ freq. of vibrating surface H2O droplet size adjustment. NB. (Idea size ~ 1 micron droplet):
H. of inspired gas Adm. Inhaled drugs (as bronchodilators)
Adv. Humidity as normally found in trachea
Expensive. Supersaturation of inspired gas:H2O over- loading Pulmoy edema (in ped.?)↑ density of gas ↑ resistance to turbulent flow
Disad. Entrainment ratio affected by (back pressure) as in ventilator
NB risk of infection: with all types, so allow: sterile and freq. changed solutions of humidifiers
Gas-driven nebulizer
Plate vibrating at ulrasonic frequency
(e.g.2MHz)
Approximate efficiency of humidifiers; the exact values depend on the model of humidifier in use
Relative Efficiency of Humidifiers
MCQAll are active humidifiers except: Passover H. Cascade H. H.M.E. Nebulizers.
Dew point is a: Pressure at which ambient air is fully saturated. Temp at which ambient air is partially saturated. Temp at which ambient air is fully saturated.
Hygrometer used in the O.R is: Mass spectrometry. Wet and dry hygrometer. Hair hygrometer.
Plz review:
H. and relation to aneasthesia
Dew point and its applications.
Hygrometers
Humdifiers.
Nebulizers
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