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