2. Dr. Mohamed Sayed Shorbagy Lecturer of Anesthesia and Intensive care
Humidity
Presented By
Dr. Mohamed Sayed Shorbagy
Lecturer of Anesthesia and Intensive care
Faculty of Medicine
Ain-Shams University
2012

3. ↑ viscosity (mucus plug)
Why to care ?
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
↑ viscosity (mucus plug) +
Ciliary dysfunction
hypothermia

4. Particularly in Prolonged anesthesia in pediatrics & geriatrics
Mechanically ventilated I.C.U patient
Prolonged anesthesia in pediatrics & geriatrics
Infant incubator

5. Importance of Humidity in OR
Keep the humidity of the O.R > 50% but NOT > 60% ?
To dissipate the static electricity to  the risk of explosion.
As higher humidity  discomfort to the personnel.

6. 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

7. 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

8. Humidity and temperature
 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
Absolute humidity as a function of 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)

9. Measurement of humidity (hygrometers)
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
Relative
Absolute
Both
- Wet and dry bulb.
- Hair tension
- Transducers.
- Mass spectrometry.
- Weighing
- DEW point “Regnault’s”

10. 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

11. 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. 11

12. Hair hygrometer Hair hygrometer The 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

13. Transducers Mass spectrometry
The electrical resistance or capacitance of a substance change when the substance absorb water vapor from the surrounding (absolute).
Transducers
Mass spectrometry
For absolute humidity

14. Wet and Dry bulb (psychrometer)
Dry thermometer = ambient temperature.
Wet thermometer = lower temperature
Why??
Controlled
Air
Flow
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??)
Amb. Air temp.
Wet and dry bulb hygrometer 14

15. Weighing
Cooling of air will condense water vapor and its quantity = absolute humidity.
Weighing substances before and after the absorption of vapor (as sulphuric acid). 15

16. Humidifiers Passive Active
Conserve heat and water vapor (H.M.E.)
Active
Add water vapor (humidifiers) or droplets (nebulizers)

17. Passive humidifiers HME= artificial nose =condenser humidifier
The form= capsule containing filter with hygroscopic material
The idea = expiration= water deposited and heat retained.
inspiration= heat and warming of inspired dry gas
The 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.

18. 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)

19. Direct installation of water directly into trachea:
Not recommended- simplest- least efficient.
Disad.  rapid and excessive installation  aspiration syndrome 19

20. Heated  element Heated  H2O
H2O dripping on electric heated element up to ◦C  vaporization.
Heated  H2O
Idea: 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 20

21. Disadvantages of both - Heating cause: -Infection but …… and……
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 21

22. 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 22

23. Hot water bath humidifier23

24. Nebulizers
Ultrasonic
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

25. Plate vibrating at ulrasonic frequency (e.g.2MHz)
Gas-driven nebulizer
Plate vibrating at ulrasonic frequency (e.g.2MHz)

26. Relative Efficiency of Humidifiers
Approximate efficiency of humidifiers; the exact values depend on the model of humidifier in use

27. MCQ All are active humidifiers except: Dew point is a:
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.

28. Plz review: H. and relation to aneasthesia
Dew point and its applications.
Hygrometers
Humdifiers.
Nebulizers

29. THANK YOU