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 http://telemed.shams.edu.eg/moodle

↑ 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

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

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.

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

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

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)

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”

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

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

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

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

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

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

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

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.

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)

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

Heated  element Heated  H2O H2O dripping on electric heated element up to 100-250◦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

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

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

Hot water bath humidifier 23

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

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

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

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.

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

THANK YOU