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 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 ↑ viscosity (mucus plug) + Ciliary dysfunction Dry inspired gases + hypothermia 3 Particularly in Mechanically ventilated I.C.U patient Prolonged anesthesia in pediatrics & geriatrics Infant incubator 4 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. 5 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 6 Is: The amount of water vapor in the air 7 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 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 8 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 - Wet and dry bulb. - Hair tension Absolute - Transducers. - Mass spectrometry. - Weighing Both - DEW point “Regnault’s” 9 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: Regnault’s hygrometer Temperature at which the ambient air around tube is fully saturated 10 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 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 The electrical resistance or capacitance of a substance change when the substance absorb water vapor from the surrounding (absolute). Mass spectrometry For absolute humidity 13 Wet and Dry bulb (psychrometer) 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??) Controlled Air Amb. Air temp. Flow 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 Conserve heat and water vapor (H.M.E.) Active Add water vapor (humidifiers) or droplets (nebulizers) 16 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. 17 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) 18 Direct installation of water directly into trachea: Not recommended- simplest- least efficient. Disad. rapid and excessive installation aspiration syndrome 19 Heated H2O Heated element Idea: electric heater ↑ temp H2O dripping on electric heated ↑ capacity of gas to hold H2O element up to 100-250◦C vapor. vaporization. We need also to ↑ temp as latent heat of vaporaization cooling of H2O ↓ Humidification Efficacy and advantage Efficacy and Adv. Thermostatistically controlled The same efficacy electric heater is most effective ~ -High temp sterility. 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: 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 …… H2O Condensation flow obstruction so use H2O trap. for heated H2O and…… 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 Gas driven Ultrasonic 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 Vibrating surface within H2O bath very small droplets. Adv. Humidity as normally found in trachea Adv. ↑ freq. of vibrating surface H2O droplet size adjustment. NB. (Idea size ~ 1 micron droplet): H. of inspired gas Adm. Inhaled drugs (as bronchodilators) Disad. Entrainment ratio affected by (back Expensive. Supersaturation of inspired gas: H2O over- loading Pulmoy edema (in ped.?) ↑ density of gas ↑ resistance to turbulent flow pressure) as in ventilator eff most efficient 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) 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: 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