Humidity and Aerosol Therapy Equipment

Chapter 3 Humidity and Aerosol Therapy Equipment  Physics of Humidity and Aerosol Therapy Humidity – Is water that is in the gaseous state – Behaves in a similar way to gas molecules Exerts Pressure & is in constant random motion –...

Chapter 3 Humidity and Aerosol Therapy Equipment  Physics of Humidity and Aerosol Therapy Humidity – Is water that is in the gaseous state – Behaves in a similar way to gas molecules Exerts Pressure & is in constant random motion – When calculating the partial pressure of a gas containing humidity, the partial pressure of water vapor must be accounted for. Dalton’s Law of Partial Pressures Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 2  Physics of Humidity and Aerosol Therapy (continued) Aerosols – Particulate matter suspended in a gas Measurement of Humidity – Water content or absolute humidity – Relative humidity – Evaporation – Humidity deficit Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 3  Water Content or Absolute Humidity Measured in g or mg of water Partial P of water is constant regardless of barometric P – Depends on T0 & relative humidity When fully saturated… – Maximum absolute humidity or capacity Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 4  Relative Humidity Expressed as % of water capacity Formula: Actual Humidity Capacity Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 5  Evaporation Water moving from liquid gaseous state Molecules escape liquid & become gas – Overall energy level & T0 declines – Higher T0 = more energy = more escape Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 6  Humidity Deficit Difference b/t inspired gas content & content of gas @ BTPS – 370C, 43.9 mg/L, 47 mmHg Clinically significant if it is large & sustained – Retained secretions – Airway plugging – Obstruction – infection Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 7  Humidity Therapy Equipment Humidifier: adds water vapor to a gas Factors Influencing Humidifier Efficiency – Temperature: warmer liquid = more molecules entering gaseous state + can hold more water – Surface area: more surface area = more humidity – Time for contact: more time = more humidity Cannot slow gas flow if patient requires it! Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 8  Clinical Application of Humidity Therapy AARC Clinical Practice Guideline: Humidification during Mechanical Ventilation – The humidifier should provide a minimum of 30 mg H2O/L of delivered gas at 30°C. Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 9  Clinical Application of Humidity Therapy (continued) – When using a heated humidifier, appropriate monitoring should include temperature probe(s) at the humidifier and the airway to monitor heat output Condensation on temp probes can cause overheating! Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 10  Humidifiers Room Humidifier Bubble Humidifier Pass-Over Humidifier – Simple Reservoir – Wick – Membrane Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 11  Room Humidifier Actually an aerosol generator Large potential for infection – Moves large amounts of air – Large H2O reservoir is good place for bacterial growth – Must be kept clean! Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 12 Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 13  Bubble Humidifier Deliver 33-40% relative humidity @ 370 C – L flow – Ambient T0 – Time of operation Built-in pop-off valve @ 2 psi – May have “whistle alarm” Diffuser breaks gas into small bubbles, surface area Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 14 Examples of Bubble Humidifiers 15 Examples of Bubble Humidifiers 16  Heated Bubble humidifiers are available However, most are not heated. 17  Pass-Over Humidifier Gas flow passes over H2O reservoir or H2O saturated material Water evaporates into the gas – T0 = can hold more H2O Types – Simple reservoir model – Wick units – Membrane devices 18  Passover Humidifiers Simple reservoir – Gas flows over surface of volume of water – Usually used as heated system to provide humidity to mechanically ventilated patients Wick humidifier – Gas passes over or through water saturated material – Usually heated system used with mechanical ventilation Membrane humidifier – H2O is allowed to pass through a membrane, leaves behind contaminants – Vapotherm Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 20  Condensation Gas cools as it leaves humidifier Lower temperature = lower carrying capacity Condensate collects in tubing Factors that affect amount of condensate Temperature difference across system Ambient temperature Gas flow Set airway temperature Can be minimized with placing water traps at lowest point in circuit. use of heated-wire circuit.  Drainage Bag Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 22  Heated Circuit w/ Humidifier Heated circuit aims to maintain temperatue to minimize condensation “Rainout” Servo heater = digitally controlled via feedback from sensors Copyright ©2005 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 23  Heat & Moisture Exchangers (a.k.a. artificial nose) Absorbs heat & moisture from exhaled gas, then returns it to inhaled gas – 70-90% relative humidity @ 30-310 C R dramatically w/ mucous Short-term usage (