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Humidifier Moisture Exchange

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  1. 1. Humidifier Moisture Exchange(HME) filters University of Gondar Department of Anesthesia Girmay F. 1
  2. 2. Presentation outline 1. What is humidity 2. Role of Humidification Gas 3. Measurement of humidity 4. Methods of humidification 4.1. Heat & Moisture Exchanger(HME) Filter 2
  3. 3. 1. What is Humidity ?  Humidity is a measure of the amount of water vapour in a gas/atmosphere . 1. Absolute humidity : is defined as actual mass of water vapour present in a known volume of gas. o Usually expressed in either mg / L (Kg/m3,g/m3) or mmHg (partial pressure). 3
  4. 4.  the absolute humidity of air in the URT in humans is about 34g.m-3 and it reaches a peak of 43g.m-3 as it reaches the alveoli. 4
  5. 5. 2. Relative humidity: the ratio of the mass of water vapour in a given volume of gas to the maximum amount of water vapour that the same gas can hold at the same temperature. OR  Amount of water vapour in a gas, expressed as a percentage of that which could be held by the gas if it were fully saturated at the same temperature. 5
  6. 6. Relative humidity = Actual Water Content H2O Content Fully Saturated % OR R.H. = Actual Vapour Pressure Saturated Vapour Pressure %. 6
  7. 7. 3. Dew point: The temperature at which the relative humidity of the air exceeds 100% and water condenses out of the vapour phase to form liquid . 4.Hygrometer : An instrument used for measuring the humidity of a gas. 5. Hygroscopic material: One that attracts moisture from the atmosphere. 7
  8. 8. 2. Role of Humidification Gas  The air we breathe becomes fully saturated with water vapour as it passes through nose to finally reach the alveoli.  This humidification maintains  Mucosal integrity, Ciliary activity  Prevents the drying of secretions and helps in easy expulsion of respiratory secretions when coughing. 8
  9. 9.  Physiology of air way humidification  Nose breathing at rest ,inspired gases become heated at 36oc and are about 80% to 90% saturated with water vapour by the time reach the carina. Largely due to heat transfer in the nose.  Mouth breathing reduces this to 60 % to 70 % relative humidity. 9
  10. 10.  Heat and moisture content falls from carina to nares, so that the nose typically at 30oC.  A countercurrent mechanism heat and moisture exchange in the airways maximises efficiency, with nasal cooling on inspiration and warming on exhalation.  Tracheal temperature and humidity fall with increased ventilation particularly when the inspired gases are cold and dry .
  11. 11.  If totally dry gases were inspired and fully saturated gases exhaled, the total water loss from ventilation at rest would be about 300 ml/day in the average adult.  Normally about half is retained...30% by the nose and 25% the humidity of inspired room air.  Bypassing the nose with an ETT and not humidifying gases cases maximal losses. 11
  12. 12.  Respiratory losses of both heat and water increase with increased ventilation, hyperthermia, and dry inspired gases.  Cilia paralysis and reduced rates of mucus flow occur below 50% relative humidity at 37 °C. 12
  13. 13.  Lack of humidification (e.g. ventilating a patient with dry gas through a tracheal or tracheostomy tube) can result  in cracking of mucosa, drying of secretions  keratinisation of the tracheo -bronchial tree  Reduction in ciliary activity, atelectasis and infection. 13
  14. 14.  Over-humidification has its own complications.  It can result in water intoxication, especially in neonates and infants in intensive care.  water clogging and airway burns. 14
  15. 15.  Ideal properties of humidifier :  Efficient and easy to use.  have low resistance to flow of gas, and should be economical and safe.  Humidification can be used with any breathing circuit and may be provided for air, oxygen and a mixture of gases including anaesthetic gases. 15
  16. 16. 3. Measurement of Humidity  Measured using hygrometer ; most Measure relative humidity  1. Hair hygrometer :  This is based on the principle that the length of the hair increases with increasing humidity.  It is fairly accurate between 30 and 90%. 16
  17. 17. 2. Wet and dry bulb Hygrometer:  Two mercury thermometers, one in ambient temperature and the other in contact with water through a wick are used.  The difference in the temperature reading in these two thermometers is a measure of rate of evaporation of water, that in turn depends on humidity. 17
  18. 18. 3. Regnault’s hygrometer • Air is blown through a silver tube containing Ether. • At dew point , condensation occurs on the outer surface of the tube. Ambient air is fully saturated at this temperature. • The ratio of saturated vapour pressure (SVP) at dew point to SVP at ambient temperature gives Relative humidity. 18
  19. 19. 4. Mass spectrometer: o This instrument uses the principle of reduction in the ultraviolet light transmitted through the medium containing water vapour. 19
  20. 20. 4. Methods of humidification  Heat and moisture exchanger(HME) filter  Water bath humidifier  Nebulizers/ Nebulisers 20
  21. 21. 4.1. Heat & Moisture Exchanger(HME) Filter  HME filters contain materials such as ceramic fiber, paper, cellulose, fine steel or aluminum fibers in a hygroscopic medium such as calcium chloride or silica gel . 1. Warm, humidified, expired gas passes through the HME, water vapour condenses within the medium and is then re- used for humidification of the inspired gas. 21
  22. 22.  The HME is warmed by the latent heat of water condensing on it. This heat is also released during subsequent inspiration. 2. Minimize transmission of bacteria and viruses filtering properties with efficiencies more than 99.9977.  They protect : patient, breathing circuit, anaesthetic machine and ventilator. 22
  23. 23.  The microbial filtering property may be due to: 1. Direct interception: If the particle is more than 1µm (micrometer), it is physically prevented from passing through the pores. 2. Inertial impaction :Smaller particles (<0.5µm) are held by the filtering medium by van der Waals electrostatic forces. 23
  24. 24. 3. Diffusion interception: Particles less than 0.5mcm move freely and randomly (Brownian movement) and subsequently swell up and get filtered by the pores. 4. Electrostatic attraction: Charged particles are attracted by oppositely charged fibres. 24
  25. 25.  The main advantages of HME filters are:  Easy to use in breathing circuits.  Cheap and disposable.  60-70% relative humidity achieved.  Temperature achieved ranges from 29-34 ̊C.  Can be incorporated as a microbial filter. 25
  26. 26.  The main disadvantages  Need replacing every 24 hours (maximum).  Secretions can block the filter.  Resistance to flow of gas can be up to 2cmH2O.  Can add to the weight of the circuit – may be significant in neonates /infants.  Increase circuit dead space. 26
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  28. 28.  2 ports (tubing connections) • sampling port for capnography  Filtration element :  Felt-like electrostatic material  Pleated hydrophobic material 28
  29. 29. Summery  HME filters and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways.  Humidity is an imp’t aspect of delivering gases to patients in operating theatres and ICU.  The consequences of not humidifying gases can be serious in particular patients. 29
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