Heat and Moisture Exchanger


  • Heat and Moisture Exchanger aka HME filter


  • humidification and microbiological filtration
  • best used in patients with few secretions, who are not hypothermic, do not have large air leaks and do not have high airway resistance



  • placed in line (between Y-piece and ETT)
  • conservation of heat and moisture on expiration



  • ease of use
  • light
  • can retain their ability to humidify for up to 4 days with minimal change in resistance
  • less cumbersome during transport
  • lower staff workload
  • lower costs
  • decreases ventilatory acquired pneumonia (Kola et al, 2005)


  • contains a layer of foam or paper embedded with a hydroscopic salt such as calcium chloride
  • expired gas cools as it crosses the membrane, resulting in condensation and release of the mass enthalpy of vaporisation to the HME layer
  • on inspiration absorbed heat evaporates the condensate and warms the gas, the hygroscopic salt releases water molecules when the vapor pressure is low
  • warming and humidification is thus regulated by the moisture content of the expired gas and patient’s core temperature
  • a filter layer is also present, either an electrostatically charged or a pleated hydrophobic layer, the latter helps return moisture to the gas as condensation and evaporation occurs between the pleats


  • inability to use with all patients (haemoptysis, tenacious secretions)
  • increased airways resistance
  • increased dead space
  • potential for unrecognized airway obstruction if filter blocks
  • less than full humidification and body temperature
  • drying of secretions
  • not appropriate for patients with large air leaks (bronchopleural fistulae) as a lot of gas is lost from chest

References and Links


Journal articles and textbooks

  • Kelly M, Gillies D, Todd DA, Lockwood C. Heated humidification versus heat and moisture exchangers for ventilated adults and children. Anesth Analg. 2010 Oct;111(4):1072. Review. PubMed PMID: 20870984. [free fulltext pdf]
  • Kola A, Eckmanns T, Gastmeier P. Efficacy of heat and moisture exchangers in preventing ventilator-associated pneumonia: meta-analysis of randomized controlled trials. Intensive Care Med. 2005 Jan;31(1):5-11. Epub 2004 Sep 11. Review. PubMed PMID: 15368038.
  • Lorente L, Lecuona M, Jiménez A, Mora ML, Sierra A. Ventilator-associated pneumonia using a heated humidifier or a heat and moisture exchanger: a randomized controlled trial [ISRCTN88724583]. Crit Care. 2006;10(4):R116. PubMed PMID: 16884530; PubMed Central PMCID: PMC1750976.
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