Heat and Moisture Exchanger

OVERVIEW

• Heat and Moisture Exchanger aka HME filter

USES

• 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

DESCRIPTION

METHOD OF INSERTION AND/OR USE

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

OTHER INFORMATION

Benefits

• 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)

Mechanism

• 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

COMPLICATIONS/DISADVANTAGES

• 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

Lifeinthefastlane.com

• CCC — Humidification

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.