HME vs. Heated Humidity in ALI/ARDS

Posted on March 29, 2006 by jeffd

Heat & moisture exchangers (HME) and heated humidifiers (HH) have long been compared in terms of adequate gas humidification, secretion accumulation and VAP incidence for example. A recent article in Intensive Care Medicine took a look on their effect on gas exchange and the respiratory system in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients.

Heat and moisture exchangers and heated humidifiers in acute lung injury/acute respiratory distress syndrome patients. Effects on respiratory mechanics and gas exchange.
Indalecio Morán, Judith Bellapart, Alessandra Vari and Jordi Mancebo. Intensive Care Med. 2006 Apr;32(4):524-31.

The study took place in 3 phases:

  1. patients were ventilated with HME at baseline settings
  2. settings were maintained and the HME was replaced with HH
  3. using HH, the tidal volume (Vt) was changed until baseline PaCO2 levels were reached, all other settings (PEEP, rate etc.) were kept unchanged

ALI/ARDS diagnosis was made based on America-European Consensus Conference definition and the HME used was an Edith Flex with a dead-space of 90ml.

By using HH instead of HME and without changing Vt, PaCO2 decreased from 46 to 40 mmHg and physiological dead-space decreased from 352 to 310. Comparing the first phase with the third, Vt decreased from 521 to 440 ml without significant changes in PaCO2, plateau airway pressure decreased from 25 to 21 cmH2O and respiratory system compliance improved from 35 to 42 ml/cmH2O. PaO2 remained unchanged in the three phases. (mean values listed)

This study nicely shows that by simply using HH instead of an HME in ALI/ARDS patients reduces dead-space lowering PaCO2, this allows the patient to be ventilated with lower tidal volumes and lower plateau pressures. In this study the lower tidal volumes significantly improved respiratory compliance in the patients.

Although the differences in PaCO2 were only moderate, increasing the respiratory rate to compensate for the dead-space from the HME may induce gas trapping and auto-PEEP or simply may enhance ventilator-induced lung injury.

Given that low tidal volume ventilation with plateau pressures has been shown to improve mortality in ALI/ARDS patients I think we need to carefully consider which humidity device is used for these type of patients.

Filed under: ARDS, Ventilators

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2 Responses to “HME vs. Heated Humidity in ALI/ARDS”

  1. RJ, RCP, on April 5th, 2007 at 4:43 am Said:

    HAS THERE BEEN ANYMORE STUDIES DONE ON THIS BESIDES THE PRESENT ONE TO BACK UP THE INFORMATION LISTED?

  2. jeffd, on April 5th, 2007 at 7:53 am Said:

    Other studies that I am aware of are:

    The effects of apparatus dead space on P(aCO2) in patients receiving lung-protective ventilation.
    Hinkson CR, Benson MS, Stephens LM, Deem S.
    Respir Care. 2006 Oct;51(10):1140-4.

    Influence of the humidification device during acute respiratory distress syndrome.
    Prat G, Renault A, Tonnelier JM, Goetghebeur D, et al.
    Intensive Care Med. 2003 Dec;29(12):2211-5.

    Ability and safety of a heated humidifier to control hypercapnic acidosis in severe ARDS.
    Prin S, Chergui K, Augarde R, Page B, et al.
    Intensive Care Med. 2002 Dec;28(12):1756-60.

    Maybe I should do a comprehensive review of all the studies that relate to this topic, as it seems to be one of interest for many therapists.

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