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Does the use of heat and moisture exchangers rather than heated humidifiers affect the incidence of ventilator associated pneumonia?

Citation: Kollef HM, et al. Condenser Humidifier With Heated-Water Humidification in Mechanically Ventilated Patients. Chest 1998; 113:759-67

Lead author's name: MH Kollef

Three-part Clinical Question:

Patients:  intensive care patients requiring mechanical ventilation

Intervention: hydroscopic heat & moisture exchanger v. heated humidifier

Outcome: incidence of ventilator-associated pneumonia

Search Terms: Intensive care, critical care, mechanical ventilation, ventilator associated pneumonia, nosocomial pneumonia, heat & moisture exchanger, heated humidifiers, controlled trial

The Study: Randomised controlled trial, blinded, analysis on completion of study

The Study Patients: 310 intensive care patients having mechanical ventilation

Control group: N = 147; all analysed

Experimental group: N = 163; all analysed. 21 patients who were ventilated > 7 days were changed to heated water humidification, as per study protocol

The Evidence:

Comments:

Consecutive ventilated patients were randomised to the two groups. Patients were followed up during the episode of ventilation. However it is not known how many patients acquired pneumonia during the first 2 days of admission. Therefore some patients with community-acquired pneumonia were incorrectly labelled as having ventilator-associated pneumonia. Furthermore, 21 patients who were ventilated for > 7 days in the HME group were given heated water humidification as determined by the study protocol. These patients who would be expected to have a high incidence of VAP, crossed over to the control group, yet were analysed as being in the experimental group.

Diagnosis of pneumonia was based on clinical criteria and made by an infection control nurse, apparently blinded to the treatment received.

The groups were similar at the start of the trial and apart from the study intervention received similar treatment.

The study was powered to provide an 80% chance of detecting a 15% difference in pneumonia rates between the two groups.

Hydroscopic HMEs are not as effective bacterial filters as hydrophobic devices and may not provide sufficient protection from the aspiration of contaminated ventilator circuit contents.

Appraised by: Dr David Swann, Consultant, Intensive Care, Royal Infirmary of Edinburgh. David Swann
Email: d.g.swann@ed.ac.uk

Kill or Update By: December 2009

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