Impact of Humidification Systems on Ventilator-associated Pneumonia

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Abstract
The respective influence on the incidence of ventilator-associated pneumonia of currently available systems used for warming and humidifying the gases delivered to mechanically ventilated patients, that is, heated humidifiers and heat and moisture exchanger filters, remains controversial. We addressed this question in a multicenter randomized study comparing heated humidifiers (with heated circuits) and filters in an unselected population of 369 intensive care patients receiving mechanical ventilation for more than 48 h. The diagnosis of pneumonia was confirmed according to strict microbiologic criteria. There was no difference in pneumonia rate between the two groups (53 of 184 [28.8%] versus 47 of 185 [25.4%] for humidifiers versus filters; p = 0.48), or in the incidence density of pneumonia (27.4/1,000 ventilatory days versus 25.3/1,000 ventilatory days for humidifiers versus filters; p = 0.76). The mean duration of mechanical ventilation did not differ between the two groups (14.9 +/- 15.1 versus 13.5 +/- 16.3 days for humidifiers versus filters, p = 0.36). Endotracheal tube occlusion occurred, respectively, in five patients and one patient in the humidifier and filter groups (p = 0.12). Intensive care mortality was identical in the two groups (about 33%). These results suggest that both heated humidifiers and heat and moisture exchanger filters can be used with no significant impact on the incidence of ventilator-associated pneumonia and that other criteria may justify their choice.