Ventilator-associated pneumonia using a heated humidifier or a heat and moisture exchanger : a randomized controlled trial [ ISRCTN 88724583 ]

Introduction Some guidelines to prevent ventilator-associated pneumonia (VAP) do not establish a recommendation for the preferential use of either heat and moisture exchangers (HMEs) or heated humidifiers (HHs), while other guidelines clearly advocate the use of HMEs. The aim of this study was to determine the incidence of VAP associated with HHs or HMEs. Methods A randomized study was conducted in the intensive care unit of a university hospital involving patients expected to require mechanical ventilation for >5 days. Patients were assigned to two groups; one group received HH and the other group received HME. Tracheal aspirate samples were obtained on endotracheal intubation, then twice a week, and finally on extubation, in order to diagnose VAP. Throat swabs were taken on admission to the intensive care unit, then twice a week, and finally at discharge from the intensive care unit in order to classify VAP as primary endogenous, secondary endogenous, or exogenous. Results A total of 120 patients were assigned to HMEs (60 patients) and HHs (60 patients); 16 patients received mechanical ventilation for less than five days and were excluded from the analysis. Data analysis of the remaining 104 patients (53 HMEs and 51 HHs) showed no significant differences between groups regarding sex, age, Acute Physiology and Chronic Health Evaluation II score, pre-VAP use of antibiotics, days on mechanical ventilation, and diagnosis group. VAP was found in eight of 51 (15.69%) patients in the HH group and in 21 of 53 (39.62%) patients in the HME group (P = 0.006). The median time free of VAP was 20 days (95% confidence interval, 13.34–26.66) for the HH group and was 42 days (95% confidence interval, 35.62–48.37) for the HME group (P <0.001). Cox regression analysis showed the HME as a risk factor for VAP (hazard rate, 16.2; 95% confidence interval, 4.54–58.04; P < 0.001). Conclusion The patients mechanically ventilated for more than five days developed a lower incidence of VAP with a HH than with a HME. Introduction The use of mechanical ventilation with an artificial airway requires conditioning of the inspired gas [1]. This conditioning is necessary because medicinal gases are cold and dry, and when the upper airway is bypassed it cannot contribute to the natural heat and moisture exchange process of inspired gases. At low levels of inspired humidity, water is removed from mucous and the periciliary fluid by evaporation, causing increased viscosity of mucous and loss of the periciliary fluid layer. Mucociliary clearance therefore decreases since the thick mucous is difficult for cilia to remove; also, mucociliary transport is impaired due to a decreased cilia beat rate. Continuous desiccation of the mucosa causes cilia paralysis, cell damage, and decreased functional residual capacity, and atelectasis may develop. Artificial humidification of medicinal gases can be active or passive. In active humidifiers, known as heated humidifiers (HHs), the inspired gas passes across or over a heated water bath. Passive humidifiers, known as artificial noses or heat and moisture exchangers (HMEs), trap heat and humidity from the patient's exhaled gas and return some to the patient on the subsequent inhalation.