• Robert J Boots, Narelle George, Joan L Faoagali, John Druery, Kevin Dean, and Richard F Heller.
• Department of Intensive Care Medicine, Royal Brisbane and Women's Hospital, Brisbane, Australia, and Department of Public Health, Manchester University, United Kingdom.
• Crit. Care Med. 2006 Mar 1; 34 (3): 687-93.

ObjectiveTo compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW).DesignA prospective, randomized trial.SettingA metropolitan teaching hospital's general intensive care unit.PatientsThree hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs.InterventionsPatients were randomized to humidification with use of an HME (n=190), SHW (n=94), or DHW (n=97).Measurements And Main ResultsStudy end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p=0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p=.03) and ventilation days (AOR, 1.05; 95% CI, 1.0-1.2; p=.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% CI, 0.4-0.2; p=.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p=.2), as were suction frequency, secretion thickness, and blood on suctioning (p=.32, p=.06, and p=.34, respectively). The HME use per patient per day was 1.13.ConclusionsHumidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use.

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