ObjectiveTo determine whether use of a hygroscopic heat and moisture exchanger (HME) for 48 hrs without change affects its efficiency and the level of bacterial colonization in long-term mechanically ventilated medical intensive care unit patients.DesignProspective, randomized clinical study evaluating two hygroscopic HMEs.SettingMedical intensive care unit at a university teaching hospital.PatientsLong-term mechanically ventilated medical intensive care unit patients, including chronic obstructive pulmonary disease patients.InterventionsPatients were randomly allocated to one of the two HMEs studied (Hygrolife and EdithFlex) and changed every 48 hrs. Devices in both groups could be changed if hygrometric measurements indicated insufficient humidity delivery.Measurements and Main ResultsDaily measurements of inspired gas temperature and relative and absolute humidity. In addition, cultures of tracheal aspirations and both patient and ventilator sides of the device were performed after 48 hrs of use. Ventilatory variables and clinical indicators of efficient humidification were also recorded. Prolonged use of both HMEs was safe and efficient (no tracheal tube occlusion occurred). Mean duration of mechanical ventilation was 20 days. Both clinical indicators and hygrometric measurements showed that both devices performed well during 48 hrs. Absolute humidity with EdithFlex was significantly higher on day 0 and day 1 than with Hygrolife. Absolute humidity measured in chronic obstructive pulmonary disease patients was identical to that measured in the rest of the study population. Tracheal colonization and HME colonization were similar with both HMEs. Bacterial contamination of the ventilator side of both devices was markedly low.ConclusionsThese two purely hygroscopic HMEs provided safe and efficient humidification during a 48-hr period of use in long-term mechanically ventilated medical intensive care unit patients, including chronic obstructive pulmonary disease patients. In addition, they maintained ventilatory circuits clean, despite the absence of filtering media. The cost of mechanical ventilation is consequently reduced.