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The cost of mechanical ventilation (MV) is high. Efforts to reduce this cost, as long as they are not detrimental for the patients, are needed. MV with heat and moisture exchangers (HME) changed every 48 h is safe, efficient, and cost-effective. Preliminary reports suggest that the life span of these filters may be prolonged. We determined prospectively whether a hygroscopic and hydrophobic HME (Hygrobac-Dar; Mallinckrodt) provided safe and efficient heating and humidification of the inspired gases when changed only once a week. Patients who were considered to require mechanical ventilation for more than 48 h were included in the study. HMEs were initially set for 7 d. Efficient airway heating and humidification were assessed by clinical parameters (number of tracheal suctionings and instillations required, peak airway pressures) and hygrometric measurements performed by psychrometry. Resistance was measured from Day 0 to Day 7. Bacterial colonization of circuits and HMEs was studied. A total of 377 days of mechanical ventilation with 60 HMEs was studied. Clinical parameters and hygrometric measurements did not change between Day 0 and Day 7. Mean absolute humidity was 30.3 +/- 1.3 mg H(2)O/L on Day 0 and 30.8 +/- 1.5 mg H(2)O/L on Day 7 (p = 0.7). Endotracheal tube occlusion never occurred. Three HMEs were replaced prematurely because of insufficient absolute humidity. This rare event occurred only in patients with COPD and after the third day of use. In addition, the absolute humidity delivered by the HMEs was significantly lower in patients with COPD than in the rest of the population. Resistance did not change from Day 0 to Day 7 (2.4 +/- 0.3 versus 2.7 +/- 0.3 cm H(2)O/L/s; p = 0.4). Bacterial samples of both circuits and ventilator sides of HMEs were sterile in most cases. We conclude that mechanical ventilation can be safely conducted in non-COPD patients using an HME changed only once a week, leading to substantial cost savings (about $110,000 per year if these findings were applied to the university-affiliated hospitals in Paris).