Changing a hydrophobic heat and moisture exchanger after 48 hours rather than 24 hours: a clinical and microbiological evaluation

Objective: Complications following ventilation with dry and cold gases may be prevented by the use of artificial noses or heat and moisture exchangers, which are a solution to both the problems of humidification and heat preservation. The aim of the present study was to determine whether changing hydrophobic heat and moisture exchangers (HMEs) every 48 h rather than 24 h would affect their efficacy to preserve the heat and moisture of inspiratory gases. The impact of a prolonged use of the HME on its microbial colonization was also assessed. Design: Prospective observational study. Setting: ICU of a university hospital. Patients: Twelve patients requiring controlled mechanical ventilation for more than 2 days were evaluated. Interventions: The patients were ventilated with a heat and moisture exchanger (HME) (Maxipleat Filter, Europe Medical, France). The hydrophobic HME was placed between the Y-piece and the connecting tube and changed after 48 h of continuous use. Temperature (degrees C), relative humidity (%) and absolute humidity (mgH(2)O/l) were obtained using the capacitive sensor principle. Bacterial colonization (tracheal secretions and ventilator side of the HME) were obtained on days 1 and 2. Measurements and results: After 48 h of ventilation with the same HME, tracheal tube occlusion was never observed. Using the same hydrophobic HME for 48 h rather than 24 h did not affect its technical performance : temperature at 24 h: 32.5 +/- 1.3 degrees C, at 48 h: 32.7 +/- 1.8 degrees C; relative humidity(RH) at 24 h: 99.0 +/- 1.4 %, at 48 h: 99.0 1 1.4 %; absolute humidity(AH) at 24 h: 34.0 +/- 2.4 mgH(2)O/l, at 48 h: 34.4 +/- 3.5 mgH,Oil. Peak and mean airway pressures did not change over the 48-h study period, with identical tidal and minute volumes in the study patients. Total respiratory heat losses were not modified during the 48-h study period (at 24 h: 152 +/- 47 cal/min, at 48 h: 149 +/- 65 cal/min). Evaporative and convective heat losses were not modified either. On day 1, eight patients had positive cultures of their tracheal secretions at a colony count of 10(3) or higher cfu/ml, After 48 h of use of the same HME, only six patients had a positive culture of their tracheal secretions. Cultures from the ventilator sides of the HMEs were all sterile (12/12) after 48 h of use. Conclusions: Changing the hydrophobic HME after 48 h rather than 24 h did not affect its technical performance in terms of heat and water preservation of ventilatory gases. There is also some indirect evidence of very little, if any, change in HME resistance. No bacterial colonization of the ventilator sides of the HMEs was observed after 48 h of use. However other large clinical trials should be undertaken to confirm the safety of extending the time between HME changes.