Changing heat and moisture exchangers after 96 hours rather than after 24 hours: A clinical and microbiological evaluation

Objective: The aim of this study was to determine whether changing heat and moisture exchangers (HMEs) every 96 hrs rather than 24 hrs would affect th eir efficacy to preserve the heat and moisture of inspiratory gases. The im pact of a prolonged use of the HME on its microbial colonization was also a ssessed. Design: Prospective cohort observational study. Setting. Intensive care unit of a university hospital. Patients. Thirteen consecutive patients with no previous history of respira tory disease requiring controlled mechanical ventilation with an HME for >4 days were evaluated. Interventions: The same HME was used for 96 hrs in each patient. Measurements and Main Results: In each patient, during the inspiration phas e, the following measurements were performed: peak and mean airway pressure s, mean values of temperature, and relative and absolute humidity of inspir ed gases. In each patient, measurements were performed after 1 hr of HME us e and then daily up to the fourth day. On days 1 and 4, microbiological sam ples were obtained from the patients' bronchial secretions and the ventilat or side of the HME. After 96 hrs of ventilation with the same HME, tracheal tube occlusion was never observed. Using the same HME for 96 hrs rather th an 24 hrs did not affect its technical performances: temperature at 24 hrs: 32.2 +/- 1.5 degrees C (90.0 +/- 34.7 degrees F), at 96 hrs: 32.1 +/- 1.6 degrees 6 (89.8 +/- 34.9 degrees F); relative humidity at 24 hrs: 91.9 +/- 2%, at 96 hrs: 98.1 +/- 1.7%; absolute humidity at 24 hrs: 33.1 +/- 2.4 mg H2O/L, at 96 hrs: 33.0 +/- 2.5 mg H2O/L. This analysis was based on a total of 312 measurements performed an the 13 patients. Peak and mean airway pre ssures did not change during the 96-hr study period, with identical tidal a nd minute volumes in the study patients. On day 1, ten patients had a posit ive culture of their tracheal secretions at a colony count of greater than or equal to 10(3) colony forming units/mL. After 96 hrs of use with the sam e HME, only seven patients had a positive culture of their tracheal secreti ons, cultures from the ventilator sides of the HMEs were all sterile (13/13 ) after 96 hrs of use. Conclusions: In patients free from previous chronic respiratory disorder an d ventilated for neurologic reasons, changing the HME after 96 hrs rather t han 24 hrs did not affect its technical performance in terms of heat and wa ter preservation of ventilatory gases. There is also some indirect evidence of very little, if any, changes in the HME resistance. No bacterial coloni zation of the ventilator sides of the HMEs was observed after 96 hrs of use . However, other large clinical trials should be undertaken to confirm the safety of extending the time between HME changes.