Heat and moisture exchanging filters and pneumonia: many unresolved questions

Background and objective: The use of heat and moisture exchanging filters ( HMEF) instead of conventional heated humidifiers is a cost-effective method in intensive care medicine. It was the objective of this paper to investig ate the evidence for HMEF from the viewpoint of prevention of pneumonia and to investigate the appropriate changing intervals as well as filter materi als. Method: Randomised controlled trials published in recent years and focusing on prevention of pneumonia as well as other prospective controlled studies were reviewed systematically. Results: The studies demonstrate neither a clear advantage nor disadvantage of HMEF. No final statement is possible concerning changing intervals and the most appropriate filter materials. However, the data give some evidence for a possible extension of changing intervals to 72 hours without harm to the patients and probably show very little influence of filter materials. Conclusion: Because of the economic advantages of HMEF instead of an active humidification, the use of filters - with the exception of contra indicati ons for individual patients - should be preferred.