Objective: To demonstrate the effects of heat and moisture exchangers (HME) and heated humidifiers(HH) in preventing ventilator-associated pneumonia (VAP).
Methods: PubMed and Cochrane databases were searched by computer retrieval and manual retrieval to identify relevant randomized controlled trials (RCTs) using HMEs and HHs in preventing VAP from January 1st 1990 to September 1st 2010. Meta-analysis of HME and HH in preventing VAP was conducted using the methods recommended by the Cochrane Collaboration.
Results: Eleven RCTs were included.
Sample size: 1 121 in HME group and 1 101 in HH group. In total, the rate of VAP in HME group and HH group was 14.2% (159/1 121) and 15.9% (175/1 101) respectively, the total relative risk (RR) was 0.88, and 95% confidence interval (95%CI) 0.72-1.07, P=0.21. Compared with HH group, there was not a reduction in the risk ratio of VAP in the HME group. Even in mechanical ventilation(MV) with a duration of at least 7 days for subgroup analysis (8 RCTs, sample size: 834 in HME group and 859 in HH group), the rate of VAP in HME group and HH group was 15.2% (127/834) and 17.5% (150/859) respectively, the total RR was 0.84, 95%CI 0. 58-1.23, P=0.37, suggesting that in MV with a duration at least 7 days, there was also no reduction in the risk ratio of VAP in the HME group.
Conclusion: This study suggests there is not a significant reduction in the incidence of VAP in patients humidified with HMEs during MV, even in patients ventilated for 7 days or longer. This finding is limited by lack of enough RCTs and blinding. Further large sample of high quality RCTs is necessary to examine the wider applicability of HMEs and their extended use.