Eight RCTs (n=1,368) were included.
In terms of study quality, 3 studies reported the randomisation method and 4 studies reported a power calculation. All studies reported baseline similarity between the treatment groups with respect to age, gender, and mean duration of and indication for mechanical ventilation.
VAP was significantly reduced with HMEs compared with HHs (RR 0.69, 95% CI: 0.51, 0.94). No significant heterogeneity was found (P=0.56).
There was no significant difference in VAP between HMEs and HHs for less than 7 days' mechanical ventilation (RR 0.99, 95% CI: 0.59, 1.62), but VAP was significantly reduced with HMEs for 7 days or more of mechanical ventilation (RR 0.57, 95% CI: 0.38, 0.83). There was a significant negative correlation between the RR and duration of mechanical ventilation.
The RR of VAP was 0.64 (95% CI: 0.44, 0.92) in RCTs using a clinical diagnosis of VAP, and 0.83 (95% CI: 0.49, 1.42) in RCTs using a microbiological diagnosis of VAP.