In several studies, routine changing of the ventilator circuits is not recommended [26, [98] [99] [100] [101] [102] [103] [104] . Replacement is required when there is gross soilage and mechanical malfunction [105] . The condensate fluid in the ventilator circuit, which contains high concentration of pathogenic bacteria and a risk factor for VAP, has to be removed regularly [106] . And accidental drainage of condensate into the patient's airway and contamination of caregivers during ventilator disconnection or during disposal of condensate should be avoided. In-line devices with one-way valves, put in place into disposable circuits and emptied regularly, are recommended for collecting condensate [75] . Humidification of the inspired air is an important care in the ventilator management. Humidification may be achieved by active humidifiers (bubble-through or wick) or passive humidifiers (hygroscopic condenser-artificial nose-or heat-moisture exchanger-HME-). In humidification, formation of condensate in tubing and colonization of this condensate with microorganisms is an important risk factor for VAP. HME recycle heat and moisture that reduces the condensate formation and also bacterial colonization in the circuit. Moreover they have bacterial filtration characteristics [34, 98] . They do not need to be changed daily and can be used for at least 48 hours, sometimes for up to 1 week [107, 108] . Also with other advantages (reduced nurses workload, reduced financial cost, and better safety), HMEs are favourable devices in many ICUs. Indeed several investigators [109] [110] [111] [112] reported lower rates of VAP in HME groups than conventional heated-water humidification systems, the effect of HME on the prevention of VAP is still controversial and a recent study showed no significant difference in VAP rates [113] . Furthermore, HMEs increase dead space and resistance to breathing, cause airway occlusion, and more tenacious secretions [34, 98, 104, 111] . Additional studies are needed to identify the benefits of HMEs on infection control of VAP.