ObjectiveTo evaluate the efficacy of bacterial filters (BF) to decrease pneumonia associated with mechanical ventilation (MV).DesignProspective, randomized study.SettingA 24-bed medicosurgical intensive care unit in a 650-bed tertiary hospital.PatientsA total of 230 patients who needed MV for >24 hrs.InterventionsA total of 114 patients were ventilated with BF and 116 without BF.MeasurementsThroat swab and tracheal aspirate were taken at the moment of admission and twice a week until discharge. We considered the following infectious events: pneumonia, respiratory infection, which comprises pneumonia or tracheobronchitis, and respiratory colonization–infection complex, which comprises respiratory infection or colonization. All infectious events were classified as endogenous or exogenous based on throat flora.Main ResultsBoth groups of patients (ventilated with and without filters) were similar in age, sex, Acute Physiology and Chronic Health Evaluation II score, diagnostic group, days of MV, and mortality. There was no difference in the percentage of patients who developed pneumonia (24.56% with BF and 21.55% without BF), respiratory infection (33.33% vs. 28.44%), or colonization-infection (42.10% vs. 43.96%). The number of infectious events per 1000 days of MV were also similar in both groups: pneumonia (17.41 with BF and 16.26 without BF), respiratory infection (24.62 vs. 21.48), and colonization-infection (36.63 vs. 36). There were also no differences in incidence of infectious events by MV duration. Likewise, we did not find any differences in the number of exogenous events per 1000 days of MV: pneumonia, 2.40 with BF vs. 1.74 without BF; colonization-infection, 4.20 vs. 4.05.ConclusionsBacterial filters in ventilation circuits neither reduce the prevalence of respiratory infections associated with MV nor decrease exogenous infectious events; thus, their usage is not necessary.