Bacterial filters in breathing circuits: an unnecessary cost?

Objective

To analyze the utility of bacterial filters (BF) to prevent the incidence of pneumonia (PN), tracheobronchitis (TB) and tracheal colonization (TC) in patients undergoing mechanical ventilation.

Methods

From 1 July 2000 until 31 March 2001 a prospective and randomized study was realized. Included were all patients admitted in ICU and who required mechanical ventilation for 24 hours or more. At admission to the ICU patients were randomized in two groups (one group ventilated with BF, and another one without them). A throat swab on admission and afterwards twice weekly were taken. Infections were diagnosed according to CDC criteria and classified based on throat flora in endogenous and exogenous. The statistical analysis was realized by chi-square test and Student t-test, and we took values P < 0.05 to consider a significant difference.

Results

Included were 230 patients (59.13% male). Mean age was 57.60 ± 17.21 years. APACHE-II was 15.88 ± 5.18. Mortality was 28.26%. Both groups of patients (114 with BF and 116 without BF) were similar in age, sex, mortality and APACHE-II. No significant differences were found in the percentage of patients who developed PN (24.56% with BF and 21.55% without BF), combined PN or TB (34.21% vs 28.44%), combined PN or TB or TC (42.10% vs 43.96%). Neither in the number of infectious events per 1000 mechanical ventilation-days: PN (17.41 with BF and 16.26 without BF), PN or TB (24.62 vs 20.88), PN or TB or TC (36.63 vs 34.98). Neither in the the percentage of patients who developed infectious events and in the number of infectious events per 1000 mechanical ventilation-days in each group of mechanical ventilation-days. Neither in the number of exogenous events per 1000 mechanical ventilation-days (4.20 with BF and 3.95 without BF).

Conclusions

Bacterial filters in breathing circuits do not reduce the incidence of respiratory infections, neither exogenous events. The employment of bacterial filter may be an unnecessary cost.