Failure of bacterial filters to reduce respiratory infection incidence

Objective

To evaluate the efficacy of bacterial filters (BF) in breathing circuits to reduce the incidence of tracheal colonization (TC), tracheobronchitis (TB) and pneumonia (PN) in patients undergoing mechanical ventilation (MV).

Design

Prospective, randomized study.

Setting

A 20-bed medical-surgical Intensive Care Unit (ICU).

Patients

All patients admitted in ICU from 16-6-2000 to 16-10-2000 and who required mechanical ventilation for 24 hours or more.

Intervention

At admission to the ICU, patients were randomly assigned to one of two groups. In one group, patients were ventilated with bacterial filter, in the other group, were ventilated without bacterial filter. We collected data on surveillance samples from throat on admission and afterwards twice weekly, and respiratory infections during the ICU stay. Infections were diagnosed according to the criteria of the CDC and classified bassed on throat flora [1] in: primary endogenous, secondary endogenous and exogenous (Ex).

Statistical analysis

The statistical significance of the variables was tested using Chi-square test or Student's t-test where appropriate. Values P < 0.05 were considered statistically significant (S).

Results

Eighty-seven patients fulfilled all criteria (62.06% man). Mean age was 57.58 ± 16.56 years, APACHE-II 15.99 ± 5.66. Mortality was 21.83%. Patients ventilated with bacterial filter were 45 and 42 patients were ventilated without bacterial filter. Both groups of patients were similar in age, sex, mortality, days of mechanical ventilation and APACHE-II. Patients ventilated with bacterial filter (62.22% males) had APACHE-II 16.27 ± 5.90, with 13.13 ± 14.29 days of mechanical ventilation (total = 591 days) and mortality was 22.22%. Patients ventilated without bacterial filter (61.90% males) had APACHE-II 15.72 ± 5.42, with 18.50 ± 23.66 days of mechanical ventilation (total = 777 days) and mortality 21.42%. Developed pneumonia in 31.11% patients with BF and 33.33% without BF (P = no S). The number of tracheal colonization (TC), tracheobronchitis (TB) and pneumonia (PN) in patients undergoing mechanical ventilation (MV) with bacterial filter (BF) and without bacterial filter (no BF) per 1000 mechanical ventilation-days were the following:

Table 1

Conclusions

Bacterial filter in breathing circuits do not reduce the incidence of tracheal colonization, respiratory infections or exogenous events.