Bacterial colonization and infections of the lower respiratory tract in an interdisciplinary ICU

Introduction

Tracheal intubation and mechanical ventilation are often associated with infection of the lower respiratory tract (LRT). The morbidity associated with the progression of airway colonization (AC) to ventilator-associated tracheobronchitis (VAT) and from VAT to ventilator-associated pneumonia (VAP) has been analyzed but not been fully elucidated. We endeavored to study the relationship between AC and development of infections (VAT and VAP) of the LRT in ICU patients.

Methods

Retrospective study of 400 consecutive ICU patients ventilated >48 hours in the past 4 years. Patients age, gender, APACHE II, prior illness, cause of admittance, length of stay (LOS), time of mechanical ventilation (MV), outcome, time of appearance of AC and infection of the LRT were registered. MODS and CPIS were measured at onset of infection (VAT-VAP) and 3 days after. MODS was also calculated on the day AC appeared. Bronchial secretions were cultured at admission, at least once a week and whenever there was a change in the amount and quality of bronchial secretions or clinical infection was suspected. The Mann-Whitney test was used for statistical analysis and statistical significance was set at P < 0.05.

Results

From the 400 studied patients 68 (17%) were colonized and 153 (48.25%) developed infections: 54 (13.5%) VAT and 99 (24.7%) VAP. Colonization appeared after 3.1 ± 0.8 days of ICU admission exclusively with Gram-negative microorganisms. Twenty-five (36.7%) of the colonized patients developed infections of the LRT (with the same pathogen): 8 (11.7%) VAT after 4.6 ± 2.7 days and 17 (25%) were diagnosed with VAP after 9.8 ± 1.8 days. From the eight VAT patients, four developed VAP (50%) after 5.4 ± 0.4 days. None of the colonized patients died. The colonized patients who developed infections were elderly (P < 0.05), more severely ill (P < 0.04) and had at the time of infection a diagnosis higher temperature (P < 0.01), more severe leukocytosis (P < 0.02) but not statistically significant organ dysfunction (P > 0.3). The appearance of VAP caused more severe organ dysfunction (P < 0.002), longer MV duration (P < 0.01) and longer LOS (P < 0.001) but did not influence mortality. On the day of AC detection MODS was 2.4 ± 0.5, on VAT detection MODS was 4.8 ± 0.9 and on VAP appearance MODS was 9.6 ± 0.7. CPIS at VAT detection was 3.9 ± 0.9 and at VAP detection 6.1 ± 0.5 (day I) and 7.2 ± 0.8 (on day III).

Conclusions

AC resulted in LRT infections in only one-third of our patients and the majority of LRT infections are not preceded by AC.