Study objective: To evaluate the importance of the
different pathogenic pathways involved in the development of
ventilator-associated pneumonia (VAP).
Setting: An 18-bed medical and
Patients: One hundred twenty-three
patients receiving mechanical ventilation (MV).
Interventions: Tracheal, pharyngeal, and gastric samples
were obtained simultaneously every 24 h. In cases where VAP was
suspected clinically, bronchoscopy with protected specimen brush and
BAL were performed. Semiquantitative cultures of pharyngeal
samples and quantitative cultures for the remaining samples were
Results: Tracheal colonization at
some time during MV was observed in 110 patients (89%). Eighty
patients had initial colonization, 34 patients had primary
colonization, and 50 patients had secondary colonization. Nineteen
patients had VAP, and 25 organisms were isolated. For none of these
organisms was the stomach the initial site of colonization.
Gram-positive organisms colonized mainly in the trachea during the
first 24 h of MV (p < 0.001). On the contrary, enteric
Gram-negative bacilli (p < 0.001) and yeasts (p < 0.002)
colonized the trachea secondarily. Previous endotracheal intubation
(p < 0.005) and acute renal failure before admission to the ICU
(p < 0.001) were associated with colonization by Pseudomonas
aeruginosa; prior antibiotics were associated with colonization
by Acinetobacter baumanii (p < 0.05) and yeasts
(p < 0.006); and cranial trauma was associated with
Staphylococcus aureus colonization
(p < 0.035).
Conclusions: Although the
stomach can be a source of organisms that colonize the tracheobronchial
tree, it is a much less common source of the bacteria that cause VAP.
The pattern of colonization and risk factors may be different according
to the type of organisms involved.