This study tested the potential value of routine microbiological cultures before VAP onset in predicting the causative pathogen of VAP and in anticipating the correct antibiotic choice. Authors cultured blood, respiratory secretions, catheter-tips, urine, and others substances, and found that there was no relationship between the colonization of tissues other than from the lungs and the etiology of VAP. High-quality distal bronchial samples obtained by BAL and protected-specimen brush, if cultured in the previous 72 h, had positive predictive values of 25% and 28%, respectively. Only distal respiratory secretions, when repeated at intervals between 48 and 72 h, might have a role in predicting the causative bacteria of VAP. Special attention is required for potentially drug-resistant bacteria like methicillin-resistant Staphylococcus aureus, P aeruginosa, and Acinetobacter baumannii with positive predictive values of 62%, 52%, and 24%, respectively. Previous colonization with any of these pathogens implies a high risk for subsequent pneumonia, allowing for an adequate empiric antibiotic selection.
The authors present the largest study performed in the United States, comprising 842 VAP patients and 2,243 control subjects. The mean interval between intubation and the identification of VAP was 3.3 ± 6.6 days. A crude incidence of 9.3% was found in ventilated patients. The authors also reported morbidity and economic variables resulting in an increase in mean ICU and hospital stays (6.1 days), mean period of mechanical ventilation (9.6 days), and a mean doubled increase in hospital charges ($41,294). P aeruginosa was isolated most frequently in patients with VAP, occurring > 4 days after the start of mechanical ventilation (19.7%), while S aureus was isolated most frequently in patients in whom VAP was diagnosed before the fourth day of onset of mechanical ventilation (23.7%). They found no attributable mortality at 30 days. An outstanding conclusion is that intermediate underlying illness severity is one of the independent risk factors for developing VAP, as reported previously for late-onset VAP episodes caused by P aeruginosa. The main goal of this study concerned the impact on the design of future studies aimed at VAP prevention.