Observational Study in Patients Admitted in the Intensive Care Unit.Tracheal Bacterial Load Surveillance in Patients Undergoing Mechanical Ventilation - Assessment of Biomarkers in the Distinction Between Colonization and Infection

The investigators hypotized that:

1. In patients on mechanical ventilation for a non-infectious cause of respiratory failure, the tracheal bacterial load should be absent or below the cut-off values defined for infection, that is to say tracheal colonization.
2. In patients without the diagnosis of Ventilator-Adquired Pneumonia (VAP) and not taking antibiotics till the weaning process, tracheal bacterial load should remain below the predefined cut-off values and the biomarkers (PCT and CRP) should be surrogate markers of this clinical course.
3. In patients developing VAP, an increase in tracheal bacterial load should precede diagnosis with an associated rise in the biomarkers levels (PCT and CRP). Finally, after institution of antibiotic therapy, adequate therapy should be associated with a decrease tracheal bacterial load as well as of the biomarkers (PCT and CRP).
4. In patients admitted with clinical suspicion of pneumonia, either community-acquired (CAP) or hospital-acquired (HAP), with microbiological documentation, after institution of antibiotic therapy, adequate therapy should be associated with a decrease tracheal bacterial load as well as the biomarkers (PCT and CRP).
5. In patients admitted with clinical suspicion of a non-pulmonary infection (e.g. peritonitis and urosepsis) and on mechanical ventilation for an expected length longer than 3 days, either community or hospital-acquired, preferentially with microbiological documentation, after institution of antibiotic therapy, adequate therapy should be associated with a decrease of biomarkers (PCT and CRP).