To evaluate in a cohort of patients on mechanical ventilation, for non-infectious reasons and for documented sepsis of pulmonary as well as non-pulmonary origin, the bacterial load, procalcitonine (PCT), C-Reactive Protein (CRP), temperature, White cell count (WCC), American College of Chest Physicians/Society of Critical Care Medicine (ACCP/SCCM) consensus conference criteria, Sequential Organ Failure Assessment score (SOFA) and simplified Clinical Pulmonary Infection Score (CPIS) through the mechanical ventilation period

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).

Inclusion criteria:

• Patients admitted in the ICU, with an expected length of mechanical ventilation > 3 days.
• Not receiving antibiotics for >24 hrs before ICU admission- An expected length of mechanical ventilation > 3 days

Exclusion Criteria:

• Patients <18 yrs old
• Pregnancy and lactation
• Fulminant hepatic failure
• Pancreatitis
• Patients with the diagnosis of disseminated cancer, expected to die or undergo withdrawal of treatment within 72 hours after enrolment.

Patients admitted in the ICU