Presepsin Biomarker for Ventilator-associated Pneumonia Diagnosis in COVID-19 Patients

This study will be a single center, double blind observational study. Measurements of presepsin blood level will be performed in all patients with interstitial Sars-Cov-2 pneumonia admitted to ICU, at the time of the start of invasive mechanical ventilation and every 48 hours for the first 30 days of ICU stay. Surveillance respiratory samples (endotracheal aspiration) will be performed according to clinical practice (at ICU admission and every Mondays and Thursdays in all patients undergoing invasive mechanical ventilation). In all patients admitted to ICU with invasive mechanically ventilation, a bronchoalveolar lavage with rapid microbiological method (film array for the research of the main respiratory pathogens) will be performed, according to common clinical practice. VAP diagnosis will be made based upon the evidence of new lung infiltrates (chest radiography or chest computed tomography) in association with the presence of a pathogen isolated in the non-invasive respiratory sample with semi-quantitative method, according to IDSA and American Thoracic Society guidelines, as well as the presence of other sign of infection (fever, leukocytosis, worsening of oxygenation). The attending physician in charge of the patient enrolled, clinically making the diagnosis of VAP will be blinded of presepsin levels. As a consequence, during the study period, no variation of the clinical practice applied will be performed, and no influence on the care provided to patients included will be determined by the measurement of plasma presepsin. In the current study, we aim to answer to the following questions: * Does a high level of plasma presepsin in patients with a Sars Cov 2 interstitial pneumonia at the time of ICU admission predict the presence of a bacterial respiratory co-infection? * Do presepsin levels early predict the occurrence of VAP in patients with COVID-19 disease? * Does such variation become evident at the time of VAC, therefore anticipating the diagnosis of IVAC? The latter issue might be particularly important in order to commence antibiotic therapy earlier than the diagnosis of IVAC.