Critically-ill Patients Admitted to the ICU for Acute Respitatory Failure, Regardless the Aetilogy

This study aims to Primary Aims: Verify the predictability of the PLIS at admission in predicting major clinical outcomes including: * ICU mortality (or discharge) and time to death (or discharge) * Escalation of ventilatory support antibiotic therapy or supportive medications (inotropes, steroids, sedation, neuromuscular blockers). Secondary Aims: * Determine the correlation between initial PLIS and the degree of disease severity (as evaluated per SOFA and APACHE II scores) * Determine the correlation between initial PLIS and partial pressure of oxygen in arterial blood (PaO2) to Fraction of inspired oxygen (FiO2): PaO2/FiO2 * Explore the potential association between the type of ventilatory support, ventilatory settings and PLIS at different time points. * Verify whether the site of consolidation (anterior vs. posterior lung zones) can reliably predict mortality in in ALI patients. * Determine the correlation between the PLIS score and the degree of ALI as quantified by CT of the chest (whenever a CT study is available) at the time of admission.