Hyperoxemia and Ventilator-associated Pneumonia

The aim of this prospective cohort single-center observational study is to determine the impact of hyperoxemia on ventilator-associated pneumonia (VAP) occurrence. * SpO2 will be continuously recorded in order to determine the percentage of time spent with hyperoxemia. * Patients with VAP will be prospectively identified. * Patient characteristics and risk factors for VAP will be prospectively collected. * Oxidant stress will be prospectively investigated in study patients: glutathion peroxidase (GPX), plasmatic superoxyde dismutase (SOD), total plasmatic antioxidant status (SAT) and urinary 8-isoprostanes will be performed at ICU admission, once a week, and at VAP occurrence. Patients with VAP will be compared with those with no VAP