Bronchoscopies Bronchoalveolar lavage (BAL) BAL of ≤100 mL will be performed on day 1 and 5 post-enrollment. Patients will be eligible for BAL if their PaO2/FiO2 has exceeded 100 mmHg for more than 12 hours and they are intubated with an orotracheal tube with an internal diameter of ≥8.5 mm, or a tracheostomy tube. An (additional) RM will be performed after the fiberoptic bronchoscopic procedure. BAL fluid samples will be used for microbiological cultures, cell count, and the determination of biological markers. On the days of the bronchoscopic procedures, the remainder of blood samples used for routine laboratory tests, will be used for the determination of the concentrations of biological markers in the peripheral blood.