Individualized Perioperative Open-lung Ventilatory Strategy With High Versus Conventional Inspiratory Oxygen Fraction (iPROVE-O2).

Inclusion Criteria: * Age not less than 18 * Planned abdominal surgery\> 2 hours. * Signed informed consent for participation in the study. Exclusion Criteria: * Age less than 18 years. * Pregnant or breast-feeding. * Patients with BMI \>35. * Syndrome of moderate or severe respiratory distress: PaO2/FiO2 \< 200 mmHg. * Heart failure: NYHA IV. * Hemodynamic failure: CI \<2.5 L/min/m2 and / or requirements before surgery ionotropic support. * Diagnosis or suspicion of intracranial hypertension (intracranial pressure\> 15 mmHg). * Mechanical ventilation in the last 15 days. * Presence of pneumothorax. Presence of giant bullae on chest radiography or computed tomography (CT). * Patient with preoperatively CPAP. * Participation in another experimental protocol at the time of intervention selection.