No clear recommendation exists for the level of oxygenation of intensive care patients. In Acute Respiratory Distress Syndrome (ARDS), pulsed oxymetry (SpO2) have to be kept between 88 and 95 percent and oxygen alveolar pressure between 55 and 80 mmHg (PaO2). These recommendations are common but do not lie on high scientific knowledge and level of proof. In the major studies of these fifteen last years that changed ARDS management, PaO2 was kept around 85 and 90 mmHg despite current recommendations of 55 to 80 mmHg of PaO2.