- unable to achieve a prone position for mobility reasons, - unable to achieve a prone position due to agitation whatever the cause, - with clinical occlusive syndrome in order to limit the risk of inhalation, - having a contraindication to the use of the esophageal catheter, - having signs of respiratory distress or disturbance of consciousness requiring intubation within the next hours, - having hypercapnia indicating the use of non-invasive ventilation (pao2> 50 mmhg), - having severe hypoxemia defined by pao2 / fio2 <100mmhg, - ongoing pregnancy or breastfeeding, - subject to a measure for the protection of justice.

- unable to achieve a prone position for mobility reasons, - unable to achieve a prone position due to agitation whatever the cause, - with clinical occlusive syndrome in order to limit the risk of inhalation, - having a contraindication to the use of the esophageal catheter, - having signs of respiratory distress or disturbance of consciousness requiring intubation within the next hours, - having hypercapnia indicating the use of non-invasive ventilation (pao2> 50 mmhg), - having severe hypoxemia defined by pao2 / fio2 <100mmhg, - ongoing pregnancy or breastfeeding, - subject to a measure for the protection of justice.