pregnant or breastfeeding woman - indication for immediate tracheal intubation - progressive significant acute circulatory insufficiency - impaired alertness, confusion, restlessness - body mass index > 40 kg/m2 - thoracic trauma or other contraindication to prone position - pneumothorax with single anterior thoracic drain and persistent bubbling - vulnerable person: safeguard of justice, guardianship or authorship known at inclusion

pregnant or breastfeeding woman - indication for immediate tracheal intubation - progressive significant acute circulatory insufficiency - impaired alertness, confusion, restlessness - body mass index > 40 kg/m2 - thoracic trauma or other contraindication to prone position - pneumothorax with single anterior thoracic drain and persistent bubbling - vulnerable person: safeguard of justice, guardianship or authorship known at inclusion