Inclusion Criteria:  aged 18 to 80 years admitted to intensive care unit with a confirmed diagnosis of ARDS received mechanical ventilation less than 48 hours,  Exclusion Criteria:  contraindications for prone position ventilation Past chronic respiratory diseases (long-term family oxygen therapy for chronic respiratory diseases such as pulmonary fibrosis or COPD) New York Heart Association class above II gave written or witnessed verbal informed consent. Contraindications to the use of EIT (e.g., presence of pacemaker or chest surgical wounds dressing) or prone position (as decided by the attending physician) Impending ECMO (on the basis of clinical judgment, including clinical and physiological parameters).