Inclusion Criteria:  Age 20 to 70 years old. Patients with hypoxemia receiving endotracheal mechanical ventilation therapy. The ARDS diagnostic criteria of Berlin Definition, arterial oxygen tension [PaO2]/fractional inspired oxygen [FiO2] ratio (PaO2/FiO2) <200 mm Hg, recent appearance of bilateral pulmonary infiltrates consistent with edema and no clinical evidence of left atrial hypertension. Within 72 hours after ARDS diagnosis.  Exclusion Criteria:  Pregnancy. Participate in other interventional trials at the same time during the acceptance period. Severe trauma combined with rib fracture or pneumothorax, subcutaneous emphysema, and mediastinal air accumulation within three months. Severe chronic respiratory diseases that require long-term use of oxygen therapy or home mechanical ventilation. Have a history of cachexia or terminal cancer. Use immunosuppressants, chemotherapy or radiation therapy. Contraindications for hypercapnia, such as patients with acute brain injury due to intracranial hypertension or craniotomy.