Inclusion Criteria:  Age 18-85 years old Meet ARDS Berlin diagnostic criteria Artificial airway has been established (tracheal intubation, tracheotomy) Sign informed consent Within 7 days of diagnosis of ARDS  Exclusion Criteria:  Younger than 18 years old or older than 85 years old Pregnant women, cancer and immune system diseases There are contraindications for bronchoscopy (poor oxygenation/severe heart disease, cardiac insufficiency/abnormal blood clotting, massive hemoptysis/aortic aneurysm risk of rupture, etc.) Patients undergoing other clinical trials Estimated survival time <24h