Transbronchial Lung Cryobiopsy in Undiagnosed Acute Respiratory Failure

Inclusion Criteria: 1. Diagnosis of acute hypoxemic respiratory failure 2. Routine assessments \[including bronchoscopy, bronchoalveolar lavage fluid cytology and pathogenic (including pathogenic mNGS) tests, blood tests, etc.\] do not clarify the etiology, or there is an unexplained disease process 3. Imaging shows a multi-lobar segmental distribution of ground glass opacity with or without consolidations 4. Patients' families agreed to participate in the study and signed an informed consent form Exclusion Criteria: 1. Significant hemodynamic instability 2. Uncorrectable coagulopathy 3. Severe pulmonary hypertension 4. Acute coronary syndrome 5. Intermediate-high-risk acute pulmonary embolism 6. Acute phase of stroke 7. Severe emphysema 8. Aortic dissection and massive gastrointestinal bleeding 9. Other conditions that are not suitable for participation in the clinical trial