Inclusion Criteria:  Inclusion Criteria:  18 to 80 years of age Meet the diagnostic criteria Receive invasive mechanical ventilation within 48 hours  -  Exclusion Criteria:  Patients with those disease will be excluded ： chronic obstructive pulmonary disease Pulmonary embolism Chronic heart failure Idiopathic pulmonary fibrosis Pulmonary hypertension Pregnant women will be excluded too.  -