Inclusion Criteria:  All critically ill adult patients with cervical spinal cord injury who require mechanical ventilation and informed consent to be admitted to the Department of Critical Care Medicine of Peking University Third Hospital were selected by the subjects or their close relatives to enter the clinical study.  Exclusion Criteria:  previous chronic obstructive pulmonary disease, diagnosis of acute respiratory distress syndrome at admission, presence of pneumothorax at admission, subjects or close relatives who refused to participate in the study, and non-signed informed consent."