Table 2. Grading standards of postoperative complication (23).

Grade	Description
I	Without any intervention
II	Only drug intervention
IIIA	Need not under the general anesthesia further intervention
IIIB	Need further intervention under general anesthesia
IVA	Need a single organ life support
IVB	Need multiple organ support life
V	Death due to the complications

Level I pulmonary complications: prolonged gas leakage; Level II and above pulmonary complications: other postoperative pulmonary complications except prolonged air leakage, including pulmonary infection, atelectasis, acute lung injury, and asthma, are collectively referred to as level II and above pulmonary complications.