Postoperative pulmonary complications (PPCs) occur in many patients, especially those with high risks, and are associated with increased hospital length of stay, morbidity and costs of care. According to European Perioperative Clinical Outcome definitions, major pulmonary complications include atelectasis, respiratory infection, pleural effusion, and pneumothorax. Because identifying patients at high risk for PPCs may allow earlier treatment, predictive scores ( the Assess Respiratory Risk in Surgical Patients in Catalonia score [ARISCAT]) have been developed.Lung ultrasound (LUS) is more accurate than chest X-ray in diagnosing pulmonary complications, and lung ultrasound performed in the postanesthesia care unit may identify patients at higher risk for pulmonary complications. So we aimed to study if lung ultrasound can guide the prevention of PPCs in moderate to high risk patients.

patients recruited are randomized into the two groups: LUS group and Control group. Patients in LUS group received ultrasound examination and guided the treatment according to the ultrasound results, while the control group did not receive ultrasound examination, just the same as the routine clinical practice. This study aims to explore whether ultrasound-guided clinical treatment can reduce the incidence of postoperative pulmonary complications in moderate to highrisk patients. Before operation, informed consent was signed according to the inclusion criteria, and the incidence of pulmonary complications within 5 days after operation (or before discharge) was recorded after operation.

Inclusion Criteria:

• Age≥18 Estimated ARISCAT score ≥26分

Exclusion Criteria:

• transferred to ward or ICU directly day surgery (patients won't stay in hospital longer than 24 hours after surgery actual ARISCAT score < 26分 the technical incompatibility of the acoustic window patients refused pregnant