Postoperative pulmonary complications(PPCs) including, but not limited to ,hypoxemia, pneumonia, ventilator-induced lung injury, and acute respiratory distress syndrome (ARDS),atelectasis,pleural effusion .PPCs may result in increased resources utilization, delayed mobilization, prolonged need of supplemental oxygen or mechanical ventilation,and a longer hospital stay.postoperative pulmonary complications are common after cardiac surgery, often increasing postoperative morbidity and mortality.The extracorporeal circulation,increased oxygen concentration inhaled and the development of massive atelectasis after open-chest surgery commonly activate lung inflammation, amplifying the harm Injury of pulmonary .Currently, plenty of interventions have been studied to prevent PPCs after surgery. Most of the recent research has focused on physical therapy such as lung-protective modes during intraoperative mechanical ventilation, Alveolar Recruitment, and respiratory muscle training.These therapies have a certain effect, but still not satisfactory.Ascorbic acid is an important cofactor in multiple enzymatic reactions where its main function is as a reducing agent.Studies have shown that ascorbic acid can reduce both ischemia-reperfusion injury and oxidative stress. Unfortunately, no studies examined whether Ascorbic acid can reduce PPCs.

The possible mechanisms of ascorbic acid to alleviate ischemia-reperfusion injury are as follows: 1 Ascorbic acid as a first-line antioxidant in plasma can reduce stress by eliminating excess Reactive oxygen species and reduce damage. 2 provides rapid electron transfer to react with superoxide and hydroxyl group to scavenge reactive oxygen released into the circulation. 3 Ascorbic acid can reduce lipid peroxidation and reduce lung injury caused by ischemia-reperfusion by scavenging oxygen free radicals. 4 Vitamin C can promote the production of cytokines by immune cells to reduce local inflammatory reactions and improve tissue microcirculation.The study aims to explore whether daily used Ascorbic acid in the perioperative period has a preventive effect on PPCs in patients undergoing cardiac surgery, and through short-term and long-term follow-up, to investigate the effect on post-hospitalization Prognosis .

Inclusion Criteria:

1. Age between 18-60 years old
2. Selective cardiac surgery under cardiopulmonary bypass

Exclusion Criteria:

1. Emergency surgery
2. Previous cardiac surgery
3. Severe lung disease
4. BMI<18 or >30
5. Mean pulmonary arterial pressure >40 mmHg
6. were allergic to ascorbic acid

Individual Participant Data(IPD) will be available when this trial is finished and the article have been published