Application of CLCVP Technique in Early Intervention of CSA-AKI

The goal of this clinical trial is to learn about in postoperative acute kidney injury in cardiac surgery. The main questions it aims to answer are: 1. Controlled low central venous pressure (CLCVP) technique can reduce the occurrence of cardiac surgery-associated acute kidney injury (CSA-AKI) by reducing venous congestion and increasing renal perfusion pressure. 2. CLCVP technique does not increase the risk of postoperative cognitive dysfunction (POCD) during cardiac surgery. Participants who are assigned to the intervention group will receive CLCVP technique. Specific methods are as follows: First,20min after the end of cardiopulmonary bypass, on the basis of ensuring that the mean arterial pressure (MAP) ≥ 60mmHg, the patients will accept dorsal elevated position. After that, if the patient's central venous pressure (CVP) is less than 10mmHg, nitroglycerin will be pumped at 0.2ug/ (kg \* min). If the patient's CVP is still greater than or equal 10mmHg, we increase the dose by 0.2ug/ (kg \* min) and pump again for 5min, and the like. Until the patient's CVP is less than 10mmHg or the dose of nitroglycerin increases to 1ug/ (kg \* min), the current dose is maintained until the end of surgery. If participants are assigned to the control group, no intervention measures will be taken. The researchers will compare the intervention group with the control group to see the occurrence of CSA-AKI and POCD after cardiac surgery.