Acute kidney injury (AKI) is a common complication of cardiac surgery, which seriously affects the postoperative complication rate and mortality of patients.Acute kidney injury occurs in 5-30% of patients after cardiac surgery, but severe acute kidney injury requiring dialysis is relatively rare.At present, the diagnosis of AKI is based on serum creatinine (Scr) or urine volume. However, the changes of serum creatinine value have hysteresis, and the increase of serum creatinine level lags behind kidney injury for 48 ~ 72 h.Some drugs can also affect creatinine levels.Urine volume is also affected by many factors.Due to the lack of sensitivity and specificity of SCr, it is very important to find and adopt new early AKI markers.Kidney is an important metabolic organ of human body. Different from cerebrovascular system, kidney lacks automatic regulation ability and is easily affected by perfusion flow.Previous experiments have shown that placing a multi-plane esophageal probe into the human stomach through the esophagus can monitor the changes of left renal blood flow before, during and after cardiovascular surgery extracorporeal circulation, and has good repeatability, which may become an effective means to monitor renal blood flow during cardiovascular surgery.

In conclusion, this study intends to use esophageal ultrasound as a means to monitor renal blood flow, observe the changes of intraoperative renal hemodynamic indexes, and use KDIGO ( Kidney Disease:Improving Global Outcomes)as the standard of renal injury to explore the correlation between intraoperative hemodynamic changes and postoperative AKI, providing a new perspective for the pathophysiological study of AKI after cardiopulmonary bypass.

The mechanism of acute kidney injury after CPB has not been fully elucidated, and current studies suggest that the main mechanisms are as follows:

(1) endogenous/exogenous nephrotoxic substances;(2) metabolic factors: mainly reflected in the preoperative status of patients, such as obesity, low body weight, etc.;(3) hemodynamic factors: hemodynamic instability is an important mechanism for further renal injury process such as ischemia reperfusion, which is mainly reflected in: a.preoperative and postoperative hypotension: cardiogenic shock caused by cardiac insufficiency and low cardiac displacement;Non-cardiogenic shock (vasoactive drugs/allergies/postoperative bleeding);b. hemodynamic instability of intraoperative intervention: deep anesthesia, intraoperative blood loss, CPB-related intraoperative low perfusion (long CPB time, low circulation flow, low mean arterial pressure in CPB), embolic release (atherosclerotic emboli/air emboli), aorta and distal arteriotomy;(4) neurohumoral system factors: hormones such as epinephrine, norepinephrine, renin and thyroxine change to varying degrees during cardiac surgery and CPB, thus affecting the body state and systemic blood vessels;(5) inflammation and oxidative stress.

Kidney is an important metabolic organ of human body. Different from cerebrovascular system, kidney lacks automatic regulation ability and is easily affected by perfusion flow.For patients at high risk of postoperative acute kidney injury, appropriate intraoperative perfusion may reduce the incidence of postoperative acute kidney injury.

Esophageal ultrasound was used as a means of monitoring renal blood flow to observe the changes in intraoperative renal hemodynamic indexes. Meanwhile, KDIGO was used as the standard for renal injury. AKI was divided into two groups according to whether postoperative AKI occurred, and the correlation between intraoperative hemodynamic changes and postoperative AKI in the two groups was discussed.It provides new ideas for the early diagnosis of postoperative acute kidney injury.

Inclusion Criteria:

• Aged between 18 and 70;
• Elective cardiopulmonary bypass for patients undergoing cardiac surgery

Exclusion Criteria:

• Acute myocardial infarction surgery within 7 days
• Emergency surgery
• Known renal artery stenosis, renal malformation;Renal failure
• Congenital esophageal malformation
• Patients with previous history of stomach and esophagus should avoid intraoperative esophageal ultrasound examination
• Existing acute kidney injury, kidney transplantation, chronic kidney disease and glomerular filtration rate less than 30 ml/min,
• Pregnancy

60 patients undergoing elective cardiac surgery in the Affiliated Hospital of Xuzhou Medical University.

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