Development and Validation of a Risk Prediction Model for Cardiac Surgery-associated Acute Kidney Injury Based on the Gut-Kidney Axis, Incorporating Gut Microbiota and Their Metabolites

This is a single-center prospective observational cohort study enrolling adult patients scheduled for cardiac surgery. Multi-timepoint clinical indicators, stool samples for gut microbiota and metabolomics profiling and artery blood will be collected before and after surgery. We aim to construct and validate a multi-dimensional preoperative predictive model for CSA-AKI based on clinical, microbial and metabolic signatures. Meanwhile, this research will explore the potential mediating role of the gut-kidney axis in the pathogenesis of cardiac surgery-associated acute kidney injury, and provide novel mechanistic evidence for early risk stratification and intervention of CSA-AKI.

Inclusion Criteria: 1. Aged 18 years or older; 2. Scheduled for elective cardiac surgery; 3. Surgery performed under cardiopulmonary bypass (CPB); 4. Able to complete preoperative stool and blood sample collection independently; 5. The patient and their family members voluntarily participate in this study, agree to the collection of preoperative stool samples, blood samples and clinical data, cooperate with follow-up visits, and sign the informed consent form.- Exclusion Criteria: （1) Patients with end-stage renal disease or dependence on renal replacement therapy before surgery; (2) Patients with a preoperative estimated glomerular filtration rate (eGFR) \< 30 ml/min/1.73m² or severe chronic kidney disease (CKD stage 4-5); (3) Patients with a history of renal transplantation or unilateral nephrectomy; (4) Patients who received antibiotic treatment within 4 weeks before surgery; (5) Patients who took probiotic or prebiotic preparations within 4 weeks before surgery; (6) Patients with a previous history of intestinal surgery, such as colectomy and small bowel resection; (7) Patients with active inflammatory bowel disease, chronic diarrhea or constipation requiring pharmacological intervention; (8) Patients with preoperative intestinal obstruction, gastrointestinal bleeding, or those requiring fasting for more than 24 hours; (9) Patients undergoing emergency surgery (time from admission to surgery \< 24 hours), or those unable to complete preoperative informed consent, dietary investigation and baseline sample collection; (10) Patients who received mechanical bowel preparation (e.g., enema) within 24 hours before surgery; (11) Patients with preoperative active infection or sepsis; (12) Patients treated with preoperative glucocorticoids or immunosuppressants (excluding routine doses); (13) Patients who died intraoperatively or within 24 hours postoperatively, or those who could not complete the evaluation of the primary outcome (postoperative 7-day acute kidney injury \[AKI\]); (14) Female patients who are pregnant, lactating or in menstruation; (15) Patients complicated with gastrointestinal malignant tumors or receiving systemic chemotherapy, targeted therapy or abdominal radiotherapy; (16) Patients with severe liver disease (Child-Pugh grade B or above).