Acute kidney injury (AKI) is a common and serious complication following cardiac surgery performed under cardiopulmonary bypass and is associated with increased morbidity, mortality, and prolonged hospital stay. Despite advances in perioperative management, the ability to accurately predict postoperative AKI remains limited.

Recent evidence suggests that preoperative inflammatory markers derived from routine laboratory tests, as well as indicators of intraoperative perfusion stress, may play an important role in the development of AKI. However, data evaluating these factors together in patients undergoing cardiac surgery with cardiopulmonary bypass are limited.

This retrospective observational cohort study aims to investigate the association between preoperative renal function, inflammatory indices, and intraoperative perfusion-related parameters with the development of postoperative AKI. Acute kidney injury will be defined according to the KDIGO serum creatinine criteria within the first 72 hours after surgery. The findings of this study may help identify patients at increased risk for AKI and contribute to improved perioperative risk stratification in cardiac surgery.

Acute kidney injury (AKI) is a frequent complication after cardiac surgery performed under cardiopulmonary bypass (CPB) and represents a major determinant of short- and long-term adverse outcomes. The pathophysiology of postoperative AKI is multifactorial and involves hemodilution, non-pulsatile flow, ischemia-reperfusion injury, systemic inflammatory response, and alterations in renal perfusion during CPB. Despite similar surgical and anesthetic management, not all patients develop AKI, suggesting that preoperative patient-related factors and intraoperative perfusion stress play a critical role.

In recent years, easily accessible inflammatory indices derived from routine hematological and biochemical parameters, such as the neutrophil-to-lymphocyte ratio, systemic immune-inflammation index, and C-reactive protein to albumin ratio, have been proposed as potential predictors of postoperative complications, including AKI. In addition, intraoperative parameters reflecting perfusion stress, such as cardiopulmonary bypass duration, arterial lactate levels, and acid-base disturbances, may further contribute to renal injury. However, studies evaluating these factors together in the setting of cardiac surgery with CPB are limited.

This single-center, retrospective observational cohort study will include adult patients who underwent cardiac surgery under cardiopulmonary bypass. Demographic data, comorbidities, preoperative laboratory parameters, echocardiographic findings, and intraoperative CPB-related variables will be collected retrospectively from institutional medical records. Acute kidney injury will be defined and staged according to the KDIGO serum creatinine criteria within 48-72 hours after surgery. Urine output criteria will not be evaluated due to limitations inherent to retrospective data collection.

The primary objective of the study is to identify independent predictors of postoperative AKI by assessing the combined effects of preoperative renal function, inflammatory markers, and intraoperative perfusion stress parameters. Secondary objectives include evaluation of AKI severity and in-hospital mortality. Multivariable logistic regression and receiver operating characteristic analyses will be used to determine the predictive value of selected parameters.

By improving understanding of the factors associated with postoperative AKI, this study aims to support better perioperative risk stratification and inform future prospective investigations in patients undergoing cardiac surgery with cardiopulmonary bypass.

Inclusion Criteria:

• Adults aged 18 years or older
• Patients who underwent cardiac surgery under cardiopulmonary bypass
• Coronary artery bypass grafting, valve surgery, or combined cardiac surgery
• Elective or emergency procedures

Exclusion Criteria:

• Preoperative end-stage renal disease requiring dialysis
• Preoperative serum creatinine level greater than 4.0 mg/dL
• Off-pump cardiac surgery
• Missing preoperative or postoperative serum creatinine data

Adult patients undergoing cardiac surgery with cardiopulmonary bypass at a single tertiary care center.

Individual participant data will not be shared due to the retrospective nature of the study and institutional data protection and patient confidentiality regulations. Only de-identified aggregate data will be reported in publications.