Coronary artery bypass grafting is a commonly performed heart surgery, but patients may have different risks for postoperative complications even when their preoperative risk scores are similar. EuroSCORE II is widely used to estimate surgical risk before cardiac surgery, but it may not fully reflect how the body responds during the early postoperative period.

This retrospective observational study will evaluate adult patients who underwent elective coronary artery bypass grafting with cardiopulmonary bypass between January 1, 2022 and December 31, 2025. The study will use existing hospital records and laboratory data. No additional treatment, test, or intervention will be given to patients as part of this study.

The main aim is to examine whether early postoperative changes in inflammatory and renal laboratory markers can identify different patient subgroups, called phenotypes. These markers include neutrophil-to-lymphocyte ratio, systemic immune-inflammation index, triglyceride-glucose index, and serum creatinine. The study will evaluate whether these phenotype groups are associated with postoperative acute kidney injury and prolonged intensive care unit stay.

The study will also assess whether this early postoperative phenotype-based classification provides additional risk information beyond EuroSCORE II.

This is a single-center retrospective observational cohort study designed to evaluate the prognostic relevance of early postoperative trajectory-based biological phenotyping in adult patients undergoing elective coronary artery bypass grafting with cardiopulmonary bypass.

The study population will include patients operated between January 1, 2022 and December 31, 2025. Data will be obtained retrospectively from hospital information systems, electronic medical records, laboratory databases, and archived patient files. All data will be anonymized before analysis, and no patient-identifying information will be included in the study dataset.

The study will collect demographic characteristics, comorbidities, preoperative clinical variables, EuroSCORE II, perioperative variables such as cardiopulmonary bypass time and aortic cross-clamp time, and laboratory parameters. Early postoperative laboratory values from postoperative day 0 and postoperative day 1 will be used to calculate inflammatory and metabolic indices, including neutrophil-to-lymphocyte ratio, systemic immune-inflammation index, and triglyceride-glucose index. Serum creatinine changes will be used to evaluate renal response and postoperative acute kidney injury.

Patients will be classified into phenotypic subgroups using unsupervised clustering methods based on early postoperative biomarker trajectories. The clinical characteristics and outcomes of these subgroups will then be compared. The main outcomes of interest are postoperative acute kidney injury and prolonged intensive care unit stay. Additional analyses will assess whether phenotype classification improves risk stratification beyond EuroSCORE II.

The study does not involve any intervention, experimental treatment, additional laboratory testing, or change in clinical care. All analyses will be performed using previously recorded clinical and laboratory data.

Inclusion Criteria:

• Adult patients aged 18 years or older
• Patients who underwent elective on-pump coronary artery bypass grafting
• Patients operated between January 1, 2022 and December 31, 2025
• Patients with available perioperative clinical and laboratory data required for analysis

Exclusion Criteria:

• Patients undergoing emergency surgery
• Patients undergoing concomitant valve surgery
• Patients with missing or inconsistent key clinical or laboratory data

The study population will consist of adult patients who underwent elective on-pump coronary artery bypass grafting at University of Health Sciences Bursa Yüksek İhtisas Training and Research Hospital between January 1, 2022 and December 31, 2025. Eligible patients will be identified retrospectively from electronic medical records, laboratory databases, and archived patient files.

Individual participant data will not be shared because the study uses retrospective clinical and laboratory data obtained from hospital records. Although the dataset will be anonymized before analysis, data sharing is not planned due to institutional data privacy regulations and the retrospective nature of the study.