Overview

Renal complications are frequently encountered in cardiac surgery and constitute significant causes of morbidity and mortality. They most commonly present in the form of acute kidney injury (AKI). The etiological factors of AKI include hemodynamic alterations, hemolysis and pigment nephropathy, inflammatory response and cytokine storm, ischemia-reperfusion injury, use of nephrotoxic agents, patient-related risk factors (advanced age, diabetes mellitus, preoperative renal insufficiency, congestive heart failure, hypertension, anemia), duration of surgery, and postoperative complications such as low cardiac output syndrome, sepsis, bleeding and reoperation, hypoalbuminemia, and fluid imbalance.

Previous studies have demonstrated several mechanisms through which elevated HbA1c levels may contribute to acute renal injury, including glomerular damage and hyperfiltration, endothelial dysfunction and microvascular injury, tubular damage, accumulation of glycation products and advanced glycation end products (AGEs), structural changes in blood vessels, and metabolic and systemic factors.

The evaluation of acute renal failure relies on fundamental scoring systems, biomarkers, and imaging modalities. Among the scoring systems, the most current and widely used is the KDIGO (Kidney Disease: Improving Global Outcomes) classification. According to the KDIGO definition, the diagnosis of AKI can be established when at least one of the following three criteria is met: an increase in serum creatinine of ≥0.3 mg/dL within 48 hours, an increase in serum creatinine to ≥1.5 times baseline within 7 days, or a urine output of \<0.5 mL/kg/hour for more than 6 hours. AKI staging is performed based on these parameters.

Imaging modalities used in the assessment of renal function include renal ultrasonography (US), Doppler ultrasonography with measurement of the renal resistive index (RRI), renal MRI/MR angiography, and renal computed tomography (particularly CT angiography). RRI is a non-invasive, bedside-applicable method that provides direct information about renal vascular resistance by evaluating renal arterial flow patterns.

In our clinic, the rationale of the present study is to measure preoperative HbA1c and Doppler-derived RRI values in patients undergoing isolated coronary artery bypass surgery, and to evaluate their relationship with postoperative KDIGO classification and Doppler RRI values in order to gain insight into the development of AKI.

Eligibility

Inclusion Criteria:

• Patients undergoing isolated elective CABG surgery
• Patients with available preoperative and postoperative Doppler RRI measurements
• Patients with available HbA1c data

Exclusion Criteria:

• Patients with chronic kidney disease
• Emergency surgeries
• Redo/revision surgeries
• Patients undergoing concomitant valve surgery
• Presence of acute infection or sepsis
• Advanced heart failure (EF \<30%)
• Requirement for intra-aortic balloon pump, pacemaker, or mechanical circulatory support
• History of nephrectomy or single kidney
• Preoperative serum creatinine \>2.0 mg/dL
• Pregnancy
• Refusal to participate in the study