Acute kidney injury (AKI), which can occur after major surgeries, leads to increased morbidity and mortality if not detected and managed promptly. In clinical practice, serum creatinine and urine output values of patients are monitored to detect AKI, but these parameters can cause delays in diagnosis. Additionally, studies have been conducted on biomarkers such as Neutrophil Gelatinase-Associated Lipocalin (NGAL) and cystatin C in recent years, but definitive results have not been achieved.

Renal Doppler Resistive Index (RDRI) is a non-invasive index believed to reflect renal vascular perfusion. RDRI measurement is a repeatable, inexpensive, and easy-to-apply technique. RDRI has been found to be associated with AKI in conditions such as renal dysfunction, hypertension, and post-traumatic hemorrhagic shock. Furthermore, due to the impact on renal perfusion in patients undergoing major surgery, RDRI, which reflects renal vascular resistance, can serve as an indicator of kidney perfusion.

The aim of this study is to test the hypothesis, 'Does measuring postoperative RDRI in major abdominal surgery cases yield higher sensitivity and specificity values in detecting acute kidney injury compared to NGAL?'

Inclusion Criteria:

• ASA I-III,
• Patients undergoing elective major abdominal surgery

Exclusion Criteria:

• Chronic kidney failure,
• Using nephrotoxic drugs,
• Patients with a history of kidney transplantation or nephrectomy

Patients who will undergo major abdominal surgery in Antalya Training and Research Hospital.