Kidney Oxygen Saturation and NGAL for Detecting Acute Kidney Injury After Cardiac Surgery

This prospective, single-center observational study was conducted at Haseki Training and Research Hospital, Istanbul, Türkiye, between March 20, 2025, and February 20, 2026. The study received ethics committee approval on March 19, 2025 (approval number: 34-2025), and written informed consent was obtained from all participants.

Among 95 adult patients assessed for eligibility, 85 patients undergoing elective cardiac surgery with cardiopulmonary bypass (CPB) were enrolled.

Renal regional oxygen saturation (rSO₂) was monitored using bilateral near-infrared spectroscopy (NIRS) probes placed over the renal regions. Perioperative measurements were collected during four predefined phases:

A0: Before induction of anesthesia.

A1: From induction of anesthesia to initiation of CPB.

A2: From initiation of CPB to separation from CPB.

A3: From separation from CPB to the end of surgery.

During A1, A2, and A3, right and left renal rSO₂ values and other perioperative parameters were recorded every 15 minutes. Mean values were calculated separately for each phase. Bilateral mean renal rSO₂ was calculated as the arithmetic mean of the corresponding right- and left-sided values and was used as the primary renal oxygenation parameter.

Urine output was recorded for each perioperative phase and expressed as mL/kg/h.

NGAL levels were measured preoperatively (T0) and at 24 (T24) and 48 (T48) hours postoperatively.

Postoperative AKI was assessed during the first seven postoperative days according to KDIGO criteria using serum creatinine changes and/or urine output.

Participants were classified into AKI and non-AKI groups according to postoperative AKI development.

The diagnostic performance of renal rSO₂ and NGAL was assessed using receiver operating characteristic (ROC) curve analysis. The primary combined biomarker model incorporated bilateral mean renal rSO₂ during CPB (A2) and NGAL measured at 24 hours postoperatively (T24).

Additional analyses investigated temporal changes in biomarkers and potential patient-related and perioperative factors associated with postoperative AKI.

Inclusion criteria

• Age ≥18 years.
• Scheduled for elective cardiac surgery with cardiopulmonary bypass.
• Expected postoperative coronary intensive care unit stay of at least 48 hours.
• Written informed consent provided.

Exclusion criteria

• Previously diagnosed renal disease, including acute tubular necrosis, chronic kidney disease, or nephropathy.
• Use of medications known to affect renal function, including nonsteroidal anti-inflammatory drugs (NSAIDs).
• History of renal surgery or kidney transplantation.
• Skin-to-kidney depth ≥4 cm.
• Emergency cardiac surgery.
• Off-pump cardiac surgery.
• Preoperative estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m².
• Intraoperative conditions requiring a reduction in cardiopulmonary bypass pump flow with mean arterial pressure below 50 mmHg.