Renal Near-Infrared Spectroscopy Monitoring and Postoperative Acute Kidney Injury in Cardiac Surgery

Acute kidney injury (AKI) is one of the most common complications following cardiac surgery performed with cardiopulmonary bypass and is associated with increased morbidity, prolonged intensive care unit stay, and higher mortality rates. Early detection of renal hypoperfusion during surgery may allow timely interventions to prevent postoperative kidney injury. Near-infrared spectroscopy (NIRS) provides non-invasive and continuous monitoring of regional tissue oxygen saturation and may be useful for detecting renal tissue hypoxia during cardiac surgery.

The aim of this prospective observational study is to investigate the effectiveness of intraoperative renal NIRS monitoring in predicting postoperative acute kidney injury in patients undergoing elective cardiac surgery with cardiopulmonary bypass.

The study will be conducted in the operating rooms of Istanbul Prof. Dr. Cemil Tascioglu City Hospital. A total of 115 adult patients scheduled for elective coronary artery bypass graft surgery or heart valve repair or replacement with the use of cardiopulmonary bypass will be included. Patients younger than 18 years, those with a body mass index greater than 35 kg/m², preoperative renal dysfunction, preoperative inotropic support, mechanical ventilation requirement, acute coronary syndrome requiring urgent intervention, or acute aortic dissection will be excluded from the study.

Before surgery, demographic data including age, sex, body mass index, comorbidities, previous surgeries, ejection fraction, and current medications will be recorded. Laboratory parameters including hemoglobin, creatinine, glomerular filtration rate, bilirubin levels, and lactate dehydrogenase will also be collected. Risk scores including ASA classification, Charlson Comorbidity Index, and EuroSCORE II will be calculated.

Renal and cerebral tissue oxygen saturation will be continuously monitored intraoperatively using a near-infrared spectroscopy device (Masimo Root® with O3® Regional Oximetry). Sensors will be placed over the renal regions determined by ultrasonographic localization before surgery. Hemodynamic parameters, arterial blood gas values, and intraoperative variables will be recorded at predefined time points during anesthesia induction, cardiopulmonary bypass, and after separation from cardiopulmonary bypass.

All patients will receive standard anesthesia management and cardiopulmonary bypass procedures according to institutional protocols. Urine output, cardiopulmonary bypass duration, total operation time, intraoperative blood transfusion, use of diuretics, and ultrafiltration will also be recorded.

Postoperative renal function will be evaluated by measuring serum creatinine levels and urine output. Patients will be followed in the cardiovascular intensive care unit, and laboratory parameters including creatinine and estimated glomerular filtration rate will be recorded for seven days after surgery.

Acute kidney injury will be defined according to the Kidney Disease Improving Global Outcomes (KDIGO) criteria. Patients will be classified into two groups according to the presence or absence of postoperative acute kidney injury, and the relationship between intraoperative renal NIRS measurements and the development of AKI will be analyzed.