INTRODUCTION: Postoperative acute kidney injury (AKI) is a common postoperative complication in cardiac surgery, with varying reported incidences and prognostic factors. Renal hypoperfusion is believed to be a key factor contributing to postoperative AKI. Near-infrared spectroscopy (NIRS) monitoring, which assesses regional tissue saturation (RSO METHODS AND RESULTS: After a systematic search in PubMed, EMBASE, and Cochrane library, twenty studies (1517 patients) were included. The inter-rater agreement on study quality was strong, yet a high risk of bias was identified. CONCLUSION: The heterogeneity of the results-in part attributable to several potential confounding factors regarding study population, monitoring technique and the definition of AKI-together with the lack of a clear and consistent association between RSO