In this study the investigators want to test if increased bSCr is influenced by body composition. Further the investigators want to determine if the incidence of AKI is different in patients below or above the estimated cut-off. Therefore the investigators want to perform a prospective cohort analysis and will take several other body composition and nutrition parameters to test their influence on the predictive power of bSCr. Furthermore the investigators want to evaluate several novel biomarkers for AKI on their predictive effect in cardiac surgical patients.