Acute kidney injury (AKI) is an infrequent but major and well - recognized complication of cardiac surgery. Recent studies demonstrated that even minimal increases in serum creatinine are associated with a rising risk of mortality, hospital length of stay, and cost. Furthermore a cut-off for baseline serum creatinine and its influence on mortality after cardiac surgery has been shown.

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.

Acute kidney injury (AKI) is an infrequent but major and well - recognized complication of cardiac surgery (1, 2). Its incidence ranges from 1 to 30% (3). Numerous pre-, intra-, and postoperative factors have been associated with the development of AKI after cardiac surgery (3-19). Most commonly used definitions are the absolute serum creatinine level, its change within one week and/or the need for dialysis in previously undialysed patients (1, 3-5, 9-11, 19-25). In patients who are older, more obese with Type 2 diabetes and hypertension, there is increasing interest in the effects of chronic kidney disease on the cardiovascular system (26). Recent studies demonstrated that even minimal increases in serum creatinine are associated with a rising risk of mortality, hospital length of stay, and cost (27, 28). The Acute Dialysis Quality Initiative Group standardized with their Risk, Injury, Failure, Loss of Kidney Function, End-Stage Kidney Disease criteria and their modifications to the Acute Kidney Injury Network criteria the definitions of AKI (19, 29, 30). Both criteria need a baseline serum creatinine value for estimation (31).

In a recent published study (32) a cut-off for baseline serum creatinine and its influence on mortality after cardiac surgery has been shown. Under the steady-state and stable kidney function, SCr is usually produced at a relatively constant rate by the body depending on the absolute amount of muscle mass, and is a reliable and cost-effective surrogate marker for kidney function (33). SCr is strongly correlated with weight, total body water and anthropometrically estimated lean body mass (LBM) (34). Approximately half of LBM is comprised of skeletal muscle mass (35). Recent studies suggest that higher muscle mass is associated with greater longevity in people with CKD and other chronic disease states (36, 37). SCr, however, has several limitations, such as variations in concentration related to age, sex, muscle mass and is influenced by dietary protein intake. (38) Furthermore AKI affects different complex cellular and molecular pathways. Several novel urinary biomarkers such as insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and neutral endopeptidase (NEP) are involved in the early phase of cell injury and predict both the development and severity of AKI and renal recovery early after cardiac surgery (39-43) 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.

Inclusion Criteria:

• Elective cardiac surgical intervention

Exclusion Criteria:

• Emergency procedures
• Heart transplantation
• Elective left ventricular assist device (LVAD) implantation o Pulmonary thrombendarterectomy
• Declined informed consent
• Age < 18 years
• Pregnant woman
• Preoperative renal replacement therapy (RRT)

Patients undergoing an elective cardiac surgical intervention.