Although acute kidney injury (AKI) frequently complicates cardiac surgery, methods to determine AKI risk in patients without underlying kidney disease are lacking. Renal functional reserve (RFR) can be used to measure the capacity of the kidney to increase glomerular filtration rate under conditions of physiological stress and may serve as a functional marker that assesses susceptibility to injury.~The investigators seek to determine whether a reduced preoperative RFR predicts postoperative AKI in patients with normal estimated glomerular filtration rates undergoing elective cardiac surgery. All centres will measure RFR with creatinine clearance, except University Hospital Giessen where in addition iohexol plasma-clearance will be used.
The investigators seek to determine whether a reduced preoperative renal functional reserve predicts postoperative acute kidney injury in patients with normal estimated glomerular filtration rates undergoing elective cardiac surgery.