The investigators see a relatively high incidence of postoperative acute kidney injury (AKI) following aortic surgery. Neutrophil Gelatinase Associated Lipocalcin (NGAL) may be useful in the early diagnosis of postopeative AKI. However, NGAL is also known as a marker of inflammatory activation. The ischaemia-reperfusion injury and subsequent inflammatory response to aortic cross clamping may per se induce a rise in NGAL despite intact renal function. Therefore NGAL may not be a reliable marker of AKI after AAS.