age younger than 20 years or older than 80 years; pregnant woman; emergent cardiac surgery; use of intra-aortic balloon pump or extracorporeal membrane oxygenation after surgery, pre-existing severe renal insufficiency (defined as estimated glomerular filtration rate 15 cc/min or less by the Modification of Diet in Renal Disease study equation36); patients with end-stage renal disease under maintenance hemodialysis, peritoneal dialysis, or receiving kidney transplantation; use of radiocontrast ≤24 h prior to the surgery; use of nephrotoxic drugs before or during the surgery