What is the most common cause of postoperative renal failure?

Postoperative renal failure presents with oliguria (< 500 mL/day) with rising blood urea nitrogen and creatinine. The patients at greatest risk for postoperative renal failure have baseline renal impairment. The most likely causes of postoperative renal failure are hypovolemia which causes decreased renal perfusion and acute tubular necrosis caused by transient hypotension or nephrotoxic agents. Ref: Cooper Z., Rogers, Jr. S.O. (2012). Chapter 139. Surgical Critical Care. In G.V. Lawry, S.C. McKean, J. Matloff, J.J. Ross, D.D. Dressler, D.J. Brotman, J.S. Ginsberg (Eds), Principles and Practice of Hospital Medicine.