<prompt> A 65-year-old man has urine output of 10 mLh following abdominal aortic aneurysmectomy. Acute tubular necrosis is suggested by the presence of which of the following?Urine osmolality of more than 500 mOsmkgUrine sodium of more than 40 mEqLFractional excretion of sodium of 1Blood urea nitrogen BUN-to-serum creatinine ratio SCR of more than 20  <response>: Oliguria may be prerenal or renal. The following table characterizes findings in prerenal failure versus those observed in intrinsic renal failure acute tubular necrosis.PRERENAL VS. INTRINSIC RENAL FAILURE Prerenal FailuresIntrinsic Renal FailuresUrine osmolality mOsmkg500350Urine sodium mEqL2040Fractional excretion of sodium12BUNSCR2010UrinePCR4020 