《内科学精品教学课件-同济》35acute renal failure2012.pptVIP

* Multiple serum and urinary laboratory values or indices can help physicians distinguish among prerenal, renal, and postrenal causes of AKI (Figure 3). The fraction of filtered sodium (FeNa) that is excreted in the urine serves as a useful tool in assessing the tubular integrity of a functioning nephron, primarily in an oliguric state. A FeNa (urine sodium plasma creatinine plasma sodium urine creatinine) level of less than 1% has a diagnostic accuracy of approximately 80% for prerenal azotemia.18 Other conditions associated with FeNa levels of less than 1% include sodiumavid states (eg, congestive heart failure, cirrhosis, nephrosis), contrast-induced nephropathy, rhabdomyolysis, and severe glomerulonephritis (glomerular nephritis). In addition, a patient’s FeNa level may be misleading (ie, inappropriately elevated) in the setting of CKD, diuretic use, and glycosuria. The calculated fractional excretion of urea (FeUrea) can function as a surrogate for FeNa when patients have received diuretic therapy. An FeUrea level of less than 35% suggests prerenal etiology. A urine osmolality higher than 500 mOsm/L, a blood urea nitrogen to creatinine ratio greater than 20 to 1, urine sodium less than 20 mEq/L, and bland urine sediment all support a diagnosis of prerenal azotemia. Conversely, a urine osmolality of less than 400 mOsm/L, high urine sodium (ie, 40 mEq/L), and urine sediment with muddy brown or granular casts suggests tubular injury. Renal ultrasonography aids in ruling out postrenal etiology of AKI. * The third leading cause of AKI in the hospital setting, this condition is defined by an increase in serum creatinine levels that is 25% or higher (0.5 mg/dL) within 72 hours of contrast media administration. Given the escalating number of procedures and diagnostic studies that require the use of contrast media, a larger percentage of the population is now at risk of CIN. Associated risk factors for CIN include older age, diabetes, underlying chronic CKD, multiple m