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| AuthorsMitchell H Rosner, MDMark D Okusa, MD | Section EditorPaul M Palevsky, MD | Deputy EditorAlice M Sheridan, MD |
Topic Outline
INTRODUCTION
Patients who are hypotensive due to surgery, sepsis, bleeding, or other causes are at risk of developing postischemic (also called ischemic) acute tubular necrosis (ATN) especially if the impairment in renal perfusion is either severe or prolonged in duration. This disorder is characterized by a rising plasma creatinine concentration, a urine volume that may be reduced or normal, and a characteristic set of changes in the urinalysis, including many granular casts and a fractional excretion of sodium above 1 percent and fractional excretion of urea above 35 percent.
The pathogenesis and etiology of postischemic ATN will be reviewed here [1,2]. The diagnosis of ATN, potential therapies for postischemic ATN, and other causes of ATN are discussed separately. (See "Possible prevention and therapy of postischemic (ischemic) acute tubular necrosis" and "Etiology and diagnosis of prerenal disease and acute tubular necrosis in acute kidney injury (acute renal failure)" and "Manifestations of and risk factors for aminoglycoside nephrotoxicity" and "Clinical features and diagnosis of heme pigment-induced acute kidney injury (acute renal failure)" and "Pathogenesis, clinical features, and diagnosis of contrast-induced nephropathy".)
PATHOLOGY AND PATHOGENESIS
The process underlying ischemic ATN occurs in multiple phases, including prerenal (impairment in renal perfusion), initiation of injury, extension of injury, maintenance, and repair [3]. The major histologic changes in ATN are effacement and loss of proximal tubule brush border, patchy loss of tubule cells, focal areas of proximal tubule dilatation, distal tubule casts, and areas of cellular regeneration that appear during the phase of recovery of renal function (picture 1A-B) [4,5].
However, the decline in renal function is usually more prominent than the severity of the histologic changes. In some cases necrotic cell death is not readily apparent and is restricted to the outer medullary regions (including the S3 segment of the proximal tubule and thick ascending limb of the loop of Henle). In addition to observable tubule obstruction and cell death, other factors may contribute to the decline in glomerular filtration rate (GFR) [4,6]:
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