Pathophysiology of Acute Renal Failure

Abstract

Acute renal failure is a clinical syndrome of diverse etiology characterized by a marked and rapid reduction in glomerular filtration rate (GFR), which impairs the ability of the kidneys to maintain the composition of body fluids. GFR falls from the normal values of 100–140 ml/min to 1–10 ml/min. Classically, the decrement in renal function is associated with a marked reduction in GFR to less than 5 ml/min and a fall in urine output to less than 500 ml/24 hr (oliguria). It is being increasingly recognized, however, that acute renal failure may occur without such severe reductions in GFR (usually to levels of 5–10 ml/min) and under these conditions urine output may be greater than 500 ml/day giving rise to the term nonoliguric acute renal failure. The definition of oliguria (<500 ml/24 hr) arises from the fact that this approximates the minimum volume of urine required to excrete the 600 mOsm of solute generated from normal diet and metabolism under conditions of maximal urine osmolality which seldom exceeds 1200 mOsm/kg water in man. The term anuria, which literally means “no urine output,” is often applied to urine volumes of less than 100 ml/24 hr.