INTRODUCTION

Acute renal failure (ARF) is an abrupt decline in filtration and excretory function of the kidney, leading to retention of uremic toxins and dysregulation of fluid, electrolyte, and acid-base balance. Although anuria and oliguria are classic features of ARF, nonoliguric and polyuric ARF are common and carry a better prognosis.

ETIOLOGY

ARF can be categorized into prerenal, intrinsic renal parenchymal, and postrenal causes. Prerenal causes include decreases in renal blood flow or perfusion or excessive vasoconstriction. Prerenal azotemia rapidly reverses when the inciting cause is eliminated. Intrinsic renal parenchymal causes include prolonged hemodynamic or ischemic events (extension of prerenal causes), infectious diseases, toxins, or systemic diseases with renal manifestations. Box 135-1 lists substances with a nephrotoxic potential. Postrenal failure is due to obstruction or diversion of urine flow, including urethral obstruction, bilateral ureteral obstruction or unilateral obstruction with a nonfunctional contralateral kidney, or urine leakage. Restoration of urine flow rapidly resolves azotemia, although prolonged obstruction may lead to intrinsic parenchymal renal failure. Calcium oxalate nephroliths and ureteroliths are encountered in cats with increasing frequency. This condition commonly has many features of ARF, although there is frequently a significant component of chronic renal damage.¹

PATHOPHYSIOLOGY

ARF proceeds through four phases. The initiation phase is the period of renal injury. Intervention at this phase may prevent progression to more severe injury, but changes in glomerular filtration rate (GFR) and urine specific gravity are not apparent at this stage. During the extension phase, cellular injury progresses to cell death. The maintenance phase occurs when irreversible renal damage has occurred. Removal of the initiating cause at this stage does not alter the existing damage. The recovery phase may last weeks to months.²

CLINICAL PRESENTATION

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