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ETIOLOGY, PATHOGENESIS AND CLASSIFICATION OF ACUTE RENAL FAILURE

Acute renal failure (ARF, acute tubulopathy) is a number of specific changes in the structure of renal tissue, expressed in dystrophy and necrosis of the epithelium of renal tubules as a reaction to the endogenic or exogenic factor of aggression, the result of which is acute disturbance of renal functions with severe clinical manifestations, disbalance of water and electrolytes, retention of products of nitrogen metabolism and other disorders of homeostasis.

Etiologically 3 forms of ARF are distinguished:

1. Prerenal.

2. Renal (intrarenal).

3. Postrenal.

Prerenal ARF arises, chiefly, as a consequence of shock disorder of blood circulation (hemorrhagic, traumatic, septic, burn, toxic and other etiologic varieties of shock) with disturbance of renal blood flow by the type of Truet's shunt (ischemia of cortical layer and overfilling with blood of medullary layer) and development of the "shock kidney". To prerenal ARF we also refer ARF, arising in hemolysis and myolysis, when the occlusion of tubules occurs with acidic hematin and myoglobin crystals (acute poisoning with hemolytic poison, transfusion of incompatible blood, crush syndrome, nontraumatic muscular ischemia, electric injury, burns, absorption of hypotonic solutions), in significant loss of electrolytes and dehydration (persistent vomiting, diarrhea, burns, prolonged application of diuretics, dehydration as a result of operation), endogenic intoxications (ileus, peritonitis, hepatorenal syndrome, gestational toxicosis).

Renal ARF arises as a result of direct effect of nephrotoxic poisons on tubular epithelium — "toxic kidney" (poisoning with heavy metals, carbon

tetrachloride, phosphorus, ethylene glycol, fungi, etc.); in toxico-allergic influence (sulfanilamides, antibiotics, barbiturates, colloid gold, bismuth); in infection, hemorrhagic fever, pyelonephritis, acute anuretic glomerulonephritis.

To postrenal causes we refer cases of acute disorder of the urine passage along the ureter as a result of occlusion with a concrement, tumor, stricture, inflammatory process characterizing by syndrome of anuria with changes of homeostasis typical for ARF.

In connection with the fact that the forms of ARF are varied, in its pathogenesis take part different mechanisms. Organic lesions of renal parenchyma of necrotic nature lie in the basis of ARF (both "shock kidney" and "toxic kidney"). For the most part, a tubular epithelium is affected. Here, histologic alterations of two types are observed: tubulonecrosis — with preservation of basal membrane, and tubulor-rhexis — with its complete destruction and rupture of tubules. As long as regeneration of renal epithelium is possible only if the membrane is preserved, the consequence of tubulorrhexis is cicatrization, i.e. nephrosclerosis, and restoration of tubular function at this place is impossible.

Tubulonecrosis and tubulorrhexis are united under a common term "ac ate necrotic nephrosis" (necronephrosis). A degree of ARF reversibility is determi­ned by a prevalence of that or other kind of tubules lesion. In shock a tubulorrhexis prevails, in nephrotoxic effect — tubulonecrosis. A complete necrosis of the cortical layer of both kidneys is encountered more rarely — it is a bilateral or symmetrical cortical necrosis, practically irreversible process at which the prognosis for life is extremely serious.

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