Renal Failure, Acute

– Sudden impairment of renal function marked by rapid, steadily increasing azotemia with or without oliguria.

Causes and Incidence

Acute renal failure (ARF) may be caused by (1) prerenal factors that interfere with renal perfusion (e.g., fluid and electrolyte depletion, hemorrhage, septicemia, cardiac or liver failure, heat stroke, burn-induced fluid depletion, myoglobinuria); (2) postrenal factors that cause obstruction (e.g., prostatism, calculi, tumors of the bladder or pelvis); or (3) renal factors that directly impair renal function (e.g., acute tubular injury, acute glomerulonephritis, disseminated intravascular coagulation, arterial or venous obstruction, tubulointerstitial nephritis, intrarenal precipitation). About 1% of all hospital admissions in the United States are for ARF, and the mortality rate is about 50%. ARF caused by prerenal or postrenal factors is more treatable than ARF caused by renal factors.

Disease Process

Prerenal azotemia results from inadequate renal perfusion. As the glomerular filtration rate (GFR) is reduced, sodium and water resorption is enhanced, causing oliguria. Urinary osmolarity is high, and urine sodium concentrations are low. Four mechanisms may be at work, either independently or in concert, in ARF caused by renal factors: (1) a decrease in renal blood flow; (2) a reduction in glomerular permeability; (3) tubular obstruction; and (4) diffusion of glomerular filtrate across injured tubular epithelium. Other mechanisms are unclear at present. Postrenal azotemia results from obstruction and subsequent glomerular or tubular dysfunction and mimics renally caused ARF in manifestation.

Symptoms

Prerenal
Nausea, vomiting, diarrhea, decreased tissue turgor, dry mucous membranes, bad taste in the mouth, oliguria, somnolence, fatigue, hypotension, tachycardia

Renal
Nocturia, fatigue, decreased mental acuity, fever, skin rash, edema, headache, anorexia, nausea, vomiting, oliguria or anuria, weight gain, rales, hypertension

Postrenal
Renal signs plus difficulty voiding, changes in urine flow, possibly flank pain

Potential Complications

ARF can lead to renal shutdown, which affects all other body systems and if left untreated leads to death. Even with treatment, pulmonary edema, hypertensive crisis, acidosis, hyperkalemia, and infection are common, and death occurs in as many as 50% of all diagnosed cases.

Diagnostic Tests

Diagnosis is directed to classification of the condition as prerenal, renal, or postrenal.

Urine
Prerenal: decreased pH, urine sodium, oliguria; increased specific gravity; normal creatinine and sediment Renal: decreased specific gravity; increased urine sodium and creatinine; oliguria or normal volume; sediment contains casts, pyuria Postrenal: normal specific gravity, urine sodium, and creatinine; sediment normal or hematuria possible

Serum
Decreased pH, calcium, bicarbonate; increased potassium, chloride, phosphate, blood urea nitrogen, creatinine, osmolality; sodium normal or decreased; hemoglobin and hematocrit elevated with dehydration and decreased with hypervolemia; decreased adhesiveness of platelets

Ultrasound/computed tomography scan
Kidneys may be enlarged

Renal scan/IV urogram
To visualize obstructions, tumors, and masses

Treatments

Surgery
Renal transplantation when cause is renal and unresponsive to other treatment.

Drugs
Alkalinizing agents for acidosis; potassium-removing resins for hyperkalemia; vasodilators, angiotension antagonists, or calcium antagonists to treat hypertension; diuretics in prerenal disease to increase perfusion unless oliguria is present; dopamine if vasopressor is needed; antiinfective drugs for associated infections (only antibiotics excreted primarily by the liver are used).

General
Limitation of all drugs that require renal excretion; balance of fluid intake and output (IoO), avoiding fluid overload; highcarbohydrate, low-protein feedings, essential amino acid replacement by IV and at least 100 g of glucose per day; decreased potassium and sodium intake if levels are elevated; vitamin supplements; careful management of skin care to reduce dryness and prevent injury or infection; careful monitoring of IoO, weight, electrolytes, vital signs, cardiac status, and mental status; peritoneal or hemodialysis the treatment of choice when milder measures fail; information about dietary and fluid restrictions, medications, and dialysis.