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Diagnosis and Treatment of Acute Renal Failure

• Acute kidney injury – acute renal failure: causes, pathophysiology and symptoms
• Acute kidney injury – acute renal failure: diagnosis and treatment

Review literature: (Klahr and Miller, 1998) (Lameire et al., 2005) (Schrier and Wang, 2004 ) (Thadhani et al., 1996).

Diagnosis of Acute Renal Failure

Medical History

The aim is to identify causes of acute kidney injury to enable targeted therapy: Shock? Hypovolemia? Toxins? Medication? Extrarenal symptoms of systemic diseases? Preexisting chronic kidney disease?

Urine Tests

• Urine sediment: a normal sediment indicates a prerenal, postrenal, or vascular cause of AKI. Granulocyte cylinders indicate acute tubular necrosis, erythrocyte cylinders glomerulonephritis or vasculitis; leukocytes are caused by interstitial nephritis or pyelonephrititis, and uric acid crystals may be seen in tumor lysis syndrome.
• Urine culture to identify bacteriuria
• 24-hour urine collection with measurement of creatinine, electrolytes, protein excretion, osmolality, pH.

Differential Diagnosis of Sodium Excretion in Acute Renal Failure:

Sodium excretion in the urine can distinguish between prerenal or renal causes of acute kidney injury. In tubular dysfunction, the sodium is not reabsorbed, resulting in high urinary sodium concentrations. A urinary sodium concentration of less than 10 mmol/l is typical for prerenal kidney failure.

The fractional sodium excretion (FeNa) calculates the sodium excretion in relation to the creatinine excretion; see the formula below. The concentrations of sodium in the urine and plasma (U_Na and P_Na) and creatinine in urine and plasma (U_Krea and P_Krea) are needed. A FeNa less than 1 suggests renal kidney failure, and a FeNa of >1 a prerenal kidney failure:

FeNa = (U_Na × P_Krea)/(P_Na × U_Krea)

Laboratory tests

• complete blood count
• electrolytes
• blood gas analysis
• creatinine, uric acid, urea
• LDH, CK, lipase, liver enzymes
• protein electrophoresis, albumin
• CRP
• clotting tests

Ultrasound Imaging

Ultrasound imaging determines kidney size, renal blood flow and RI. The exclusion of obstructive uropathy and urinary retention is paramount. Ultrasound imaging of the other organs is necessary to detect underlying diseases (e.g., liver diseases, ileus or ascites).

Abdominal CT

If renal ultrasound imaging is equivocal, an abdominal CT scan without contrast can rule out a postrenal kidney failure.

Renal Biopsy

Renal biopsy is indicated in acute renal failure with nephritic urine sediment: (micro)hematuria, dysmorphic red blood cells, urinary casts with red blood cells, and proteinuria.

Treatment of Acute Renal Failure

General measures

• Correction of hypotension or volume deficit.
• Review of medication: discontinuation of NSAID, ACE inhibitors, aminoglycosides or other nephrotoxic drugs.
• Low potassium, low-protein but high-caloric diet.
• Fluid balance depending on body temperature, body weight and urine production

Urinary Drainage:

Insert a bladder catheter to measure diuresis or also therapeutically for postrenal AKI. For patients with hydronephrosis without urinary retention, depending on the laboratory result (potassium, urea, acidosis), an elective or urgent upper urinary tract drainage with DJ ureteral splints or percutaneous nephrostomy is indicated.

Treatment of Hyperkalemia

Hyperkalemia can be treated with administrating intravenous glucose/insulin (500 ml glucose 5% with 10 IU of insulin i.v.) or potassium binders p.o. In acidosis, sodium bicarbonate i.v. should be considered; this also improves hyperkalemia. Hyperkalemia refractory to treatment is an indication of dialysis.

Diuretics

Diuretics are often used as a therapeutic trial (e.g., furosemide up to 40 mg/h or mannitol). In controlled studies, diuretics did not reduce the mortality rate or the need for dialysis. Diuretics are a treatment option in case of volume overload, if the medication leads to an increase in diuresis.

Dialysis

Indications for dialysis are hyperkalemia >6.5 mmol/l, severe metabolic acidosis, pulmonary edema, urea >200 mg/dl, and symptoms of uremia (e.g., pericarditis or neurological symptoms).

Hemodialysis or hemofiltration:

Hemodialysis or hemofiltration is the method of choice for treating acute renal failure in adults.

Peritoneal dialysis:

Peritoneal dialysis requires the implantation of a peritoneal catheter and is indicated for treating renal failure in infants and young children.

Prognosis of Acute Renal Failure

See also section epidemiology for prognosis. Renal function is recovering in the surviving patients within 2–3 months. 20–60% of patients in need of dialysis will become independent of kidney replacement procedures again. However, 8–21% of these patients will again need dialysis within 2–3 years.

References

Klahr und Miller 1998 KLAHR, S. ; MILLER, S. B.: Acute oliguria.
In: N Engl J Med
338 (1998), Nr. 10, S. 671–5

Lameire u.a. 2005 LAMEIRE, N. ; VAN BIESEN, W. ; VANHOLDER, R.: Acute renal failure.
In: Lancet
365 (2005), Nr. 9457, S. 417–30

Schrier und Wang 2004 SCHRIER, R. W. ; WANG, W.: Acute renal failure and sepsis.
In: N Engl J Med
351 (2004), Nr. 2, S. 159–69

Thadhani u.a. 1996 THADHANI, R. ; PASCUAL, M. ; BONVENTRE, J. V.: Acute renal failure.
In: N Engl J Med
334 (1996), Nr. 22, S. 1448–60

  Deutsche Version: Therapie der akuten Niereninsuffizienz