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Acute Kidney Injury – Acute Renal Failure (2/2)
- Acute kidney injury – acute renal failure (1/2): causes, pathophysiology and symptoms
- Acute kidney injury – acute renal failure (2/2): 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
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 sediment and urine culture, 24-hour urine collection with measurement of creatinine, electrolytes, protein excretion, osmolality, pH.
Differential Diagnosis of Urine Sediment in AKI:
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, uric acid crystals may be seen in tumor lysis syndrome.
to identify bacteriuria.
24 h urine:
In a collection of 24 h urine the following parameters are measured: creatinine, electrolytes, protein, osmolality and pH.
Sodium excretion in the urine can distinguish between prerenal or renal causes of acute kidney injury. In case of tubular dysfunction, the sodium is not reabsorbed and high urinary sodium concentrations result. A urinary sodium concentration of less than 10 mmol/l is typical for a prerenal kidney failure.
The fractional sodium excretion (FeNa) calculates the sodium excretion in relation to the creatinine excretion, see formula FeNa. The concentrations of sodium in the urine and plasma (UNa and PNa) and the concentrations of creatinine in urine and plasma (UKrea and PKrea) are needed. A FeNa less than 1 suggests a renal kidney failure and a FeNa of more than 1 a prerenal kidney failure:
|Calculation of FeNa|
- complete blood count
- blood gas analysis
- creatinine, uric acid, urea
- LDH, CK, lipase, liver enzymes
- protein electrophoresis, albumin
- clotting tests
Ultrasound imaging determines kidney size, renal blood flow and RI. Important is the exclusion of an obstructive uropathy and urinary retention. Further abdominal ultrasound of the other organs is necessary to detect underlying diseases (e.g. liver diseases, ileus or ascites).
Abdominal CT without contrast agents can be done to rule out a postrenal kidney failure, if renal ultrasound imaging is equivocal.
Renal biopsy is indicated in acute renal failure with a nephritic urine sediment: (micro)hematuria, dysmorphic red blood cells, urinary casts with red blood cells and proteinuria.
Treatment of Acute Renal Failure
- 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
Insertion of a bladder catheter to control the excretion 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 urinary diversion with DJ ureteral splints or percutaneous nephrostomy is indicated. This also applies to persistent hydronephrosis and AKI after treatment of urinary retention.
Treatment of Hyperkalemia
Hyperkalemia can be treated with the administration of glucose/insulin (500 ml glucose 5% with 10 IU of insulin i.v.) or potassium binders p.o. In acidosis, the administration of sodium bicarbonate should be considered, this also improves the hyperkalemia. A progressive hyperkalemia is an indication for dialysis.
Diuretics are often used as a therapeutic trial (e.g. furosemide up to 40 mg/h or mannitol). In controlled studies, the mortality rate or the need for dialysis was not reduced with the use of diuretics. Encouraging results are reported for the use of atrial natriuretic factor (ANF).
Indications for dialysis are: hyperkalemia >6.5 mmol/l, severe metabolic acidosis, pulmonary edema, urea >200 mg/dl, symptoms of uremia (e.g. pericarditis or neurological symptoms).
Hemodialysis or hemofiltration:
Hemodialysis or hemofiltration is the method of choice for the treatment of acute renal failure in adults. Please see section dialysis.
Peritoneal dialysis requires the implantation of a peritoneal catheter and is indicated for the treatment of 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 month. 20–60% of patients in need of dialysis will become independent of kidney replacement procedures. However, 8–21% of these patients will again need dialysis within 2–3 years.
|ARF Causes||Index||kidney diseases|
Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
- 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.
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