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

Medical History

Main goal is the differentiation between acute exacerbation of chronic renal failure or acute kidney injury without preexisting renal disease: shock? Lack of volume? Toxins? Drugs? Symptoms of systemic diseases? Known renal diseases?

Urine

Urine sediment:

An inconspicuous urine sediment indicates a prerenal, postrenal vascular kidney failure. Urinary casts with granulocytes are typical for tubular necrosis and with erythrocytes are typical for glomerulonephritis. Leukocyturia indicates interstitial nephritis or pyelonephritis. Uric acid crystals may be seen in tumor lysis syndrome.

Urine culture:

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 (U_Na and P_Na) and the concentrations of creatinine in urine and plasma (U_Krea and P_Krea) are needed. A FeNa less than 1 suggests a renal kidney failure and a FeNa of more than 1 a prerenal kidney failure:

$formula to calculate the fractional sodium excretion of acute renal failure$

Calculation of FeNa

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. 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

Abdominal CT without contrast agents can be done to rule out a postrenal kidney failure, if renal ultrasound imaging is equivocal.

Renal Biopsy

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

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

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

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. Partial encouraging results are reported for the use of atrial natriuretic factor (ANF).

Dialysis

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:

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

The mortality rate of acute renal failure is 50%. The high mortality rate, however, is due to the underlying diseases like sepsis, trauma and shock.

Renal function is recovering in the surviving patients within 2–3 weeks. In 50%, permanent kidney damage will remain. The risk of chronic dialysis depends on the underlying disease and is about 5%. Another 5% will have a progressive chronic renal failure with later end-stage renal disease.

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

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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

Last update

Dr. med. Dirk Manski
man...@urologielehrbuch.de