Dr. med. Dirk Manski

 You are here: Urology Textbook > Kidneys > Renal insufficiency > Acute renal injury

Acute Kidney Injury – Acute Renal Failure (1/2)

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

Definition of Acute Kidney Injury

Acute kidney injury (AKI) is an abrupt (within 48 hours) worsening in kidney function with an increase in serum creatinine. Acute kidney injury is classified according to table AKIN classifikation of acute kidney injury.

Definitions of Urine Output

The urine output alone is not a good parameter to predict renal function, as acute renal failure may be present with polyuria, oliguria or anuria.

Classification of acute kidney injury after criteria of AKIN (Acute Kidney Injury Network).
(*) Classification after exclusion of an obstruction of the urinary tract and after sufficient hydration. The rise of creatinine is calculated from known or suspected baseline values.
AKIN serume creatinine urine output (*)
1 1,5–1,9fold rise of creatinine or rise ≥0,3 mg/dl <0,5 ml per kg body weight per hour lasting 6–12 h
2 2–2,9fold rise of creatinine <0,5 ml per kg body weight per hour lasting over 12 h
3 >3fold rise of creatinine or
serum creatinine >4 mg/dl with a rise more than 0,5 mg/dl or
necessity of dialysis
<0.3 ml per kg body weight per hour lasting more than 24 h or anuria more than 12h

Epidemiology of Acute Kidney Injury

Community acquired AKI:

Incidence 2 per 1000 per year in Europe.

Hospital acquired AKI:

10–20% of hospital patients suffer from acute kidney failure and up to 35–60% of patients admitted on intensive care units. On ICU, mortality increases to 60% when dialysis becomes necessary (Alscher et al, 2019).

Etiology of Acute Kidney Injury

Prerenal AKI

Worsening of kidney function due to poor kidney conditions (55% of all AKI). The most common reason is decreased renal blood flow, by definition there is no kidney disease or urinary drainage disorder.

Intravascular volume depletion:

Trauma, burns, bleeding, allergic shock, sepsis, pancreatitis, dehydration.

Decreased cardiac output:

Acute heart diseases such as myocardial ischemia or other heart diseases (cardiorenal syndrome), pulmonary embolism or decreased cardiac output due to mechanical ventilation.

Decreased renal blood flow:

Medication with ACE inhibitors or NSAID, anesthesia, hepatorenal syndrome, hyperviscosity syndrome in multiple myeloma or polycythemia.

Renal Kidney Failure

The failure of renal function is due to renal diseases (45% of all AKI).

Renal vessel diseases:

Microvascular diseases:

Tubulointerstitial diseases:

Acute tubular necrosis:

Ischemia or toxic substances cause tubular epithelial damage, worsening of kidney function is exacerbated by necrotic cells that clog the tubules. Kidney function may recover after the cells have been repaired.

In the case of toxic substances, tubular necrosis is caused either by ischemia (e.g. vasoconstriction by contrast medium) or direct cell damage (e.g. cisplatin). Further toxic substances are aminoglycosides, antibiotics, antifungals, chemotherapeutics, chemicals (heavy metals, solvents, insecticides), drugs (heroin, amphetamines) or D-penicillamine. Endogenous causes are free hemoglobin (hemolysis) or myoglobin (rhabdomyolysis).

Postrenal Kidney Failure

Postrenal kidney failure is the worsening of kidney function due to insufficient urine drainage (5% of all AKI).

Pathophysiology of Acute Kidney Injury

Excess of Extracellular Fluid Volume

Acute kidney injury causes a reduced salt and water excretion. This leads to weight gain, dyspnea and pulmonary edema.


Potassium increases 0.5 mmol/l/day during anuria. Additional cell disintegration (tumor lysis, hemolysis, rhabdomyolysis) leads to particularly serious hyperkalaemia.

Metabolic Acidosis

Diminished excretion of protons leads to metabolic acidosis. Acidosis can be aggravated by corresponding underlying diseases: diabetic ketoacidosis, lactic acidosis, liver diseases and tissue ischemia.

Hyperphosphatemia and Hypocalcemia

Hyperphosphatemia and hypocalcemia develops due to secondary hyperparathyroidism.


Acute kidney injury leads to a decreased renal erythropoietin secretion, hemodilution and decreased survival of erythrocytes. The risk of bleeding is increased due to dysfunction of thrombocytes.

Signs and Symptoms of Acute Kidney Injury

Uremia resulting from acute renal failure causes non-specific complaints. The underlying disease for the acute kidney injury is crucial for most of the symptoms.

Symptoms of Prerenal Kidney Failure

Symptoms of Renal Kidney Failure

Usually, a risk situation for renal ischemia or toxic renal damage is observable.

Symptoms of Postrenal Kidney Failure

Flank pain, abdominal pain or neurological symptoms are suspicious for a postrenal kidney failure.

Symptoms due to Complications of Acute Kidney Injury

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.
In: Lancet
365 (2005), Nr. 9457, S. 417–30

Mehta, R. L.; Kellum, J. A.; Shah, S. V.; Molitoris, B. A.; Ronco, C.; Warnock, D. G.; Levin, A. & AKIN
Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury.
Crit Care, 2007, 11, R31.

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: Akute Niereninsuffizienz