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Acute renal failure (ARF), also known as acute kidney failure or acute kidney injury, is a rapid loss of renal function due to damage to the kidneys, resulting in retention of nitrogenous (urea and creatinine) and non-nitrogenous waste products that are normally excreted by the kidney. Depending on the severity and duration of the renal dysfunction, this accumulation is accompanied by metabolic disturbances, such as metabolic acidosis (acidification of the blood) and hyperkalaemia (elevated potassium levels), changes in body fluid balance, and effects on many other organ systems. It can be characterised by oliguria or anuria (decrease or cessation of urine production), although nonoliguric ARF may occur. It is a serious disease and treated as a medical emergency.
Acute renal failure is usually categorised (as in the flowchart below) according to pre-renal, renal and post-renal causes.
In general, renal failure is diagnosed when either creatinine or blood urea nitrogen tests are markedly elevated in an ill patient, especially when oliguria is present. Previous measurements of renal function may offer comparison, which is especially important if a patient is known to have chronic renal failure as well. If the cause is not apparent, a large amount of blood tests and examination of a urine specimen is typically performed to elucidate the cause of acute renal failure, medical ultrasonography of the renal tract is essential to rule out obstruction of the urinary tract.
Consensus criteria (RIFLE)[1][2] for the diagnosis of ARF are:
Kidney biopsy may be performed in the setting of acute renal failure, to provide a definitive diagnosis and sometimes an idea of the prognosis, unless the cause is clear and appropriate screening investigations are reassuringly negative.
Acute renal failure may be reversible if treated promptly and appropriately. Resuscitation to normotension and a normal cardiac output is key. The main interventions are monitoring fluid intake and output as closely as possible; insertion of a urinary catheter is useful for monitoring urine output as well as relieving possible bladder outlet obstruction, such as with an enlarged prostate. In the absence of fluid overload, administering intravenous fluids is typically the first step to improve renal function. Fluid administration may be monitored with the use of a central venous catheter to avoid over- or under-replacement of fluid. If the cause is obstruction of the urinary tract, relief of the obstruction (with a nephrostomy or urinary catheter) may be necessary. Metabolic acidosis and hyperkalemia, the two most serious biochemical manifestations of acute renal failure, may require medical treatment with sodium bicarbonate administration and antihyperkalemic measures, unless dialysis is required.
Should hypotension prove a persistent problem in the fluid replete patient, inotropes such as norepinephrine and/or dobutamine may be given to improve cardiac output and hence renal perfusion. While a useful pressor, there is no evidence to suggest that dopamine is of any specific benefit,[3] and at least a suggestion of possible harm. A Swan-Ganz catheter may be used, to measure pulmonary artery occlusion pressure to provide a guide to left atrial pressure (and thus left heart function) as a target for inotropic support.
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