Acute renal failure (ARF)

What is it?

Acute Renal Failure is characterised by a rapid deterioration of renal function and its clinical picture varies greatly depending on its cause and severity. The risk of developing acute renal failure is particularly high in elderly patients, as they have reduced renal function, largely dominated by the simultaneous use of several medications, and have concomitant predisposing diseases. In hospitalised patients, the incidence of acute renal failure is steadily increasing: most cases have toxic causes, mainly iatrogenic, as well as a high incidence in patients undergoing surgery. Acute renal failure can be classified as follows: 1) prerenal: the kidney is the victim of a general haemodynamic alteration (50-80% of cases of AKI), resulting from a reduction in circulating volume, with consequent reduced renal perfusion as in the case of dehydration, heart failure, sepsis, etc. 2) Renal: primary damage to the renal parenchyma: the causes are numerous and can vary according to the age of the patient. In hospitalised patients the main cause of AKI is acute tubular necrosis, while in children it is acute glomerulonephritis and uremic-haemolytic syndrome. 3) Post-renal: his form is more common in elderly men and is due to obstruction of the urinary tract, which involves gradual distension of the ureter and renal pelvis and reduces glomerular filtration pressure.

Which are the symptoms?

Acute renal failure can be a clinical emergency as it can be accompanied by pulmonary oedema or peripheral oedema due to overload with extracellular fluid volume, and electrolyte disturbances such as hyperkalemia, changes in blood sodium levels and acid-base status due to loss of renal regulatory function.

·         edema

·         pulmonary oedema

·         changes in blood tests

How is it diagnosed?

For diagnostic purposes, it is important to identify concomitant chronic diseases, recent infections, taking any nephrotoxic drugs (paying special attention to over-the-counter medications such as NSAIDs, herbal preparations), exposure to toxic substances in the workplace, etc. These can all be risk factors for the development of parenchymal acute renal failure. The diagnosis is made on the basis of signs of reduced renal function, which can be assessed by an increase in blood creatinine and nitrogen levels compared to baseline values. In addition, there may be changes in plasma electrolyte concentrations (sodium, potassium and bicarbonate). Another important clinical criterion is a decrease in diuresis, which must be less than 0.5 ml/kg/h for 6-12 hours to be diagnostically significant. Anuria (diuresis less than 100 ml in 24 hours) suggests complete obstruction of the urinary tract, but can also complicate severe forms of renal or pre-renal AKI. Urinalysis is of fundamental importance in the diagnosis of AKI, facilitating the differential diagnosis between functional and organic forms: turbid urine or pyuria may indicate pyelonephritis. With regard to instrumental diagnosis, urinary ultrasound is an indispensable examination in the primary approach for patients with acute renal failure.

Suggested exams

How is it treated?

Patients who are exposed to risk factors for AKI should take preventive measures: essentially, they should avoid exposure to potentially nephrotoxic agents or the use of potentially nephrotoxic drugs. Treatment aims to address the underlying cause of renal failure, so adequate renal perfusion should be restored to ensure maintenance of diuresis and good renal function.

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