Acute Renal Failure

Renal insufficiency is the term that applies to the kidneys which cannot perform their duties properly.

Renal failure can be acute or chronic. The first occurs when the loss of kidney function is permanent and often progressive; the second is a process that occurs suddenly and usually lasts less than three months, and there may be complete or incomplete recovery of renal function.

An acute renal failure may turn into chronic if the injury is severe and there is no complete recovery. Similarly, a person with chronic low but stable renal function may suffer some aggression in their kidneys, sharpening their renal and leading to a sharp drop in its function.

Before speaking of acute renal failure itself, learn some explanations.


Renal function

Both kidneys filter on average 180 liters of blood per day, about 120 ml per minute. This value is called whitening kidney (renal clearance) or glomerular filtration rate (glomerulus is the basic unit of the kidney, as the neuron is for brain).

Function of kidney
Normal renal function is one that lies between 70 and 140 ml / min blood filtrate per day. This value varies with age, size and sex. When the clearance is less than 70ml/min there is renal failure and when it is higher than 140 ml / min it is called hyperfiltration, which is also a sign of renal disease (very common in diabetics).

As we age, our kidneys also decrease their ability to function. Seniors have up to 30% smaller kidneys than when they are young. Therefore, it is not surprising that older people may have rates up to 60 ml / min without necessarily having any kidney disease. Kidneys are "healthy", but old and less resistant to damage.

For practical purposes, consider chronic renal failure when the glomerular filtration rate remains below 60 ml / min over 3 months and renal abruptly decreases for at least 25% in renal function regardless of the previous value. As the kidneys filter on average somewhere around 100 ml / min of blood, often physicians use the value in percentage to facilitate understanding. Thus, a filtration rate of 50 ml / min can be considered as running kidneys 50%.

When we speak of renal function we always mean both kidneys. If the doctor tells you that your kidney function is 40% or 40 ml / min, this means the total function of the two kidneys together.

There is no way to measure renal filtration directly, so laboratory tests are used. One is the 24-hour urine, where all urine excreted during a day is collected in one or more cylinders. This urine is then sent to a laboratory which can evaluate the rate of renal filtration. This exam is very annoying to do, besides being very common patient it is possible to make a mistake during the collection day. So nowadays the function of the kidneys is preferred to be evaluated through the measurement of creatinine in the blood.

With the values of creatinine in the blood renal function can be estimated by mathematical calculations. Normally laboratories already automatically do this calculation and the result comes in the name of creatinine clearance. Creatinine clearance equals glomerular filtration rate.

Well, the explanations are over so let's get to it.

What is ARF?

Acute renal failure occurs when there is some kidney injury with rapid decline in kidney function. This is reflected by a rapid rise in blood creatinine value. As mentioned above, it can occur in people with normal kidneys as in chronic renal failure.

In more severe cases patients can develop the disease requiring hemodialysis in just 24 to 48 hours.

Usually hemodialysis is indicated when renal function falls below 20 ml / min or when there is no clear signs of kidney function such as blood severe acidosis, excess blood potassium, neurological by renal failure, or when the patient urine is under 100 ml per 24 hours.


The main causes of acute renal failure are:
Acute renal failure causes
Acute renal failure causes
  • Circulatory shock
  • Sepsis
  • Dehydration
  • Burns extended
  • Excess diuretics
  • Rhabdomyolysis (muscle injury with extensive in case of polytrauma)
  • Renal obstruction by an enlarged prostate
  • Severe heart failure
  • Acute glomerulonephritis

Several drugs are toxic to the kidneys and can lead to acute renal failure:
  • Anti-inflammatory drugs
  • Antibiotics, particularly the family of aminoglycosides (e.g. gentamicin and amikacin)
  • Some chemotherapeutic
  • Iodine based contrast to radiological
  • Lithium
  • Acyclovir
  • Heroin
  • Pesticides
  • Carambola
  • Chinese herbs

Some causes of acute renal failure are preventable, especially in people with already impaired renal function or elderly. A good example is not abusing anti-inflammatory and preventing radiological contrasts with the intravenous iodine based in this group of patients.

Not everyone who develops acute renal failure needs dialysis. The younger and healthier the patient is, the more likely their kidneys withstand severe injuries. Similarly, not all kidney injury is severe enough to cause a major loss of kidney function.

Imagine a person with a filtration rate of 120 ml / min which undergoes severe intoxication by any nephrotoxic substance (toxic to the kidneys), losing 60 ml / min of their renal function. It will still be a filtration with approximately 60 ml / min which is enough to keep the patient out of hemodialysis. Have the same situation in an elderly patient or someone with already known renal disease and a prior filtration rate between 40 and 60 ml / min will surely end in hemodialysis.

Recovery of renal function

Recovery from acute renal failure depends on several factors, including age, association with other diseases and renal function before the injury. Some function recovers completely, with other function to be permanently below 60 ml / min, and there are those that won't recover, staying dependent on dialysis for life.

Kidney failure is a common complication of severe patients, especially those admitted to ICU, and is one of the main factors that increases the mortality rate in this group.

Any person showing some aggression may develop kidney with acute renal failure, but it is more common and more severe when it occurs in patients with renal disease.

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