Acute renal failure (Acute renal insufficiency)

The kidneys are probably one of the organs we think about the least. We consume all kinds of food and toxins, and do not think at all that our kidneys have to excrete a large part of the potentially harmful substances again. In addition, the kidneys regulate the water and electrolyte balance and keep blood pressure stable.

Only in the case of acute kidney failure or chronic renal insufficiency does one realize how important these small organs are. In acute renal failure, the kidneys fail completely within a few hours or days. The good news is that this can usually be treated so well that the kidney functions properly again afterwards.

The causes of acute renal failure can in principle be divided into three groups. These include the prerenal causes, which exist outside the kidney and affect its circulation, the renal causes, which are directly due to diseases of the kidney, and the postrenal causes, which are due to disturbances in the outflow system from the kidney.

Prerenal causes

If the kidney does not have a good blood supply, it naturally cannot function. For example, high fluid loss due to bleeding, vomiting, diarrhea, or extensive burns can lead to poor renal blood flow and thus acute kidney failure.

However, low blood pressure, blockage of renal vessels, or certain medications that affect wall tension in the renal vessels can also cause acute renal failure.

Renal causes

The main cause is inflammation of the kidney, which reduces the organ's ability to function. But also drugs or toxins can destroy the kidney, especially if they are taken in too large quantities.

In children, acute renal failure is usually caused by Gasser's syndrome (haemolytic uraemic syndrome). In this case, after an infection, small blood clots are formed which then block the kidney vessels and thus impair their function.

Postrenal causes

In the area of the urinary tract, stones, tumours or enlargement of the prostate play a major role. All these causes constrict the ureter, causing urine to back up into the kidney.

In acute renal failure, the symptoms depend very much on the triggering cause. However, with suitable test procedures, certain parameters can still be collected that indicate renal failure.

Symptoms of the early phase

In the so-called early phase, the main symptoms are a reduction in urine output or a lack of urine output. Since no healthy person keeps a log of their own toilet use, this remains undetected for a long time.

More obvious here can be the typical signs of overhydration. These include, for example, water retention in the arms and legs, in the lungs or in the brain. In many cases, these are very easy to diagnose.

During this phase, the so-called uremic symptoms of chronic renal insufficiency are also developed to a greater or lesser extent.

Overview of the uremic symptoms

• General: weakness, water retention, urine odour
• Cardiovascular system: high blood pressure, cardiac arrhythmia
• Lungs: water retention, pneumonia, pleurisy
• Blood: anaemia, coagulation disorder
• Bones: Bone pain, tendency to fracture
• Digestive tract: gastroenteritis
• Brain: lack of concentration, impaired consciousness, pain
• Hormonal system: impotence disorder, cycle disorder, loss of libido

Symptoms in the late phase

In the late phase, the complete failure of the filtering function of the kidney sometimes leads to excessive urination. Instead of the filtered fluid being returned to the body, the kidney simply excretes it all. This of course leads within a very short time to considerable disturbances in the water and electrolyte balance, which can also be fatal.

To diagnose acute renal failure, the underlying disease must be correctly diagnosed first and foremost. The fact that damage to the kidney has actually occurred is usually only found out if an explicit search is made for it.

Accurate balancing of input and output

If there is a possible kidney damage, the fluid intake, as well as the fluid loss and the body weight must be written down and checked in detail. This is the most effective way to determine if the kidneys are still functioning.

Blood tests provide further clues

Further clues can be obtained from blood tests, in which mainly urea and electrolytes are measured. If there is a disorder of the kidneys, there will be correspondingly increased or decreased values.

Examination of the urine

Obviously, the product of the kidneys, the urine, must also be examined. Here, for example, attention is paid to whether cells that should not normally be there can be found. These include, for example, certain proteins or white blood cells or the blood pigment.

In addition, the extent to which the urine could be concentrated or not is also measured. Highly diluted urine is just as indicative of kidney damage as urine that is too concentrated.

Further examinations

The kidney can also be examined directly. For example, an ultrasound can be used to determine whether the kidneys are the right size and consistency. A so-called colour Doppler can also check whether the kidney is well supplied with blood.

An X-ray of the chest can determine whether there is already water retention in the lungs.

If the other examinations do not give a clear indication of how the kidneys are doing, a kidney biopsy must be taken. A small piece of the kidney is removed via a needle and examined in a laboratory.

In the treatment of acute renal failure, the focus is on treating the disease that caused the condition. In addition, all substances that damage the kidneys should be discontinued immediately. This is because even the smallest amounts of renal toxins are unacceptable in cases of pre-existing kidney damage.

Monitoring of body functions

In addition to combating the underlying disease, it is above all the bodily functions that must be constantly monitored. This includes not only close monitoring of the amounts of fluids taken in and given out, but also daily urine and blood tests.

These then also provide precise information about the electrolyte situation, which must be corrected immediately if necessary. To regulate the water balance, so-called diuretics can also be given, which have a dehydrating effect.

Dose adjustment of all medications

Many medications are excreted through the kidneys. If the kidney is no longer functioning or is only doing its job to a limited extent, then the dose of the medication given must of course also be reduced. Otherwise, the level of active substances in the blood would be too high and the kidney would be unnecessarily burdened.

Dialysis therapy

This is often used at a very early stage in acute renal insufficiency because it is usually only required temporarily. The function of the kidney is taken over by a machine that washes the blood, so to speak. Harmful substances are filtered out, thus optimising the fluid and electrolyte balance.

If the kidney failure occurs in the context of a so-called multi-organ failure, then the prognosis is very poor. Because if the kidneys then also fail, this is a clear sign that the organism can no longer hold out for much longer. In this case, the mortality rate is about 50%.

However, if the underlying disease that led to the kidney problems can be adequately treated and cured, then the chances are good that the kidneys will regain their normal functionality. For this to happen, of course, they must be adequately spared and relieved to support their recovery.