Brief overview
- Symptoms: Decreased urine output, easy fatigability, impaired concentration, nausea, water retention, shortness of breath, cardiac arrhythmias, dizziness, unconsciousness.
- Course and Prognosis: With timely treatment, the kidney may recover completely during the recovery phase; however, the disease is sometimes fatal.
- Causes: Decreased renal blood flow (e.g., due to large fluid losses), renal damage due to other kidney diseases, medications, or bacterial and viral infections, obstructed urinary flow (e.g., due to kidney stones)
- Diagnosis: Blood and urine tests, imaging procedures, especially ultrasound examination
- Treatment: Depending on the cause, for example, removal of kidney stones, administration of antibiotics for infections, discontinuation of certain medications, fluid intake and dialysis if required
- Prevention: People with impaired kidney function in particular should only use over-the-counter medications after consulting their doctor.
What is acute renal failure?
In acute kidney failure (acute renal insufficiency or kidney weakness), kidney function deteriorates drastically within a short time: the volume of fluid that the kidneys normally filter per unit of time drops rapidly.
Acute kidney failure causes substances to accumulate in the blood that are actually excreted in the urine. These so-called urinary substances include urea and creatinine. If they accumulate in the body, this leads to gradual urine poisoning. Physicians refer to this as uremia.
In most cases of acute kidney failure, the function of other organs is also impaired. Acute renal failure is therefore a potentially life-threatening condition and always an emergency.
Acute renal failure is particularly common in people receiving intensive care in hospital: Up to 39 percent of all intensive care patients are affected. In principle, acute kidney failure – unlike chronic kidney failure – is reversible. This means that the kidney may recover from an almost complete acute loss of function. However, this is not the case for all sufferers.
What are the symptoms of acute kidney failure?
You can read about the symptoms of acute renal failure in the article Renal failure symptoms.
Acute kidney failure: What are the stages?
In most cases, acute kidney failure progresses through four stages or phases:
- Damage phase (initial phase): It lasts a few hours to days, and there are no symptoms yet.
- Oligo or anuric phase: In this stage, urine output decreases significantly until little (oligouria) or virtually no urine (anuria) leaves the body. This phase generally lasts for ten days.
- Diuretic or polyuric phase: as the kidneys recover, they produce more and more urine (up to five liters or more per day). This phase lasts about three weeks, the main danger being the high losses of water and the electrolytes it contains, sodium and potassium.
- Recovery phase: in this last stage, which lasts up to two years, the kidney cells more or less regain their functional capacity.
The prognosis for acute kidney failure varies accordingly. It depends above all on the severity of the underlying disease. If acute kidney failure is treated in time and the patient is not severely weakened by other pre-existing conditions, kidney function may recover under certain circumstances, sometimes even completely.
However, about ten percent of those affected remain permanently dependent on dialysis. In addition, the risk of cardiovascular disease is increased after acute renal failure.
On the other hand, the prognosis is worse, especially in intensive care patients, and the mortality associated with acute kidney failure is relatively high at up to 60 percent.
Causes and risk factors
Depending on the cause, doctors divide acute kidney failure into the following forms:
Prerenal kidney failure
Prerenal kidney failure (about 60 percent of cases) is due to reduced blood flow to the kidneys. The most common cause is blood and fluid loss due to major surgery, accidents or burns. Changes in renal blood flow caused by certain medications (X-ray contrast media, ACE inhibitors or antibiotics) also sometimes cause prerenal renal failure.
Renal kidney failure
Renal acute kidney failure (about 35 percent of all cases) results from direct damage to kidney tissue, usually due to inadequate oxygen supply. Such damage occurs, for example, as a result of inflammation, such as non-bacterial kidney inflammation (glomerulonephritis), vascular inflammation (vasculitis) or blood clots (thromboembolism).
Kidney infections with bacteria (renal pelvic inflammation) or viruses (interstitial nephritis), as well as toxic substances and drugs (for example, certain antibiotics), also damage the kidneys in some cases and trigger acute kidney failure.
Postrenal renal failure
The cause of postrenal kidney failure (about five percent of all cases) is an obstruction of the urine outflow. For example, kidney stones, tumors, congenital malformations and prostate enlargement interfere with urine outflow and thus promote acute kidney failure.
Examinations and diagnosis
To diagnose acute renal failure and determine the possible cause, the physician takes the patient’s medical history and performs various examinations:
Blood test
In addition, there are changes in blood salts, especially an increase in potassium levels. The blood count and other blood values (such as liver values, C-reactive protein and others) also provide important indications of acute kidney failure in some cases.
Urinalysis
Very important for the diagnosis of “acute kidney failure” is the detection of protein in the urine, which is normally not or hardly found there. In addition, the physician determines, among other things, the glomerular filtration rate (GFR), the amount of urine, the specific gravity and the salt content of the urine.
Ultrasound examination
An ultrasound examination (sonography) of the kidneys and urinary tract is routine when examining an individual with suspected acute renal failure. If postrenal renal failure is present, the causative urinary outflow obstruction (such as that caused by a kidney stone) can be identified on ultrasound. In addition, in acute renal failure, the kidneys are usually enlarged.
In some cases, further tests are necessary to determine the cause of acute kidney failure, such as an X-ray of the kidney or the removal of a tissue sample (kidney biopsy).
The AKIN criteria: When is acute kidney failure present?
- Creatinine increases by 0.3 milligrams per deciliter in acute renal failure.
- The percent creatinine increase is 1.5 times the baseline value.
- Or urine output decreases to less than 0.5 milliliters per kilogram of body weight per hour for more than six hours.
Treatment
Doctors treat acute kidney failure in a variety of ways – depending on severity, causes or underlying disease. For example, if kidney stones are responsible for acute kidney failure by obstructing the flow of urine, it is necessary to remove them. Bacterial inflammations can be treated with antibiotics and harmful drugs can be reduced in dosage. Sometimes it is even necessary to discontinue them altogether.
Doctors compensate for severe blood and fluid losses (for example, due to accidents) with the help of infusions. The administration of fluids in the form of infusions is also important during the period when the kidneys are recovering from the insufficiency.
If acute kidney failure has (almost) completely paralyzed urine production, doctors also administer diuretics. If these measures do not improve kidney function, the blood is artificially cleansed (dialysis) until the kidneys are again able to take over the blood cleansing and excretory function on their own.
Nutrition in acute renal failure
You can read about how nutrition can support the treatment of acute kidney failure in the article Nutrition in renal failure.
Prevention
Acute kidney failure cannot be prevented in principle. However, during and after major surgery, doctors closely monitor blood volume, blood pressure and fluid balance to reduce the risk of acute renal failure.
Many drugs promote kidney damage and thus trigger acute kidney failure in some cases. These include over-the-counter preparations such as certain painkillers (for example, paracetamol, ibuprofen, diclofenac). It is therefore advisable to discuss any use of medication with your doctor. This is especially true for people with existing kidney disease and impaired kidney function – they are particularly susceptible to acute kidney failure.
