Acute Kidney Failure - Specialists and Information

The kidneys are among the smallest organs in the body. At the same time, however, they are the organs with the highest blood flow, both at rest and during physical exertion. The kidneys perform a wide variety of functions in the human body (Figure 1). Doctors and patients often underestimate the importance of the kidneys.

Figure 1: Functions of the kidneys in the human body

Acute kidney failure can occur in individuals with perfectly healthy kidneys (acute) or in those with a known kidney disease (acute-on-chronic).

In contrast to chronic kidney failure, acute kidney failure is characterized by a sudden loss of kidney function. In most cases, the decline in kidney function occurs within a few days.

The incidence of acute kidney failure has been rising for the past 7 years.

This applies to both hospital-acquired cases (by far the largest group) and community-acquired cases. Acute and chronic kidney failure are among the most common causes of long-term dialysis in the United States.

The causes are varied. The following classification has proven useful:

• prerenal acute kidney failure
• renal acute kidney failure
• and postrenal acute kidney failure

Any severe organ disease or circulatory disorder affecting the kidneys can lead to kidney failure. The most common causes are blood loss, dehydration, and shock. Severe heart or liver disease can also lead to kidney failure.

Another common cause of acute kidney failure is prior contrast-enhanced imaging. The number of unreported cases of renal insufficiency following cardiac catheterization is high. However, since the rise in creatinine levels does not occur until 24 to 48 hours after contrast agent administration, patients have already been discharged from the hospital by that time.

Approximately 1 percent of patients who previously had healthy kidneys require dialysis following a cardiac catheterization. Kidney failure increases the in-hospital mortality rate among heart patients from 1 percent to 36 percent. Between 13 and 50 percent of patients who require dialysis after contrast agent administration remain on permanent dialysis.

In addition to pain medications, blood pressure medications, and diuretics, the following conditions can cause renal insufficiency:

• Renal embolisms
• Cholesterol embolisms
• Plasmacytoma
• Muscle breakdown
• Obstruction of the urinary tract (ureter, bladder, urethra)

Acute kidney failure initially presents without symptoms, so doctors and patients often do not notice it. Urine output is often preserved.

Only when the kidneys have lost 90 percent of their function does reduced urine output occur. In addition, high blood pressure, fluid retention, and shortness of breath develop.

Renal failure, which used to be fatal in all cases, now presents with nonspecific symptoms such as:

• Decreased energy levels
• Loss of appetite
• Nausea and vomiting
• Sensory disturbances
• Heart rhythm disturbances
• Confusion
• Cramps

In the early stages, a doctor can only detect acute kidney failure by measuring kidney function. To do this, the doctor measures serum creatinine in the blood and then converts it to an estimate of kidney function (glomerular filtration rate, GFR) (Figure 2).

This conversion is necessary because serum creatinine levels depend on gender, age, muscle mass, dietary intake, and fluid intake.

However, it does not reflect the current state of kidney function if creatinine has not had enough time to accumulate in the body. Serum creatinine is then low, even though kidney function is already significantly reduced.

Even during dialysis, kidney function can no longer be measured by serum creatinine, since dialysis removes creatinine.

Figure 2: Kidney function is most commonly assessed using serum creatinine levels. There is a quadratic relationship between creatinine and kidney function. Therefore, even small increases in serum creatinine (e.g., 0.3 mg/dl) can contribute to a significant loss of kidney function (e.g., 50%).

There are different stages of acute kidney failure (Figure 3).

Figure 3: Classification of the stages of acute kidney injury.

To make a diagnosis, doctors perform a blood test, a urinalysis, and an ultrasound examination of the kidneys. The ultrasound rules out chronic or postrenal kidney failure.

In rare cases, a duplex ultrasound of the kidneys can confirm a circulatory disorder. Computed tomography (CT) enables the diagnosis of a renal artery embolism.

If the cause of acute kidney failure cannot be determined using these methods, a kidney biopsy must be performed. Ideally, doctors perform it on the day of admission.

The treatment of acute renal failure involves a series of measures, such as:

• Correction of reversible prerenal and postrenal causes
• Maintaining fluid and electrolyte balance
• Avoiding further nephrotoxic substances
• Adjusting medication dosages to account for kidney function
• Dialysis

In the short term, excessively high potassium levels pose a risk of cardiac arrest. Therefore, doctors must implement dietary measures to stop potassium intake (fruit juices and fruit).

The patient must avoid medications containing potassium or potassium-sparing diuretics. If necessary, doctors may prescribe a potassium binder.

There is also a risk of overhydration, which can lead to shortness of breath. However, since underhydration can also cause further kidney damage, sodium and fluid intake must be carefully balanced. The amount of fluid intake is determined by urine output and invisible fluid losses through the skin.

In cases of kidney failure, doctors must reduce the dosage of all water-soluble medications and those excreted by the kidneys. If this is not done, these medications accumulate in the blood and cause side effects and toxicity.

Typically, in cases of acute kidney failure, doctors discontinue ACE inhibitors, AT1 blockers, and nonsteroidal anti-inflammatory drugs (pain relievers), as they contribute to further deterioration. Contrast-enhanced imaging studies are also contraindicated.

If there is a critical increase in kidney toxins, doctors initiate renal replacement therapy. This is performed via hemodialysis. In cases of acute kidney failure, early initiation of dialysis (urea 150 mg/dl) and more intensive dialysis (daily dialysis) provide significant survival benefits.

Hemodialysis station @ Tyler Olson /AdobeStock

Acute kidney failure is a serious condition that patients and doctors often underestimate. Before the introduction of dialysis in 1960, the mortality rate was nearly 100 percent.

Today, the mortality rate for intensive care patients with acute kidney failure ranges from 40 to 70 percent. In most cases, kidney function recovers within 1 to 3 weeks.

Short-term prognosis:

Until a few years ago, doctors believed that once kidney failure had been overcome and kidney function had returned to normal, everything would be fine again. However, various studies have shown that the prognosis after kidney failure is not as good as previously assumed.

Patients who were already on dialysis have a 28-fold higher risk of developing chronic kidney failure requiring dialysis.

Long-term prognosis:

Acute kidney failure does not only affect the kidneys. Even after the kidneys have recovered, it leads to increased mortality in the long term. 

It appears that the kidneys “remember” acute kidney failure. Afterward, nothing is the same as before, even if creatinine levels are within the normal range.

Specialists are needed to care for patients with acute kidney failure.

Studies have shown that a nephrologist should be consulted as early as possible to prevent acute renal insufficiency. If renal failure does occur, the severity is less pronounced and mortality is lower.