Acute kidney injury (AKI), previously known as acute renal failure, is an acute reduction in kidney function that can be reversed by immediate treatment. AKI is common among hospitalised patients, as it occurs in up to 7% of general ward admissions and almost 30% of intensive care unit patients.

Knowing the causes, recognising the signs, and starting treatment on time are essential to the patient’s recovery and the prevention of long-term complications. In this article, we will discuss the causes, symptoms, diagnosis, and treatments available for acute kidney injury.

Keep reading to learn more!

What is Acute Kidney Injury?

AKI is the sudden loss of kidney function to filter waste products from the bloodstream, resulting in a potentially life-threatening accumulation of toxins in the body. It is common in intensive care settings and, although it can be a terminal condition in serious cases, it is also potentially reversible, allowing patients to regain normal kidney function.

Acute kidney injury is an injury that causes the kidneys to lose the ability to excrete metabolic wastes from the blood. When the kidneys are unable to eliminate metabolic products, the levels of some wastes may rise to a harmful degree. The chemical composition of blood may also become unbalanced.

Most of the time, acute kidney injury occurs in the hospital, especially in patients needing intensive care. Acute kidney injury can range from mild to severe. If severe and left untreated, it can be life-threatening. However, with timely intervention, it is often reversible, and people who are otherwise healthy may regain normal or near-normal kidney function.

What are the Causes of Acute Kidney Injury?

AKI results from conditions that slow blood flow (prerenal), directly damage the kidney tissue (intrarenal), or block urine drainage (postrenal). Examples include dehydration (prerenal), glomerulonephritis or certain drugs (intrarenal), and kidney stones or an enlarged prostate (postrenal).

Acute kidney injury can occur when:

1. Blood flow to the kidneys is reduced.
2. The kidneys themselves are damaged.
3. Urine flow is blocked from the kidneys.

1. Reduced Blood Flow to the Kidneys (Prerenal Causes)

Diseases leading to the reduction of blood supply and possibly causing acute kidney injury are:

• Dehydration (loss of too much body fluid)
• Severe infections, with or without sepsis or septic shock
• Blood loss or fluid loss
• Low blood pressure caused by medications
• Heart attack, heart failure, or heart disease
• Liver cirrhosis or liver failure
• Severe allergic reactions (anaphylaxis)
• Major burns

2. Direct Kidney Damage (Intrinsic or Intrarenal Causes)

The possible causes of kidney damage may include:

• Inflammation of the kidney filters (glomerulonephritis)
• Certain medications, such as chemotherapy drugs, antibiotics, or imaging dyes
• Infections, including COVID-19
• Pollutants like alcohol, heavy metals, or cocaine
• Autoimmune diseases, e.g., lupus
• Blood clots in or around the kidneys
• Cholesterol plaques blocking the kidney’s blood flow
• Hemolytic uremic syndrome (destruction of red blood cells in the early stage)
• Rare conditions like scleroderma or thrombotic thrombocytopenic purpura
• Muscle breakdown (rhabdomyolysis) releases toxins
• Tumour lysis syndrome, which releases kidney-damaging toxins

3. Urine Flow Obstruction (Postrenal Causes)

Obstructions that prevent urine from leaving the body can cause AKI, including:

• Kidney stones
• Enlarged prostate
• Blood clots in the urinary tract
• Cancers: bladder, prostate, cervical, or colon
• Growths pressing on the ureters
• Nerve damage affecting bladder control

What are the Risk Factors of Acute Kidney Injury?

Risk of AKI is significantly increased by being hospitalised (especially in the ICU), advanced age, and having pre-existing conditions like diabetes, high blood pressure, heart failure, or peripheral artery disease. It almost always occurs alongside another serious medical event.

Acute kidney failure is a condition that rarely occurs without a medical condition or event. A situation that can put a person at risk of kidney failure includes the following diseases and conditions:

• Being in a hospital, especially when it is for a serious illness, and the condition requires the intensive care department, is stressful.
• Old age
• Having your blood vessels in your arms or legs blocked (peripheral artery disease)
• Diabetes
• High blood pressure
• Heart failure
• Kidney diseases
• Liver diseases
• Certain cancers and their treatments

What are the Symptoms of Acute Kidney Injury?

Symptoms vary, but often involve signs of fluid overload and waste retention. Common indicators are less urine output or none, swelling in the limbs, and systemic symptoms like fatigue, confusion, or shortness of breath.

The signs and symptoms of acute kidney injury can vary based on its cause, severity, and a person’s overall health. When they do appear, they may include one or more of the following:

• Making less urine (pee) than usual or no urine
• Swelling in legs, ankles, and/or feet
• Fatigue or tiredness
• Shortness of breath (trouble breathing)
• Confusion or mood changes
• High blood pressure
• Decreased appetite (low desire to eat)
• Nausea
• Flank pain (pain on the side of your back – between your ribs and hips)
• Chest pain or pressure
• Seizures or coma (in severe cases)

In some cases, AKI causes no symptoms and is only found through other tests done by your healthcare professional.

What is the Diagnosis of Acute Kidney Injury?

Diagnosis relies on blood tests to measure waste products and filtering capacity, including serum creatinine, eGFR, and BUN. A urinalysis checks for abnormalities, and imaging tests like an ultrasound may be used to identify structural blockages.

Some of the most common tests used to check for AKI include:

• Serum Creatinine: A blood test that measures the level of creatinine in the blood. It indicates how well the kidneys work. When they do not work properly, the serum creatinine level increases.
• eGFR (Estimated Glomerular Filtration Rate): This blood test measures the kidneys’ efficiency. eGFR is an approximate value that is calculated based on creatinine (a waste product filtered by the kidneys), age, and gender.
• BUN​‍​‌‍​‍‌​‍​‌‍​‍‌ (Blood Urea Nitrogen): Your blood urea nitrogen (BUN) level is determined from a test that measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that the body produces after breaking down protein. 

Healthy kidneys remove urea nitrogen from the blood. When the kidneys are not functioning properly, the BUN level is increased.

Besides that, the doctor may also order other blood tests, such as sodium, potassium, and bicarbonate level tests (to check if something is out of balance).

• Urine Output: During your hospital stay, the medical staff may record the amount of urine (pee) you produce per day.
• Urine Test (Urinalysis): This general urine test helps detect the presence of blood, protein, or other abnormal substances in the urine.
• Ultrasound: Imaging tests, like an ultrasound, may be helpful in some cases to check if stones or clots are affecting the kidney ​‍​‌‍​‍‌​‍​‌‍​‍‌function.

What are the Treatment Options for Acute Kidney Injury?

Treatment primarily involves a hospital stay focused on resolving the underlying cause of the kidney damage while managing complications until the kidneys recover. Management includes balancing fluids and electrolytes, correcting high potassium or low calcium, and using dialysis temporarily to filter blood if waste products are critical.

Treatment​‍​‌‍​‍‌​‍​‌‍​‍‌ of acute kidney injury is usually associated with admission to the hospital. The majority of those who suffer from AKI are patients in the hospital. The length of your hospital stay depends on the underlying cause of your acute kidney injury and how quickly your kidneys recover.

• Treating the Cause of Your Kidney Injury

First of all, the treatment of acute kidney injury requires identifying the disorder or injury that has damaged the kidneys. The treatment depends on the cause. The therapy might include discontinuing a drug that is harmful to your kidneys.

• Treating Complications until your Kidneys Recover

Your healthcare team works to support your kidneys and prevent complications as they recover. Key treatments may include:

• Treatments to balance your blood’s fluid levels. In case that reduced fluid in your blood is the reason for your acute kidney injury, you may be given fluids intravenously (IV).
• If acute kidney injury leads to fluid buildup, it can cause swelling in your arms and legs. In such cases, you may be prescribed diuretics, which help your body eliminate excess fluid.
• Medicines to control blood potassium. Your kidneys may not be able to remove potassium from your blood in the usual way. Potassium is one of the factors that regulate blood pressure and other body functions.

To prevent potassium buildup, you may be given drugs called potassium binders. They are sodium zirconium cyclosilicate (Lokelma) or patiromer (Veltassa). Excess potassium in the blood can cause irregular heartbeats (arrhythmias) and muscle weakness.

• Medicines to Restore Blood Calcium Levels: If your blood calcium drops too low, you may be given calcium intravenously (through a vein) to restore normal levels.
• Treatment to Remove Toxins from your Blood: If waste products accumulate in your blood, temporary hemodialysis (also called dialysis) may be needed. Dialysis helps remove toxins and excess fluids from your body while your kidneys recover.

Dialysis can also help remove excess potassium. During the procedure, a machine pumps blood out of your body through an artificial kidney, called a dialyser, which filters out waste before returning the cleansed blood to your body.

FAQs about Acute Kidney Injury

1. How to manage AKI at home?

Here’s how to manage AKI at home:

• Ask your doctor about your fluid intake.
• Eat a well-balanced diet.
• If you are started on dialysis, do as instructed and follow the dialysis schedule your doctor provides.
• Do not smoke.
• Limit alcohol consumption.
• Also, be sure to review all of your medicines with your doctor.

2. What are the 4 stages of AKI?

The typical course, which leads to the 4 stages of AKI, is as follows: (I) initiation, (II) oligo-anuria, (III) polyuria, and (IV) restitution. It is a dynamic process in which clinical signs of renal dysfunction appear in stage 2 (oligo-anuria).

3. What is another name for acute kidney injury?

Acute kidney injury (AKI) is also identified as acute renal failure (ARF) and acute kidney failure (AKF). These terms are used interchangeably to denote a sudden decrease in kidney function that occurs within a few hours or days.

4. Can drinking water help AKI?

If AKI is due to dehydration, it may be relieved by drinking more water. If you are severely dehydrated, you may receive fluids through an IV drip, which delivers them directly into a vein in your arm.

5. What to avoid with acute kidney injury?

Those with acute kidney injury are usually advised to avoid or limit foods high in sodium (salt), potassium, and phosphorus. A dietitian (food expert) can assist in meal planning to ensure you get the right amounts of each nutrient. In addition, it may be necessary to limit water and fluid intake per day.

Conclusion

Acute kidney injury is a condition that should not be taken lightly. It is, however, generally reversible and, therefore, requires timely detection and proper treatment. Knowing what causes it, recognising symptoms early, and seeking the right medical care can help a lot with recovery and prevent permanent kidney damage.

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