Acute Kidney Injury (AKI)

Acute Kidney Injury: Definition, Causes, Symptoms, Stages, Diagnosis, Treatment and Prevention

Acute kidney injury (AKI), also known as acute renal injury (ARI), is a sudden decrease in kidney function that can occur over a period of hours or days. It is a common condition that affects both hospitalized and non-hospitalized patients and can be caused by a variety of factors, including dehydration, kidney damage, infections, and medications.

Causes of Acute Kidney Injury

Acute kidney injury can occur due to various factors, including decreased blood flow to the kidneys, damage to the kidneys themselves, and obstruction of the urinary tract. 

1.) Dehydration: Dehydration is a common cause of AKI, especially in people who have lost a significant amount of fluids due to vomiting, diarrhea, excessive sweating, or insufficient intake of fluids. When the body is dehydrated, the kidneys may not receive enough blood flow to function properly, leading to AKI.

2.) Medications: Certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, and chemotherapy drugs, can damage the kidneys and cause AKI. The risk of AKI increases with high doses or prolonged use of these medications.

3.) Infection: Severe infections, such as sepsis, can cause AKI by reducing blood flow to the kidneys and damaging kidney tissue.

4.) Obstruction: Blockages in the urinary tract, such as kidney stones, tumors, or enlarged prostate gland, can cause AKI by preventing urine from flowing out of the kidneys and causing pressure buildup.

5.) Trauma: Traumatic injuries, such as those caused by car accidents, falls, or sports injuries, can damage the kidneys and cause AKI.

6.) Autoimmune disorders: Autoimmune disorders, such as lupus or vasculitis, can cause inflammation and damage to the blood vessels in the kidneys, leading to AKI.

7.) Heart failure: Severe heart failure can cause AKI by reducing blood flow to the kidneys and causing fluid buildup in the body.

8.) Liver disease: Advanced liver disease, such as cirrhosis, can cause AKI by reducing blood flow to the kidneys and impairing their ability to filter waste products from the blood.

9.) Contrast dye: Contrast dye used in imaging tests such as CT scans, MRIs, or angiograms, can sometimes cause AKI in people with pre-existing kidney problems.

In addition to these causes, AKI can also result from other factors such as exposure to toxins or chemicals, blood loss, or low blood pressure. The severity of AKI can range from mild to severe, and prompt medical attention is necessary to prevent further complications.

Categories of Acute Kidney Injury: Pre-Renal, Renal Parenchymal, Post-Renal 

Acute Kidney Injury (AKI) can be classified into three categories: Pre-renal AKI, Renal Parenchymal AKI, and Post-renal AKI. Each of these categories has unique causes, pathophysiology, and management strategies.

Pre-Renal AKI

Pre-renal AKI refers to a condition where there is a decrease in renal perfusion, resulting in a decrease in glomerular filtration rate (GFR). This can be caused by conditions that lead to decreased blood flow to the kidneys, such as hypovolemia, dehydration, decreased cardiac output, or decreased peripheral vascular resistance. 

The decrease in renal perfusion activates the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS), leading to vasoconstriction of the renal arteries and a decrease in GFR. Treatment of Pre-renal AKI involves restoring renal perfusion by correcting the underlying cause. 

This may include fluid resuscitation, blood transfusions, or medications to improve cardiac output or peripheral vascular resistance.

Renal Parenchymal AKI

Renal Parenchymal AKI refers to a condition where there is damage to the renal parenchyma, including the glomeruli, tubules, and interstitium. This can be caused by a variety of factors, including ischemia, toxins, infections, and inflammation. 

The damage to the renal parenchyma results in a decrease in GFR and impaired renal function. Treatment of Renal Parenchymal AKI involves identifying and treating the underlying cause, as well as supportive measures such as renal replacement therapy (RRT), fluid and electrolyte management, and medication adjustments.

Post-renal AKI

Post-renal AKI refers to a condition where there is an obstruction to urine flow from the kidneys to the bladder or from the bladder to the urethra. This can be caused by a variety of factors, including kidney stones, tumors, prostate enlargement, or neurogenic bladder. 

The obstruction causes an increase in pressure within the renal collecting system, resulting in a decrease in GFR and impaired renal function. Treatment of Post-renal AKI involves removing the obstruction through procedures such as ureteral stent placement, nephrostomy tube placement, or surgical intervention. Once the obstruction is relieved, renal function typically returns to normal.

Stages of Acute Kidney Injury

Acute Kidney Injury (AKI) can be classified into stages based on changes in serum creatinine levels and urine output. The most commonly used classification systems are the AKIN (Acute Kidney Injury Network) and KDIGO (Kidney Disease: Improving Global Outcomes) criteria.

AKIN (Acute Kidney Injury Network)

The AKIN criteria classify AKI into three stages based on the severity of the condition:

Stage 1: Serum creatinine level increased by ≥ 0.3 mg/dL (26.4 μmol/L) or by 1.5 to 1.9 times baseline within 48 hours, or urine output < 0.5 mL/kg/h for 6 to 12 hours.

Stage 2: Serum creatinine level increased by 2.0 to 2.9 times baseline within 48 hours, or urine output < 0.5 mL/kg/h for ≥ 12 hours.

Stage 3: Serum creatinine level increased by ≥ 3.0 times baseline within 48 hours, or serum creatinine level ≥ 4.0 mg/dL (353.6 μmol/L) with an acute increase of at least 0.5 mg/dL (44.2 μmol/L), or urine output < 0.3 mL/kg/h for ≥ 24 hours, or anuria for ≥ 12 hours.

KDIGO (Kidney Disease: Improving Global Outcomes)

The KDIGO criteria classify AKI into three stages based on changes in serum creatinine levels and urine output:

Stage 1: Serum creatinine level increased by ≥ 0.3 mg/dL (26.4 μmol/L) or by 1.5 to 1.9 times baseline within 7 days, or urine output < 0.5 mL/kg/h for 6 to 12 hours.

Stage 2: Serum creatinine level increased by 2.0 to 2.9 times baseline within 7 days, or urine output < 0.5 mL/kg/h for ≥ 12 hours.

Stage 3: Serum creatinine level increased by ≥ 3.0 times baseline within 7 days, or serum creatinine level ≥ 4.0 mg/dL (353.6 μmol/L) with an acute increase of at least 0.5 mg/dL (44.2 μmol/L), or urine output < 0.3 mL/kg/h for ≥ 24 hours, or anuria for ≥ 12 hours, or the initiation of RRT (renal replacement therapy).

Symptoms of Acute Kidney Injury (AKI)

The symptoms of acute renal injury can vary depending on the underlying cause and the severity of the condition. Common symptoms include:

1.) Decreased urine output: One of the earliest signs of AKI is a decrease in urine output. This can be noticed as a reduced frequency of urination or decreased volume of urine passed.

2.) Fluid retention: As the kidneys are unable to remove excess fluid from the body, it can lead to fluid retention causing swelling in the legs, ankles, feet, face, or abdomen. This is also known as edema. 

3.) Fatigue: A feeling of tiredness and lethargy is common in patients with AKI. This may be due to the buildup of waste products in the body or electrolyte imbalances.

4.) Shortness of breath: As fluid accumulates in the lungs due to fluid overload, it can cause difficulty breathing, coughing, or chest pain.

5.) Nausea and vomiting: AKI can cause nausea, vomiting, and a loss of appetite due to the accumulation of waste products in the body.

6.) Confusion: As AKI progresses, it can cause confusion, delirium, or seizures due to the buildup of toxins in the body affecting the brain.

7.) Irregular heartbeats: Changes in electrolyte levels caused by AKI can affect the heart rhythm, leading to palpitations, irregular heartbeats, or even cardiac arrest.

It is important to note that some people with AKI may not experience any symptoms until kidney function has significantly declined. Therefore, it is important to seek medical attention if you are at risk for AKI, such as if you have a history of kidney disease or are taking medications that can affect kidney function.

Complications of Acute Renal Injury

Acute kidney injury (AKI) can lead to several complications, especially if left untreated or poorly managed. 

Here are some of the common complications associated with AKI:

Chronic Kidney Disease

AKI can lead to permanent damage to the kidneys, resulting in chronic kidney disease (CKD). Patients with AKI are at an increased risk of developing CKD, which can progress to end-stage renal disease (ESRD) requiring dialysis or kidney transplantation.

Electrolyte Imbalances

The kidneys play a vital role in maintaining electrolyte balance in the body. AKI can cause imbalances in electrolytes such as potassium, sodium, and calcium, which can lead to serious complications such as cardiac arrhythmias or seizures.

Acid-Base Imbalances

AKI can cause a buildup of acids in the body, leading to a condition called metabolic acidosis. Symptoms of metabolic acidosis can include fatigue, rapid breathing, and confusion.

Uremic Syndrome

AKI can cause a buildup of waste products in the blood, leading to a condition called uremic syndrome. This can cause symptoms such as nausea, vomiting, loss of appetite, confusion, and seizures.

Volume Overload 

 AKI can lead to fluid buildup in the body, which can cause swelling in the legs or feet, shortness of breath, and high blood pressure. This is because the kidneys are responsible for regulating fluid balance in the body, and when they are not functioning properly, excess fluid can accumulate.

Infections

AKI can increase the risk of infections, particularly urinary tract infections (UTIs) and sepsis. This is because the kidneys play a role in filtering out bacteria and other pathogens from the blood.

Bleeding

AKI can cause bleeding due to impaired platelet function or decreased levels of clotting factors.

Cardiovascular Complications

AKI can increase the risk of cardiovascular complications, such as heart attack and stroke, due to changes in blood pressure and electrolyte imbalances.

Mortality

In severe cases, AKI can lead to multi-organ failure and death.

It is important to note that the risk of complications varies depending on the severity and duration of AKI, as well as the presence of underlying medical conditions. Early detection and appropriate management of AKI can reduce the risk of complications and improve the chances of recovery. 

Diagnosis of Acute Kidney Injury

The diagnosis of acute kidney injury (AKI) typically involves a combination of clinical assessment, laboratory tests, and imaging studies. Here are some of the common methods used to diagnose AKI:

History and physical exam

The doctor will ask about your medical history and symptoms and perform a physical examination to check for signs of AKI such as swelling, decreased urine output, or abnormal fluid levels in the body.

Urine tests

A urine test can help determine if there is blood, protein, or other abnormalities in the urine. This can help identify the underlying cause of AKI.

Blood tests

Blood tests can measure the level of creatinine, a waste product that builds up in the blood when the kidneys are not functioning properly. An increase in creatinine levels can indicate AKI. Other blood tests may also be ordered to check for electrolyte imbalances or other abnormalities.

Imaging studies

Imaging studies such as ultrasound, CT scan, or MRI can help identify any structural abnormalities in the kidneys, urinary tract, or other organs that may be causing AKI.

Kidney biopsy

In some cases, a kidney biopsy may be recommended to help determine the underlying cause of AKI. This involves taking a small sample of kidney tissue for examination under a microscope.

The diagnosis of AKI can be challenging, as the symptoms may be non-specific and may overlap with other medical conditions.

Treatment for Acute Kidney Injury

The treatment of Acute Kidney Injury (AKI) depends on the underlying cause of the condition and the stage of AKI. The main goals of treatment are to prevent further kidney damage, support the remaining kidney function, and address any complications that may arise. 

Some of the treatment options for AKI are:

A.) Treating the underlying cause

Acute kidney injury can be caused by a wide range of conditions, such as dehydration, infections, medication toxicity, and blood loss. Treatment of the underlying condition can help prevent further kidney damage and improve kidney function.

B.) Fluid Management

Adequate hydration is crucial for kidney function, and in some cases, fluid therapy may be necessary to support kidney function. On the other hand, excessive fluid intake can lead to fluid overload and worsen acute kidney injury.

C.) Electrolyte Management

Electrolyte imbalances, such as high potassium levels, can cause further kidney damage and other complications. Treatment may involve medications or other interventions to regulate electrolyte levels.

D.) Medications

Some medications may be used to manage complications of acute kidney injury, such as high blood pressure or anemia. However, some medications can also cause or worsen acute kidney injury, and caution should be taken in their use. Some of the medications used in the treatment of acute kidney injury are: 

1.) Diuretics: Diuretics are medications that help remove excess fluid from the body by increasing urine production. They may be used to manage fluid overload in patients with AKI.

2.) Anti-hypertensives: High blood pressure is a common complication of AKI and medications that lower blood pressure may be used to manage this condition.

3.) Medications to manage electrolyte imbalances: Medications such as sodium bicarbonate, insulin, and calcium may be used to manage electrolyte imbalances such as high potassium levels.

4.) Medications to manage acidosis: Acidosis is a condition where the blood becomes too acidic, which can worsen AKI. Medications such as sodium bicarbonate may be used to manage acidosis.

5.) Medications to manage anemia: Anemia is a common complication of AKI, and medications such as erythropoietin may be used to manage this condition.

6.) Antibiotics: Antibiotics may be used to treat infections that may be causing or contributing to AKI.

It is important to note that the use of medications in AKI is tailored to the individual patient's needs and clinical status, and should be taken under the supervision of a healthcare professional who has expertise in kidney disease management. Additionally, some medications can cause or worsen AKI, and caution should be taken in their use.

E.) Nutritional Support

Acute kidney injury can affect the body's ability to absorb and utilize nutrients, and some patients may require nutritional support to maintain their health and support kidney function.

F.) Dialysis

Dialysis may be necessary in severe cases of acute kidney injury to help remove waste products from the blood and support kidney function.

Read more: What is Dialysis?

G.) Monitoring and Follow-up

Patients with acute kidney injury require close monitoring of urine output, electrolyte levels, and other parameters. Follow-up with a healthcare provider may be necessary to monitor kidney function and manage any ongoing complications.

H.) Renal Replacement Therapy (RRT)

In severe cases of acute kidney injury, RRT may be necessary to replace the lost kidney function. RRT can be done through dialysis, which removes waste products and excess fluid from the blood, or through kidney transplantation.

It is important to note that the management of acute kidney injury should be tailored to the individual patient's needs and clinical status, and should be performed under the supervision of a healthcare professional with expertise in kidney disease management.

Prevention of Acute Kidney Injury

There are several steps you can take to reduce the risk of developing acute renal injury:

General Prevention Strategies

Several general strategies can help prevent AKI:

Stay Hydrated

Maintaining good hydration is key to preventing AKI caused by prerenal factors such as dehydration. Drinking enough water and other fluids is important, especially during times of illness or when participating in strenuous activity.

Avoid Nephrotoxic Medications

Certain medications can be toxic to the kidneys and can cause AKI, especially when taken in large doses or when there is an underlying kidney problem. It is important to avoid these medications whenever possible or to use them under the guidance of a healthcare provider.

Monitor Kidney Function

People with pre-existing kidney disease or other conditions that increase the risk of AKI should have their kidney function monitored regularly.

Practice Good Hygiene

Practicing good hygiene, such as washing your hands regularly and avoiding contact with people who are sick, can help reduce the risk of infections that can cause AKI.

Specific Prevention Strategies

In addition to general prevention strategies, there are specific measures that can be taken to prevent AKI in high-risk populations:

1.) Hospitalized patients: 

Hospitalized patients are at increased risk for AKI due to factors such as underlying medical conditions, surgical procedures, and exposure to nephrotoxic medications. To prevent AKI in hospitalized patients, healthcare providers can monitor kidney function closely, avoid nephrotoxic medications whenever possible, and ensure appropriate hydration.

2.) Patients with pre-existing kidney disease: 

Patients with pre-existing kidney disease are at increased risk for AKI due to the already-compromised function of their kidneys. To prevent AKI in these patients, healthcare providers can monitor kidney function closely, avoid nephrotoxic medications, and manage underlying medical conditions.

3.) Patients undergoing contrast imaging: 

Contrast dyes used in imaging tests can be nephrotoxic and can cause AKI, especially in patients with pre-existing kidney disease. To prevent AKI in these patients, healthcare providers can use alternative imaging methods whenever possible or take steps to minimize the amount of contrast dye used.

Preventing AKI is an important goal that can help avoid serious kidney damage and long-term consequences. By staying hydrated, avoiding nephrotoxic medications, managing medical conditions, avoiding kidney injury, and taking specific prevention measures for high-risk populations, we can work to reduce the incidence of acute kidney injury and improve outcomes.

Prognosis of Acute Kidney Injury

The prognosis of AKI can depend on the severity of the condition, the underlying cause, and the timeliness and effectiveness of treatment.

The prognosis of AKI can be affected by several factors, including:

1.) The severity of AKI: The severity of AKI is classified into three stages - Stage 1, Stage 2, and Stage 3. Stage 1 is the mildest form, while Stage 3 is the most severe. The prognosis of AKI is worse for patients in Stage 3.

2.) Underlying Cause: The underlying cause of AKI can also affect the prognosis. For example, AKI caused by dehydration or medication toxicity is typically more easily reversible than AKI caused by severe infections or trauma.

3.) Co-existing medical conditions: Patients with co-existing medical conditions such as heart failure or liver disease may have a worse prognosis due to the increased likelihood of complications.

4.) Timeliness of Treatment: Early and prompt treatment of AKI can improve the prognosis by preventing further kidney damage and allowing for the recovery of kidney function.

In general, patients with mild to moderate AKI have a good prognosis and are likely to recover normal kidney function within a few weeks to months. However, patients with severe AKI, especially those in Stage 3, may require long-term or even lifelong dialysis. Additionally, patients with underlying medical conditions or who experience complications such as sepsis or multi-organ failure may have a worse prognosis.