Acute Kidney Injury

Acute kidney injury (AKI) is fairly common in hospitals. It affects about 1 in 10 to 1 in 7 hospitalised patients, and more than 1 in 2 patients in intensive care units (ICUs) (Ronco et al., 2019).

It occurs when the kidneys suddenly stop working properly, leading to a toxic buildup of urea and creatinine. Acute kidney injury can be life-threatening if not recognised and managed in a timely manner. This article will discuss the causes, symptoms, and stages of AKI to help you better understand this condition.

About Acute Kidney Injury

Acute kidney injury, formerly known as acute renal failure, is characterised by a sudden decline in kidney function [Goyal & Bashir, 2023]. The kidneys are crucial for filtering waste products from the blood, regulating fluid balance, and producing hormones that control blood pressure and red blood cell production. When the kidneys are damaged or unable to function properly, waste products can accumulate in the blood, leading to various complications.

Acute kidney injury can occur within hours or days [National Kidney Foundation, 2024]. Various factors, including pre-existing medical conditions, acute health events, and exposure to certain medications or substances, often trigger this rapid deterioration of kidney function. Understanding the causes and risk factors of acute kidney injury is essential for early detection and management.

Acute Kidney Injury (AKI) may not show clear symptoms in the early stages, and the signs can often be mild or overlooked. As the condition progresses, symptoms become more noticeable and may vary depending on the severity and underlying cause.

Some of the common early warning signs and symptoms include:

• Reduced urine output: Passing less urine than usual or, in severe cases, no urine at all
• Fatigue and weakness: Feeling unusually tired or lacking energy
• Loss of appetite: Reduced desire to eat or feeling unwell
• Fluid retention: Swelling in the legs, ankles, or feet due to fluid buildup
• Shortness of breath: Difficulty breathing, sometimes due to fluid accumulation in the lungs. If you experience sudden shortness of breath, seek emergency care immediately, as this could indicate pulmonary oedema (fluid in the lungs).
• Nausea and vomiting: Digestive discomfort along with decreased appetite
• Confusion or drowsiness: Changes in mental alertness, especially in severe cases
• Pain: Flank pain (pain on the side of the back), chest pain, or pressure

It is important to note that in some cases, acute kidney injury may not cause noticeable symptoms and is only detected through blood or urine tests. If you experience any of these signs, especially reduced urine output or swelling, seek medical attention promptly.

Acute kidney injury stages are mainly categorised into three groups based on the severity of kidney damage and the decrease in kidney function. These stages are primarily determined by an increase in serum creatinine levels (a waste product in the blood that the kidneys normally filter out) and a decrease in urine output.

• Stage I: Characterised by a 1.5-fold increase in serum creatinine or a reduction in urine output to less than 0.5 ml/kg/h for at least 6 hours. This stage represents mild kidney injury.
• Stage II: A 2-fold increase in serum creatinine or a reduction in urine output to less than 0.5 ml/kg/h for at least 12 hours, indicating moderate kidney injury.
• Stage III: Defined by a 3-fold increase in serum creatinine or a reduction in urine output to less than 0.5 ml/kg/h for at least 24 hours, signifying severe kidney injury. This stage often requires immediate hospitalisation and may need urgent treatment, including dialysis, to support kidney function.

Earlier, AKI was classified using the RIFLE criteria, but current practice follows the KDIGO staging system, which is now the international standard. 

KDIGO looks mainly at two things: changes in blood creatinine levels and how much urine the kidneys make. Based on this, AKI is divided into three stages – from mild (Stage 1) to severe (Stage 3). This system helps doctors decide on the best treatment and monitoring for each patient (National Kidney Foundation, 2024).

Understanding the stages of the disease is essential for determining the appropriate course of acute kidney injury treatment and monitoring the patient's progress.

Acute kidney injury can happen due to several reasons and often develops from a combination of factors. It is usually categorised into three main groups based on where the problem starts:

• Prerenal causes: These include conditions that reduce blood flow to the kidneys, leading to decreased kidney function. Examples include:
  • Dehydration
  • Blood loss or severe bleeding
  • Low blood pressure (hypotension)
  • Heart failure
  • Sepsis (overwhelming infection)
• Intrinsic renal causes: This category involves direct damage to the kidney tissue, impairing its ability to function properly. Common intrinsic renal causes include:
  • Acute tubular necrosis (ATN) due to prolonged lack of oxygen supply or exposure to toxins like certain medications, contrast dyes, or heavy metals
  • Glomerulonephritis (inflammation of the kidney's filtering units)
  • Interstitial nephritis (inflammation of the kidney's supporting tissue)
  • Vascular disorders affecting the blood vessels in the kidneys
• Postrenal causes: These encompass conditions that obstruct the flow of urine from the kidneys, leading to a buildup of waste products in the body. Examples include:
  • Kidney stones
  • Enlarged prostate gland
  • Tumours compressing the urinary tract
  • Bladder dysfunction or obstruction

Certain individuals are more susceptible to developing acute kidney injury due to various factors, including pre-existing medical conditions, age, and hospitalisation.

Those at a higher risk of acute kidney injury include:

• Hospitalised patients, especially those in critical care units, are at high risk due to the high prevalence of conditions that can lead to acute kidney injury, such as sepsis and major surgery.
• Patients with chronic kidney disease (CKD) are more vulnerable to further injury.
• Elderly patients are more prone due to age-related declines in kidney function and have a higher likelihood of comorbid conditions.
• Patients with diabetes and hypertension are at risk, as these conditions can exacerbate kidney damage and increase the risk of acute kidney injury.
• Individuals with certain medical conditions, such as multiple myeloma and vasculitis, and those undergoing major surgery or experiencing severe dehydration, haemorrhage, or severe skin burns.

Acute kidney injury can lead to several serious complications if not properly managed. The buildup of waste products in the blood due to impaired kidney function can affect other vital organs, such as the brain, heart, and lungs. It can also disrupt the body's ability to maintain the right balance of fluids and minerals, leading to conditions like:

• Hyperkalaemia (high potassium levels)
• Metabolic acidosis
• Fluid overload (oedema or pulmonary oedema)

Furthermore, experiencing an episode of acute kidney injury increases the risk of developing CKD and long-term kidney failure. The disease is also associated with an increased risk of cardiovascular events, including heart disease and stroke.

Preventing acute kidney injury involves several strategies, particularly for individuals at higher risk. Some of these strategies include:

• Patients with conditions such as diabetes, hypertension, CKD, heart failure, and liver disease should be closely monitored, especially when they become unwell or start new medications.
• Optimising haemodynamic and volume status by ensuring adequate fluid intake and maintaining optimal blood pressure can help prevent reduced blood flow to the kidneys, a common cause of acute kidney injury.
• Certain medications like non-steroidal anti-inflammatory drugs (NSAIDs), angiotensin-converting enzyme (ACE) inhibitors, and diuretics can exacerbate or cause acute kidney injury. These should be carefully managed or avoided if possible.
• Maintaining adequate fluid intake is crucial to prevent dehydration, which can lead to this condition, especially in patients who cannot maintain their fluid intake independently.
• Practising a healthy lifestyle, including regular exercise, a balanced diet low in sodium, and minimal alcohol consumption, can also help reduce the overall risk of developing the disease.

Diagnosing acute kidney injury involves a combination of physical examination, medical history review, and various tests. Some of the most common diagnostic methods include:

• Blood tests: Measuring creatinine levels and blood urea nitrogen (BUN) can help assess kidney function and determine the severity of the condition.
• Urine output monitoring: Decreased urine output is a common sign of acute kidney injury, and monitoring urine production can help in assessing the condition.
• Urine tests: Analysing urine samples for protein, blood, or other abnormalities can provide insights into kidney function and help identify the underlying cause of the condition.
• Imaging tests: Ultrasound, computed tomography (CT) scans, or magnetic resonance imaging (MRI) scans may be used to visualise the kidneys and identify any structural abnormalities or obstructions.
• Kidney biopsy: In some cases, a small sample of kidney tissue may be removed and examined under a microscope to determine the cause of the condition and assess the extent of damage.

The treatment of acute kidney injury focuses on supporting your body while the kidneys recover and addressing the underlying cause. This may include managing fluid levels, correcting imbalances in the blood, and treating any associated conditions such as infections or heart-related issues.

The exact approach can vary from person to person, depending on how severe the condition is, overall health, and how quickly symptoms are progressing. In many cases, early care and close monitoring can help prevent the condition from worsening.

Disclaimer: This information is for general awareness only and should not be considered medical advice. Acute kidney injury can become serious quickly, so always consult your doctor for proper diagnosis and treatment. Do not take or stop any medicine without medical guidance.

1. Conservative Management

A. Fluid Management

• Goal: 
  • Restore and maintain adequate fluid balance to ensure proper kidney perfusion.
• Intervention:
  • Isotonic fluids like normal saline are used for volume resuscitation in hypovolemic states.
  • Furosemide: A loop diuretic that promotes diuresis and helps manage volume overload in patients with kidney dysfunction.
  • Torsemide: Another potent loop diuretic that enhances fluid removal, especially in volume-overloaded patients.
  • Albumin: May be administered alongside diuretics in hypoalbuminemic patients to maintain oncotic pressure and enhance fluid mobilisation.

B. Electrolyte and Acid-Base Imbalance Management

• Hyperkalemia:
  • Calcium gluconate: Stabilises cardiac membranes to prevent arrhythmias in severe hyperkalemia.
  • Sodium polystyrene sulfonate: A potassium binder that promotes elimination of potassium through the gastrointestinal tract.
  • Patiromer: Binds to potassium in the colon, gradually lowering serum potassium levels.
  • Sodium zirconium cyclosilicate: Exchanges sodium for potassium in the intestines, aiding in potassium removal.
  • Insulin + Dextrose: This combination drives potassium into cells, resulting in a rapid reduction of serum potassium levels.
  • Salbutamol: A beta-agonist that promotes intracellular potassium shift, helping to lower serum potassium levels.
• Metabolic acidosis: 
  • Sodium bicarbonate: Used to correct significant acidemia by buffering excess hydrogen ions.
• Hyperphosphatemia: 
  • Sevelamer: A non-calcium phosphate binder that reduces phosphate absorption in the gut.
  • Calcium acetate: Binds dietary phosphate in the intestine to lower serum phosphate levels.
  • Lanthanum carbonate: Another phosphate binder that prevents phosphate absorption and is effective in CKD.
• Hypocalcemia (if symptomatic): 
  • Calcium gluconate: Administered intravenously to correct acute symptomatic hypocalcemia.
  • Calcium chloride: Used in more severe cases of hypocalcemia for rapid calcium replacement.

C. Medication Adjustment

• Nephrotoxic medications such as NSAIDs, aminoglycosides (e.g., gentamicin), vancomycin, ACE inhibitors, and ARBs may be paused or dose-adjusted.
• Drug dosing must be tailored to current renal function, considering the patient’s glomerular filtration rate (GFR) or serum creatinine levels.

D. Treating Underlying Causes

• Sepsis: 
  • Meropenem: A broad-spectrum carbapenem antibiotic used in severe infections to cover resistant organisms.
  • Ceftriaxone: A third-generation cephalosporin effective against a wide range of gram-positive and gram-negative bacteria.
• Heart failure: 
  • Diuretics: Help reduce fluid overload and relieve symptoms of congestion.
  • Nitroglycerin: A vasodilator that reduces preload and afterload, improving cardiac output.
  • Dobutamine: An inotrope that enhances cardiac contractility, especially useful in acute decompensated heart failure.
  • Obstruction: May require catheterisation, ureteral stenting, or surgical intervention.

2. Renal Replacement Therapy (Dialysis)

Dialysis is indicated for patients with severe AKI and complications such as refractory hyperkalemia, volume overload, severe acidosis, or uremic symptoms (e.g., encephalopathy, pericarditis).

• Haemodialysis (HD): Rapidly removes toxins and corrects electrolyte imbalances.
• Peritoneal Dialysis (PD): Used less commonly in AKI but may be considered in select patients, especially those with contraindications to HD.

3. Kidney Transplantation

While rare in AKI, transplantation may be considered if the injury leads to irreversible kidney damage and progresses to end-stage renal disease (ESRD).

It is important to be aware of the signs and symptoms that may indicate acute kidney injury so that prompt medical attention can be sought. Consult a doctor immediately if you experience any of the following:

• Reduced urine output: Producing little or no urine over a period of time
• Severe dehydration: Symptoms such as excessive vomiting, diarrhoea, or severe loss of blood
• Severe infections: Symptoms of sepsis, such as high fever, rapid breathing, and confusion
• Swelling in the legs, ankles, or feet
• Fatigue or shortness of breath
• Chest pain or pressure

• Acute kidney injury is a sudden decline in kidney function, leading to a buildup of waste products in the blood.
• It can be life-threatening if not promptly recognised and managed. 
• Various factors, including pre-existing medical conditions, acute health events, and exposure to certain medications or substances, often trigger it.
• It can be prevented by closely monitoring patients with pre-existing medical conditions such as diabetes, hypertension, or CKD, maintaining adequate fluid intake, and practising a healthy lifestyle, which includes regular exercise, a balanced diet low in sodium, and minimal alcohol consumption.