Acute Kidney Injury

Acute kidney injury is a serious condition that affects millions of people worldwide. It occurs when the kidneys suddenly stop working properly, leading to a rapid accumulation of waste products in the blood. Acute kidney injury can be life-threatening if not recognised and managed timely. This article will discuss the causes, symptoms, and stages of acute renal failure 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. 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. 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 acute kidney injury's causes and risk factors is essential for early detection and management.

The early signs of acute kidney failure may be subtle and easily overlooked. However, recognising these signs can help you seek timely treatment and prevent the condition from worsening.

Some of the early signs of acute kidney failure include:

• Reduced urine output

• Fatigue

• Decreased appetite

• Swelling in your legs, ankles, or feet

• Pain on the side of your back

AKI symptoms can vary depending on the severity and underlying cause of the condition. Some common AKI symptoms include:

• Reduced urine output: Making less urine (pee) than usual or no urine at all.

• Fluid retention: Swelling in the legs, ankles, and/or feet due to fluid buildup.

• General illness: Feeling weak and tired and experiencing fatigue.

• Gastrointestinal symptoms: Nausea, vomiting, and decreased appetite.

• Respiratory issues: Shortness of breath (trouble breathing), which can be due to fluid accumulation in the lungs.

• Neurological symptoms: Confusion, drowsiness, seizures, and coma in severe cases.

• Pain: Flank pain (pain on the side of your back—between your ribs and hips), chest pain, or pressure.

It is important to note that in some cases, acute kidney injury may not cause noticeable symptoms and is only discovered through laboratory tests performed for other reasons. If you experience any of these symptoms, especially if you have a history of kidney disease or other risk factors, it is essential to seek medical attention promptly.

Acute kidney injury stages are mainly categorised into three groups based on the severity of kidney damage and the level of decrease in kidney function. These stages are primarily determined by an increase in serum creatinine levels 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: There is 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 0.3 ml/kg/h for at least 24 hours, signifying severe kidney injury.

It's crucial to note that the RIFLE criteria further classify acute kidney injury into risk (R), injury (I), failure (F), loss (L), and end-stage renal disease (E), providing a more detailed assessment of kidney dysfunction. 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 pathophysiology is complex and multifactorial. It can result from a variety of causes, which are typically categorised into three main groups:

1. Prerenal causes: These include conditions that reduce blood flow to the kidneys, leading to decreased kidney function. Prerenal causes are the most common, accounting for approximately 60–70% of all cases. Examples include:

   • Dehydration

   • Blood loss or severe bleeding

   • Low blood pressure (hypotension)

   • Heart failure

   • Sepsis (overwhelming infection)

2. 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

3. Postrenal causes: These encompass conditions that obstruct the flow of urine from the kidneys, leading to a buildup of waste products in the body. Postrenal causes are the least common, accounting for around 5–10% of all cases. 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, 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), as their pre-existing kidney damage makes them more vulnerable to further injury.

• Elderly patients, who are more prone due to age-related declines in kidney function and have a higher likelihood of comorbid conditions.

• Patients with diabetes and hypertension, 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 levels of creatinine and blood urea nitrogen (BUN) can help assess kidney function and determine the severity of the disease.

• Urine output monitoring: Decreased urine output is a common sign of acute kidney failure, and monitoring urine production can help diagnose the condition.

• Urine tests: Analysing urine samples for the presence of protein, blood, or other abnormalities can provide insights into kidney function and help identify the underlying cause of the disease.

• 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.

Acute kidney injury treatments depend on the underlying cause and the severity of the condition. Some common treatment options include:

1. Conservative management

   • Fluid management: Ensuring adequate hydration and carefully monitoring fluid intake and output can help maintain proper fluid balance in the body.

   • Medication adjustment: Doctors may need to adjust or temporarily discontinue medications that can potentially harm the kidneys, such as NSAIDs or certain antibiotics.

   • Treating underlying conditions: Addressing the underlying cause of acute kidney injury, such as sepsis or heart failure, is crucial for promoting kidney recovery.

2. Dialysis: In severe cases of acute kidney injury, dialysis may be necessary to support kidney function and remove waste products from the blood. There are two main types of dialysis:

   • Haemodialysis: Blood is filtered through a machine to remove waste products and excess fluid before being returned to the body.

   • Peritoneal dialysis: A special solution is introduced into the abdominal cavity, where it absorbs waste products and excess fluid from the blood. The solution is then drained and replaced periodically.

3. Kidney transplantation: In rare cases where acute kidney injury leads to permanent kidney failure, a kidney transplant may be necessary. This involves surgically replacing the damaged kidney with a healthy one from a donor.

The goal of acute kidney injury treatment is to support the kidneys, prevent further damage, and promote recovery. With prompt and appropriate treatment, many patients can regain normal kidney function. However, some may experience long-term complications or progress to CKD, emphasising the importance of early detection and intervention.

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.