Acute Kidney Injury (AKI): Understanding The Basics

Kidneys are one of the most important organs in our body. They remove excess fluids, salt, and waste materials from the blood for elimination in the urine. Every day, they filter about 200 litres of blood to produce approximately 2 litres of urine. Acute kidney injury (AKI), also known as acute renal failure, refers to a condition where the kidneys suddenly lose this ability to filter and excrete waste from blood, usually developing within hours to a few days.

The resultant accumulation of waste products can rapidly damage your brain, lung, and heart function, and can be life-threatening. It is common in patients who are in the hospital, in intensive care units, especially in older adults and those with chronic, poorly controlled medical conditions (e.g. morbid obesity, diabetes, high blood pressure, liver disease, heart failure)

How common is acute kidney injury?

In a recent survey published in 2016, the incidence of AKI has been identified as 19.4% in Eastern Asia, 7.5% in Southern Asia, 31.0% in South-eastern Asia, 9.0% in Central Asia, and 16.7% in Western Asia. Overall, 21.6% of adults and 33.7% children experienced AKI worldwide.

Symptoms of acute kidney injury

• Little urine production 
• Shortness of breath
• Swelling in ankles, legs, and around the eyes (oedema)
• Confusion
• Fatigue
• Nausea
• Chest pain or pressure
• Seizures or coma in severe cases

In some cases, AKI does not present with symptoms and is only found through medical tests for other purposes. 

Causes of acute kidney injury

AKI could be caused by many underlying conditions, which can be broadly classified into pre-renal, renal, and post-renal. 

Pre-renal causes are conditions which reduce blood perfusion to kidneys: 

• Haemorrhage – trauma or menstruation-induced blood loss could lead to decreased blood volume.
• Fluid loss from burns, severe diarrhoea or dehydration
• Heart failure or heart attack could dramatically decrease blood supply to kidneys. 
• Low blood pressure or hypotension
• Excessive use of NSAIDs (non-steroidal anti-inflammatory drugs) e.g. aspirin, ibuprofen and naproxen for relief of headache, pain and swelling 

Renal causes involve direct damage within kidneys:

• Inflammation or damage to kidney tubules (e.g. glomerulonephritis, vasculitis or interstitial nephritis) due to 
  • Bacterial infections
  • Exposure to toxins (heavy metals, smoke, cocaine and alcohol)  
  • Adverse reactions to medication (chemotherapy, antibiotics, ibuprofen)
  • Other diseases e.g. multiple myeloma (a type of cancer) or scleroderma (connective tissue disorder)

Post-renal causes refer to blockage of urinary tract which obstructs flow of urine out of kidneys:

• Bladder or cervical cancer 
• Inflammation of bladder or urinary tract from infections
• Enlarged prostate (male only)
• Kidney stones or kidney sands: high blood calcium level could predispose to stone formation
• Blood clots in kidney blood vessels
• Problems with the nervous system that affect the bladder and urination

Clinical diagnosis

• Urine tests: Measurement of urine output, as well as analysing urine (urinalysis) for signs of kidney failure (e.g. excessive protein in urine)
• Blood tests: Derangements in levels of creatinine, urea nitrogen phosphorus, potassium are indications of kidney injury.
• Estimated glomerular filtration rate (eGFR) may be derived from your blood creatinine level test, age, body size and gender. This can reveal the extent of the decline in kidney function.
• Ultrasound: the most convenient way of visualising your kidney directly to look for site of injury.
• Kidney biopsy: in some cases, a tiny piece of your kidney tissue will be removed with a needle and studied under microscope to determine the cause of kidney injury. 

Treatment

Treatment of AKI varies depending on the cause. Most of the treatment happens in a hospital setting till patient regains partial kidney function. Some general treatment include:

• IV fluids: replenish blood volume if needed
• Diuresis: use of medications called diuretics to help kidneys eliminate excess fluids
• Medications to control blood potassium: in AKI, kidney loses its ability to remove excess potassium from blood, which could potentially result in fatal cardiac arrest. 
• Antibiotics to treat or prevent infections
• Dialysis: when kidneys fail and cannot get rid of waste substances in your blood, dialysis is needed to artificially remove them. This will likely only be temporary.

Prevention

• Stop smoking: cigarette smoke is one of the most significant toxins contributing to kidney injuries
• Drink in moderation: excessive alcohol is toxic to the kidneys
• Eat a healthy diet low in salt and fat
• Do a minimum of 30 minutes exercise at least 5 days a week 
• Follow medical advice: if you have diabetes or cardiovascular disease, work with your doctor to manage these conditions well as they can lead to AKI. 
• Be careful with drug combinations: when taking over-the-counter medications, it is important to consult your pharmacist or doctor. Some combinations could result in fatal AKI, especially with over-the-counter NSAIDs