Acute Kidney Injury

• Acute kidney injury ( AKI ) refers to a rapid drop in kidney function, diagnosed by measuring the serum creatinine .
• Acute kidney injury is most common in acutely unwell patients (e.g., infections or following surgery).
• The NICE guidelines (2019) criteria for diagnosing an acute kidney injury are: Rise in creatinine of more than 25 micromol/L in 48 hours Rise in creatinine of more than 50% in 7 days Urine output of less than 0.5 ml/kg/hour over at least 6 hours.
• Risk factors that would predispose to developing acute kidney injury include: Older age (e.g., above 65 years) Sepsis Chronic kidney disease Heart failure Diabetes Liver disease Cognitive impairment (leading to reduced fluid intake) Medications (e.g., NSAIDs, gentamicin, diuretics and ACE inhibitors) Radiocontrast agents (e.g., used during CT scans).
• Pre-renal causes of renal impairment are the most common.
• Insufficient blood supply ( hypoperfusion ) to kidneys reduces the filtration of blood.
• Pre-renal causes of renal impairment may be due to: Dehydration Shock (e.g., sepsis or acute blood loss) Heart failure.
• Renal causes of renal impairment are due to intrinsic disease in the kidney.
• Recovery usually takes 1-3 weeks.
• Management of acute kidney injury involves reversing the underlying cause and supportive management, for example, IV fluids for dehydration and hypovolaemia, withholding medications that may worsen the condition, and relieving the obstruction in a post-renal AKI.
• The epithelial cells can regenerate, making acute tubular necrosis reversible.
• Acute tubular necrosis refers to damage and death (necrosis) of the epithelial cells of the renal tubules and is the most common intrinsic cause of acute kidney injury.
• Leucocytes and nitrites suggest infection.
• Glucose suggests diabetes.
• Dialysis may be required in severe cases.
• Acute kidney injury is often preventable by avoiding nephrotoxic medications, ensuring adequate fluid intake, and additional fluids before and after radiocontrast agents.
• Complications of acute kidney injury include fluid overload, heart failure and pulmonary oedema, hyperkalaemia, metabolic acidosis, uraemia, which can lead to encephalopathy and pericarditis.
• Ultrasound of the urinary tract assesses for obstruction when a post-renal cause is suspected.
• Protein and blood suggest acute nephritis but can be positive in infection.
• Damage to the kidney cells occurs due to ischaemia due to hypoperfusion, nephrotoxins, or muddy brown casts on urinalysis confirm acute tubular necrosis.
• Urinalysis assesses for protein, blood, leucocytes, nitrites and glucose.