Acute Kidney Injury (AKI)

• Definition: Rapid drop in kidney function, diagnosed by measuring serum creatinine.
• Common in: Acutely unwell patients (e.g., infections, post-surgery).

Diagnosis Criteria (NICE Guidelines 2019)

• Rise in creatinine > 25 micromol/L in 48 hours.
• Rise in creatinine > 50% in 7 days.
• Urine output < 0.5 ml/kg/hour over at least 6 hours.

Risk Factors

• Older age (>65 years).
• Sepsis.
• Chronic kidney disease.
• Heart failure.
• Diabetes.
• Liver disease.
• Cognitive impairment.
• Medications: NSAIDs, gentamicin, diuretics, ACE inhibitors.
• Radiocontrast agents.

Causes of AKI

• Pre-renal (most common):
  • Insufficient blood supply (hypoperfusion).
  • Dehydration, shock, heart failure.
• Renal:
  • Intrinsic kidney diseases: Acute tubular necrosis, glomerulonephritis, etc.
• Post-renal:
  • Obstruction in urine outflow: Kidney stones, tumors, strictures, etc.

Acute Tubular Necrosis

• Definition: Damage and necrosis of renal tubular epithelial cells.
• Causes:
  • Ischaemia due to hypoperfusion (dehydration, shock, heart failure).
  • Nephrotoxins (gentamicin, radiocontrast agents).
• Diagnosis: Muddy brown casts on urinalysis.
• Prognosis: Reversible, recovery in 1-3 weeks.

Acute Interstitial Nephritis (AIN)

• Definition: Acute inflammation of the renal interstitium.
• Causes: Immune reaction due to drugs, infections, autoimmune conditions.
• Symptoms: Rash, fever, flank pain, eosinophilia.
• Management: Treat underlying cause, possibly use steroids.

Investigations

• Urinalysis: Checks for protein, blood, leucocytes, nitrites, glucose.
  • Leucocytes/nitrites: Infection.
  • Protein/blood: Acute nephritis.
  • Glucose: Diabetes.
• Ultrasound: Assess for obstruction.

Management

• Prevention:
  • Avoid nephrotoxic medications.
  • Ensure adequate fluid intake.
  • Fluids before/after radiocontrast agents.
• Treatment:
  • Reverse underlying cause.
  • Supportive management: IV fluids, withholding/adjusting medications, relieving obstruction.
  • Dialysis in severe cases.
• Specialist Input: Required in severe cases, unsure cause, or complications.

Complications

• Fluid overload, heart failure, pulmonary oedema.
• Hyperkalaemia.
• Metabolic acidosis.
• Uraemia: Can lead to encephalopathy, pericarditis.

Additional Resources

• Zero to Finals Members Area for quizzes and study tools.

Last updated: September 2023