28/11/2025
What is Acute Kidney Injury (AKI)?
AKI = a sudden drop in kidney function.
The kidneys cannot filter waste, balance fluids, or control electrolytes properly.
This happens over hours to days and is a medical emergency.
When the kidneys slow down, waste builds up, fluid accumulates, and electrolytes like potassium become dangerous.
If not treated quickly, AKI can lead to organ failure.
• ↓ GFR → ↓ urine output → waste accumulation → electrolyte imbalance → acidosis
• Hyperkalaemia is most dangerous (risk of cardiac arrest)
Risk Factors:
• Elderly
• Critically ill patients
• Dehydration
• Sepsis
• Nephrotoxic drugs
Laboratory Clues:
• ↑ Serum creatinine & BUN
• ↑ K⁺, ↓ Na⁺
• FeNa >2% (intrarenal)
• Urinalysis: muddy brown casts, tubular epithelial cells. Oliguria + rising creatinine + hyperkalaemia → act fast!
Types of AKI
AKI has three main causes:
1. Prerenal AKI (Most common)
Problem: Poor blood flow to the kidneys
• Dehydration
• Bleeding
• Sepsis
• Heart failure
• Low blood pressure
Kidneys are normal, but not receiving enough blood.
2. Intrarenal AKI
Problem: Damage inside the kidney
• Acute Tubular Necrosis (ATN)
• Nephrotoxic drugs (NSAIDs, aminoglycosides)
• Contrast dye
• Glomerulonephritis
• Infection
Kidney tissues are injured.
3. Postrenal AKI
Problem: Obstruction in the urinary system
• Enlarged prostate
• Kidney stones
• Tumours
• Blocked catheters
Urine cannot drain → pressure backs up into the kidneys.
Why Urine Output Drops in AKI
Urine drops because:
• Blood flow is reduced (prerenal)
• The kidney tubules are damaged (intrarenal)
• Urine is blocked from leaving (postrenal)
When kidneys cannot filter blood properly:
→ Less urine is produced
→ Waste builds up
→ Fluid accumulates in the body
→ Electrolytes become abnormal
Oliguria =