Acute Renal Failure (Acute Kidney Injury, AKI)
✅ Definition
Acute renal failure (ARF), now more commonly called acute kidney injury (AKI), is a
rapid decline in kidney function occurring over hours to days, resulting in:
- Impaired filtration of nitrogenous waste (↑ creatinine and BUN),
- Disturbance in fluid, electrolyte, and acid–base balance.
Etiology
1 Prerenal AKI
Decreased blood flow to the kidneys, but nephrons initially intact.
Causes:
- Volume loss: hemorrhage, vomiting, diarrhea, burns.
- Low cardiac output: heart failure, shock.
- Renal vasoconstriction: NSAIDs (↓ prostaglandins), ACE inhibitors (↓ efferent tone).
2 Intrinsic AKI
Direct injury to kidney structures:
- Tubular injury: Acute tubular necrosis (ischemic or nephrotoxic).
- Glomerular: Glomerulonephritis.
- Interstitial: Acute interstitial nephritis (e.g., drug- induced).
- Vascular: Vasculitis, malignant hypertension.
3 Postrenal AKI
Obstruction of urine flow leads to ↑ pressure → ↓ GFR.
Causes: BPH, ureteric stones, pelvic tumors, neurogenic bladder.
Pathogenesis
General Mechanism:
- Reduced GFR → ↓ excretion of nitrogenous wastes.
- Fluid and electrolyte imbalance: Na /K /H disturbances.
- Tubular dysfunction: impaired concentrating ability, urine abnormalities.
- Back-leak of filtrate (especially in acute tubular necrosis).
- Leads to azotemia, metabolic acidosis, hyperkalemia, and fluid overload.