Acute Kidney Injury

Definition & Staging - Kidney Crisis Code

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Etiology - AKI's Usual Suspects

• Prerenal (↓ Perfusion):
  • Hypovolemia: Hemorrhage, dehydration, burns
  • ↓ Effective volume: CHF, cirrhosis, sepsis/shock
  • Drugs: NSAIDs, ACEi/ARBs
  • Renal Artery Stenosis
• Intrinsic Renal (Parenchymal Damage):
  • ATN (most common): Ischemic; Nephrotoxic (contrast, aminoglycosides, amphotericin B, rhabdomyolysis)
  • AIN: Drugs (antibiotics, NSAIDs, PPIs), infections, autoimmune
  • Glomerulonephritis (e.g., RPGN)
  • Vascular: HUS, TTP, vasculitis, malignant HTN
• Postrenal (Obstruction):
  • Ureteric/Bladder neck/Urethral: BPH, stones, tumors, strictures

⭐ Acute Tubular Necrosis (ATN) is the most common cause of AKI in hospitalized patients, often due to ischemia or nephrotoxins.

Diagnosis & Evaluation - Kidney Detective Kit

• Clues: History (drugs, ↓intake), exam (volume, bladder).
• Urinalysis (U/A):
  • Pre-renal: Bland, high SpGr.
  • ATN: Muddy brown casts.
  • AIN: WBC casts, eosinophils (📌 Wright/Hansel).
  • GN: RBC casts.
• Urine Indices:
  • FeNa: <1% (Pre-renal) vs >2% (ATN).
  • FeUrea: <35% (Pre-renal, on diuretics).
• Bloods: ↑SCr, BUN:Cr >20:1 (Pre-renal), K↑, acidosis.
• Imaging: US KUB (obstruction? kidney size?).

⭐ Muddy brown granular casts in urine sediment are highly suggestive of Acute Tubular Necrosis (ATN).

Complications - AKI's Ripple Effect

• Fluid Overload: Pulmonary edema, hypertension, heart failure.
• Electrolyte Imbalances:
  • Hyperkalemia (≥5.5 mEq/L): Peaked T waves, arrhythmias. ⚠️ Most critical!
  • Hyponatremia, Hyperphosphatemia, Hypocalcemia.
  • Metabolic Acidosis (High Anion Gap).
• Uremic Syndrome:
  • Encephalopathy (asterixis).
  • Pericarditis (friction rub, tamponade risk).
  • Platelet dysfunction (bleeding tendency).
• Increased Infection Risk.
• Cardiovascular: MI, arrhythmias.
• Progression to CKD.

⭐ Uremic pericarditis is an absolute indication for dialysis in AKI.

Management Principles - Kidney Rescue Plan

• Stop nephrotoxic drugs (e.g., NSAIDs, contrast).
• Optimize volume status & maintain MAP >65 mmHg.
• Rule out/Relieve obstruction (e.g., bladder scan, catheter).
• Treat hyperkalemia, severe acidosis.
• Adjust drug dosages to renal function.
• Diuretics (furosemide) for volume overload; not for anuria/oliguria without overload.

⭐ RRT Indications (AEIOU): Acidosis (severe); Electrolytes (refractory hyperK+ >6.5); Intoxications; Overload (refractory); Uremia (symptomatic: pericarditis, encephalopathy).

High‑Yield Points - ⚡ Biggest Takeaways

• AKI (KDIGO): ↑SCr ≥0.3 mg/dL (48h) or ≥1.5x baseline (7d); UO <0.5 mL/kg/h (6h).
• Prerenal: Most common; BUN:Cr >20, FENa <1%; due to hypoperfusion.
• ATN: Intrinsic AKI; muddy brown casts, FENa >2%.
• Postrenal: Obstruction; anuria/polyuria; ultrasound is key.
• Dialysis (AEIOU): Refractory Acidosis, Electrolytes (K⁺>6.5), Intoxications, Overload, Uremia.
• CIN Prevention: IV hydration (isotonic saline) pre-contrast.
• Rhabdomyolysis AKI: ↑CK, myoglobinuria; treat with aggressive hydration, urine alkalinization.