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Acute Kidney Injury for NP

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Acute Kidney Injury (AKI) for the Nurse Practitioner Licensing Exam
Definition
  • Acute Kidney Injury (AKI): A sudden decrease in kidney function that occurs over hours to days, characterized by an inability to regulate fluid, electrolytes, and waste. AKI is identified by a rise in serum creatinine or a reduction in urine output.
  • Diagnosis Criteria:
    • Increase in serum creatinine by ≥0.3 mg/dL in 48 hours or ≥1.5 times baseline within 7 days.
    • Urine output <0.5 mL/kg/h for at least 6 hours.
Etiology
  • Prerenal AKI:
    • Caused by reduced renal perfusion without structural kidney damage.
    • Causes: hypovolemia (e.g., dehydration), heart failure, sepsis, or renal artery stenosis.
  • Intrinsic AKI:
    • Direct kidney damage, commonly involving the tubules.
    • Causes: Acute Tubular Necrosis (ATN) from ischemia or nephrotoxins (e.g., contrast dye, medications), Acute Interstitial Nephritis (AIN) from drug reactions, and glomerulonephritis.
  • Postrenal AKI:
    • Obstruction of urinary outflow, such as from kidney stones, benign prostatic hyperplasia (BPH), or ureteral obstruction.
Acute Kidney Injury Etiologies
Clinical Presentation
  • Symptoms:
    • Oliguria (urine output <400 mL/day), fatigue, nausea, edema, and signs of fluid overload (e.g., dyspnea, peripheral edema).
  • Physical Exam:
    • Signs of dehydration (dry mucous membranes, low blood pressure) in prerenal AKI.
    • Flank pain or bladder distention in postrenal AKI.
Diagnosis
  • Lab Tests:
    • Serum Creatinine: Elevated.
    • Urine Studies:
    • Prerenal: Low urine sodium (<20 mEq/L), high specific gravity.
    • ATN: Muddy brown casts, urine sodium >40 mEq/L.
  • Imaging:
    • Renal ultrasound to rule out postrenal causes like obstruction.
Management
  • Prerenal AKI: Volume resuscitation with fluids or blood products.
  • Intrinsic AKI: Supportive care, managing electrolytes, and discontinuing nephrotoxins.
  • Postrenal AKI: Relieve obstruction (e.g., catheterization, stone removal).
Complications
  • Hyperkalemia: Can lead to arrhythmias.
  • Metabolic Acidosis: Due to impaired acid excretion.
  • Uremia: Can cause encephalopathy or pericarditis.
Key Points
  • AKI is diagnosed by a rise in serum creatinine or decreased urine output.
  • Causes are prerenal (hypoperfusion), intrinsic (ATN, AIN), and postrenal (obstruction).
  • Diagnosis is made using serum creatinine, urine analysis, and renal ultrasound.
  • Treatment focuses on addressing the underlying cause, managing complications like hyperkalemia, and preventing progression.

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