Pocket-Card_Acute-Kidney-Injury_March-2024

Acute Kidney Injury (AKI)

Definition of Acute Kidney Injury

  • Formerly known as acute renal failure, acute kidney injury (AKI) is characterized as a reversible and rapid reduction in glomerular filtration rate (GFR) or kidney function.
  • Results in an increase in serum blood urea nitrogen (BUN), creatinine, and metabolic waste products.
  • If untreated, AKI can lead to:
    • Reduced urine output
    • Fluid retention
    • Volume overload
    • Irreversible loss of kidney cells and nephrons, subsequently leading to chronic kidney disease.

Clinical Definition (KDIGO, 2012)

  • The Kidney Disease: Improving Global Outcomes (KDIGO) defines AKI by any of the following criteria:
    • Increase in serum creatinine (SCr) by ≥ 0.3 mg/dL (25.6 µmol/L) within 48 hours
    • Increase in SCr by ≥ 1.5 times baseline, presumed to have occurred within the previous 7 days
    • Urine volume < 0.5 mL/kg/hour for 6 hours

Classifications of Acute Kidney Injury

Prerenal AKI
  • Pathophysiology: Decreased blood flow to the kidneys (decreased renal perfusion).
  • Causes:
    • Absolute decrease in circulating volume (Banasik, 2022):
    • Vomiting, diarrhea
    • Hemorrhage
    • Burns
    • Dehydration
    • Relative decrease in circulating volume:
    • Systemic vasodilation and hypotension caused by:
      • Sepsis
      • Anaphylaxis
      • Anesthesia
      • Drug overdose
Intrarenal (Intrinsic) AKI
  • Pathophysiology: Structural injury within the kidney causing vessel constriction.
  • Causes:
    • Tubular:
    • Ischemic: Acute tubular necrosis, prolonged prerenal failure, transfusion reaction, rhabdomyolysis.
    • Nephrotoxic: Medications (NSAIDs, certain antibiotics, cytotoxic chemotherapeutics, heroin, amphetamines), heavy metals, snake and insect venom.
    • Glomerular: Acute glomerulonephritis
    • Interstitial:
    • Allergic interstitial nephritis
    • Acute pyelonephritis
    • Vascular:
    • Vasculitis
    • Emboli
    • Nephrosclerosis (from chronic hypertension, hypertensive urgencies and emergencies)
    • Coagulation defects
    • Leukemia, lymphoma
Postrenal AKI
  • Pathophysiology: Blockage along the urinary tract obstructing urine outflow from the kidney.
  • Causes:
    • Renal calculi
    • Emboli
    • Prostate enlargement
    • Genetic anatomic narrowing
    • Intra-abdominal tumors
    • Urinary tract strictures
    • Kinked or obstructed indwelling urinary catheters

Contrast-Induced Acute Kidney Injury (CI-AKI)

(KDIGO, 2012; Rudnick & Davenport, 2024)

  • CI-AKI may occur in patients receiving iodinated radiocontrast for imaging procedures.
  • Risk factors include:
    • Impaired renal function
    • Advanced age
    • Diabetes
    • Hypertension
    • Congestive heart failure
    • Chronic kidney disease
    • Volume depletion
    • Hemodynamic instability
    • Concurrent nephrotoxic medications
    • Use of high volume and/or high osmolality contrast agents
  • For patients at high risk, prevention measures include:
    • Confirming the necessity of contrast material.
    • Considering alternative imaging methods that do not use contrast.