Acute Kidney Injury (AKI) Lecture Notes

Definition of AKI

• Acute Kidney Injury (AKI): Previously known as acute renal failure.
  • Represents deterioration in kidney function.
  • Measured by glomerular filtration rate (GFR).

Key Concepts

• Glomerular Filtration Rate (GFR): Measures kidney's blood filtering ability.

  • Involves nephrons, specifically the glomerulus and Bowman's capsule.
  • Filtrate passes through various parts of the nephron, forms urine.

• Creatinine Clearance: Used to estimate GFR.

  • Creatinine: Breakdown product from muscle, filtered by kidneys.
  • Cockcroft-Gault formula: Estimates creatinine clearance using age, mass, gender, serum creatinine.
  • Alternative formula: Modification of diet in renal disease study group formula.

Causes of AKI

• Pre-renal Causes: Reduced blood perfusion to kidneys.

  • Causes: Hypovolemia (GI losses, hemorrhages, burns), hypotension, cardiogenic, distributive (sepsis, anaphylaxis), obstructive (pulmonary embolism).
  • Other factors: Renal artery stenosis, aortic dissection.

• Intrinsic Causes: Affect nephron components directly.

  • Factors: NSAIDs affect afferent arteriole, ACE inhibitors affect efferent arteriole.
  • Conditions: Acute tubular necrosis (due to pre-renal injury, rhabdomyolysis), acute interstitial nephritis, glomerular diseases, vascular conditions.

• Post-renal Causes: Obstructions beyond the kidney.

  • Examples: Benign prostatic hypertrophy, tumors, strictures, renal stones (less common).

Symptoms and Diagnosis

• Symptoms: Vary depending on cause; general lethargy, nausea, delirium.

  • Urine production patterns may indicate AKI.
  • Volume status may show hypovolemia or fluid overload.

• Diagnosis:

  • Serum Creatinine Increase: 26 micromoles per liter in 48 hours or 1.5x baseline in 7 days.
  • Urine Production: Less than 0.5 ml/kg/hr for >6 hours.

• Tests:

  • Blood tests (creatinine, electrolytes), urine studies (proteinuria, hematuria), imaging (ultrasound, CT scan), biopsy for intrinsic causes.

Treatment of AKI

• General Approach:

  • IV fluids to promote renal perfusion unless fluid overload exists.
  • Review medications using mnemonic DAM (Diuretics, ACE inhibitors, Metformin).
  • Correct electrolyte imbalances (e.g., calcium gluconate for hypokalemia).

• Specific Treatments:

  • Obstructions: Relieve via catheter.
  • Severe Cases: Renal replacement therapy (hemodialysis) for severe acidosis, hyperkalemia, drug intoxications, or refractory cases.

Conclusion

• AKI is common in hospitals with various underlying causes.
• Requires careful diagnosis and treatment to address underlying causes and manage symptoms.