Acute Kidney Injury (AKI)

Overview

• Definition: Deterioration in kidney function, also known as acute renal failure.
• Measurement: Glomerular Filtration Rate (GFR) is used to gauge kidney function.
• Functional Unit: Nephron, comprising the glomerulus and Bowman's capsule.

GFR and Creatinine Clearance

• GFR: Volume of filtrate through the glomerulus into the Bowman's capsule per unit time.
• Filtration Path: Filtrate passes through the nephron - proximal tubule, Loop of Henle, distal tubule, collecting duct, forming urine.
• Creatinine Clearance: Used to estimate GFR; creatinine is freely filtered by the glomerulus, not reabsorbed.
• Formulas:
  • Cockcroft-Gault formula for creatinine clearance.
  • Modification of Diet in Renal Disease (MDRD) formula.

Causes of AKI

• Pre-Renal Causes:

  • Reduction in blood perfusion to kidneys (e.g., hypovolemia from GI losses).
  • Conditions like hypotension, sepsis, pulmonary embolism.
  • Renal artery stenosis or aortic dissection.

• Intrinsic Causes:

  • Affect nephron directly, e.g., acute tubular necrosis (death of epithelial cells).
  • Can be due to Rhabdomyolysis, hemolysis, medications like aminoglycosides, Vancomycin.
  • Acute interstitial nephritis from drugs (e.g., penicillins, NSAIDs).
  • Glomerular diseases (Goodpasture's disease).

• Post-Renal Causes:

  • Obstruction beyond kidney (e.g., benign prostatic hypertrophy, tumors).
  • Less common: renal stones affecting one kidney.

Signs and Symptoms

• General Symptoms: Lethargy, nausea, delirium.
• Fluid Status: Can present as hypovolemic or fluid overload.
• Definition Criteria:
  • Increase in serum creatinine by 26 micromol/L in 48 hours.
  • 1.5x increase in baseline creatinine in 7 days.
  • Low urine production (< 0.5 ml/kg/hour for >6 hours).

Diagnosis

• Blood Tests: Raised serum creatinine, electrolytes imbalance.
• Urine Studies: Proteinuria, hematuria, urine microscopy for casts.
• Imaging: Ultrasound, CT scan.
• Biopsy: Sometimes needed for intrinsic causes.

Treatment

• General Management:

  • Intravenous fluids to promote renal perfusion (except in fluid overload).
  • Review & adjust medications (DAM mnemonic: Diuretics, ACE inhibitors, Metformin).
  • Correct electrolyte imbalances (e.g., treat hyperkalemia).

• Specific Interventions:

  • Relieve obstructions with catheter if necessary.
  • Monitor urine output, fluid intake, daily weights.
  • Renal replacement therapy (e.g., hemodialysis) in severe cases.

Notes

• AKI is common in hospital settings, often first identified by blood tests.
• Electrolyte imbalances due to reduced kidney function should be treated promptly.
• Imaging and biopsies are crucial for diagnosing structural or intrinsic causes.
• Treatment depends on the severity and underlying cause of AKI.