What are the differences in management and treatment of prerenal (Acute Kidney Injury (AKI) due to decreased blood flow) vs intrarenal (AKI due to kidney damage) vs postrenal (AKI due to obstruction) Acute Kidney Injury (AKI)?

Management of Prerenal vs Intrarenal vs Postrenal Acute Kidney Injury

The management of AKI must be tailored to its specific etiology (prerenal, intrarenal, or postrenal), with prompt identification and treatment of the underlying cause being the cornerstone of effective therapy for all types. 1

Diagnostic Approach to AKI Classification

Initial Assessment

• Laboratory evaluation: Serum creatinine, BUN, complete blood count, urinalysis with microscopy, urine electrolytes, and fractional excretion of sodium (FENa) 1
• FENa interpretation:
  • <1%: Suggests prerenal AKI or hepatorenal syndrome

  • 2%: Suggests intrinsic renal disease (ATN) 1

• Renal ultrasonography: Essential to rule out obstruction, particularly in older men 1, 2

Key Differentiating Features

• Prerenal AKI (68% of cases): Due to decreased renal perfusion 1
• Intrarenal AKI: Primarily acute tubular necrosis (ATN), due to direct kidney damage 1
• Postrenal AKI: Due to urinary tract obstruction 1

Management of Prerenal AKI

Causes

• Volume depletion (hemorrhage, vomiting, diarrhea)
• Excessive diuresis
• Decreased effective circulating volume (heart failure, cirrhosis)
• Excessive diuretic use 1

Management Approach

1. Volume Restoration:

   • Isotonic crystalloids for volume depletion 1
   • Packed red blood cells for hemorrhage (maintain Hgb 7-9 g/dL) 1

2. Medication Adjustments:

   • Discontinue diuretics, NSAIDs, ACE inhibitors, ARBs 1
   • In cirrhosis: Also discontinue beta-blockers 3, 1

3. Special Considerations for Cirrhosis:

   • For tense ascites: Therapeutic paracentesis with albumin infusion 3, 1
   • For hepatorenal syndrome: Albumin infusion (1 g/kg up to 100g) for 2 days 1
   • If no response: Add vasoactive agents (terlipressin 1 mg every 4-6 hours) 1

4. Monitoring:

   • Daily serum creatinine and electrolytes
   • Strict fluid balance monitoring
   • Daily weight measurements 1

5. Recovery Timeline:

   • Prerenal AKI typically recovers within 7 days with proper treatment 4

Management of Intrarenal AKI

Causes

• Ischemia
• Nephrotoxins (medications, contrast media)
• Inflammation (glomerulonephritis, interstitial nephritis) 1

Management Approach

1. Remove Offending Agents:

   • Discontinue all nephrotoxic medications 1
   • Adjust medication dosages for reduced kidney function 1

2. Supportive Care:

   • Restore and maintain adequate renal perfusion
   • Target euvolemia with careful fluid management
   • Avoid both hypovolemia and fluid overload 1

3. Specific Treatments Based on Cause:

   • Acute interstitial nephritis: Consider corticosteroids (prednisone 1 mg/kg/day) for persistent or severe cases 1
   • Glomerulonephritis: Specific immunosuppressive regimens based on type 1
   • Immune checkpoint inhibitor nephritis: Interrupt or discontinue immunotherapy; methylprednisolone 1 mg/kg for moderate cases 1

4. Recovery Timeline:

   • BUN and creatinine levels typically remain elevated beyond 7 days 4
   • Requires longer follow-up than prerenal AKI 4

Management of Postrenal AKI

Causes

• Prostatic hypertrophy
• Nephrolithiasis
• Malignancy
• Retroperitoneal fibrosis 1

Management Approach

1. Relieve Obstruction:

   • Urinary catheterization for lower tract obstruction
   • Nephrostomy tube or ureteral stent for upper tract obstruction 2

2. Definitive Treatment:

   • Address underlying cause (e.g., prostate surgery, stone removal) 2

3. Monitor for Post-obstructive Diuresis:

   • Replace fluid and electrolyte losses
   • Avoid volume depletion during diuretic phase 2

4. Recovery Timeline:

   • BUN levels typically normalize around day 7 after obstruction relief 4

Indications for Renal Replacement Therapy (All Types)

Consider dialysis for:

• Refractory hyperkalemia
• Volume overload unresponsive to diuretics
• Intractable acidosis
• Uremic encephalopathy, pericarditis, or pleuritis
• Removal of certain toxins 2

Follow-up After AKI (All Types)

• Follow-up within 1 month of AKI diagnosis
• Serial measurements of serum creatinine and proteinuria
• Monitor for development of chronic kidney disease
• Cardiovascular risk assessment 1
• Risk stratification based on AKI severity for timing of follow-up 3

Common Pitfalls to Avoid

1. Delayed Recognition of Obstruction:

   • Always consider renal ultrasonography, especially in older men 2

2. Continued Nephrotoxin Exposure:

   • Avoid nephrotoxic medications when possible
   • Careful monitoring when nephrotoxins are necessary 1

3. Inadequate Volume Assessment:

   • Both hypovolemia and fluid overload can worsen AKI 1

4. Missing AKI in Cirrhosis:

   • Use adapted KDIGO criteria for diagnosis (increase in SCr of >0.3 mg/dl from baseline within 48h, or ≥50% increase from baseline within three months) 3

5. Inadequate Follow-up:

   • Even one episode of AKI increases risk of cardiovascular disease, chronic kidney disease, and death 5
   • Long-term follow-up is essential, particularly for more severe AKI 3