Acute kidney injury

Definition of acute kidney injury (AKI)

  • Abrupt (< 48 hrs) increase in Cr ≥ 0.3 mg/dL from baseline Cr
  • Cr ≥ 1.5 x baseline in past 7 days
  • or oliguria (< 0.5 ml/kg/hr) for > 6 hrs

Notes

  • Cr is only a surrogate of GFR in steady state - cannot rely on calculated eGFR in AKI!
  • More chronic kidney injury a/w anemia, small echogenic kidneys, ↓Ca, ↑PO4
  Prerenal Intrinsic Postrenal
Pathophys
  • ↓ renal perfusion, with maximized renal compensation to retain Na
  • No damage to kidney structures
  • Kidney parenchyma is damaged leading to ↓ GFR
  • Obstruction from renal pelvis to urethra (typically b/l or solitary kidney to cause AKI)
  • Increased pressure damages nephrons, causes hydronephrosis
Etiology
  • Hypovolemia
  • Poor forward pressure - hypotension, CHF, MI
  • Hemodynamic - afferent vasoconstriction (NSAIDs, cyclosporine/tacrolimus, amphotericin B), efferent vasodilation (ACEi, ARB), IV dye 
  • Hypercalcemia
  • Hepatorenal syndrome
  • Glomerular
  • Vascular -
  • Interstitial - "allergic reaction" in the kidney. Meds (penicillins, cephalosporins, sulfonamides, phenytoin, PPIs, NSAIDS), systemic disease (sarcoid, Sjogren's)
  • Tubular (ATN) - ischemic (prolonged prerenal, sepsis, hypotension), nephrotoxic (aminoglycosides, methotrexate, amphotericin, cisplatin, myoglobin, IV contrast)
  • Prostate (BPH, cancer), neurogenic bladder, intraureteral (stone/clot/tumors), extraureteral (compression from tumor, retroperitoneal fibrosis) 
Labs BUN/Cr > 20 Normal (10-15) Variable
FeNa < 1% > 2% Variable
UOsm > 500 mOsm/kg ~ 300 mOsm/kg Variable
UA Bland Muddy brown casts Bland
Management
  • Look at volume status: prerenal does not = dry/give IVF; may need inotropes or diuresis to improve cardiac output/renal perfusion
  •  ATN - treat low perfusion state, identify risk factors, withdraw offending agents
  • maintain fluid, electrolyte, acid-base balance
  • renal replacement therapy as needed (AEIOU), but mostly just wait for kidney to recover...(7-21 d), usually return to baseline
  • Straight cath/Foley
  • Renal u/s to rule out hydronephrosis
  • Post-obstructive diuresis over next 24 hrs
    • Make sure to maintain fluid balance/PO intake; q12 electrolytes
  • Cr should downtrend soon (e.g. next morning)

Glomerular perfusion pressure

author: last edited: Oct. 24, 2018, 8:58 a.m. | pk: 112 | unpublished