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Acute Renal Failure

Acute Renal Failure. Hai Ho, M.D. What is acute renal failure?. Impairment of kidney function leading to retention of substances normally excreted by the kidney Hours and days. Epidemiology. Overall mortality rate: 40-50%. Kidney anatomy & physiology. Kidney anatomy & physiology.

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Acute Renal Failure

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  1. Acute Renal Failure Hai Ho, M.D.

  2. What is acute renal failure? • Impairment of kidney function leading to retention of substances normally excreted by the kidney • Hours and days

  3. Epidemiology • Overall mortality rate: 40-50%

  4. Kidney anatomy & physiology

  5. Kidney anatomy & physiology

  6. Compartmentalize causes? • Prenal • Renal or intrinsic • Postrenal

  7. Pathophysiology of prerenal failure? Hypoperfusion to the kidney

  8. Common causes of prerenal failure? • Hypovolumia • Bleeding • Burn • Dehydration from GI loss • Hypervolumia • Congestive heart failure • Third-spacing – cirrhosis, acute pancreatitis • Peripheral vasodilation • Septic shock

  9. Common cause of intrinsic renal failure? • Acute tubular necrosis – most common cause of acute renal failure in hospitalized patients • Glomerulonephritis – rare, common in children after streptococcal infection

  10. What is acute tubular necrosis? Disorder resulting from damage of renal tubule cells

  11. What cause acute tubular necrosis? • Prerenal azotemia • Ischemia > 30 minutes • Most common in hospitalized patients • Rhabdomyolysis • Contrast dye • Drugs • Aminoglycosides • Amphotericin • NSAID • ACE-inhibitor

  12. Common cause of postrenal failure? • Ureteric obstruction – tumors, stones • Bladder outflow obstruction (prostatism)

  13. Clinical presentations of acute renal failure? • Asymptomatic • Decreased or no urine output • Hypervolumia • Pulmonary edema – tachycardia, tachapnea • Peripheral edema • Uremia – lethargy, nausea, anorexia • Arrhythmia – hyperkalemia, acidosis

  14. Diagnostic tests • Renal function – GFR • Plasma creatinine • May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR • Interesting in the trend rather than absolute value • Affect by muscle mass • Creatinine clearance • Stable renal function • Cockcroft-Gault equation

  15. Cockcroft-Gault equation (140-age) x lean body weight (kg) --------------------------------------------- PCr (mg/dL) x 72 Women – multiple by 0.85

  16. Diagnostic tests • Renal function – GFR • Plasma creatinine • May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR • Interesting in the trend rather than absolute value • Creatinine clearance • Stable renal function • Cockcroft-Gault equation • BUN:Cr • 15:1 to 20:1 – prerenal, due to increased BUN absorption • 10:1 – cirrhosis or other hypoprotein state

  17. Diagnostic tests • Renal function – GFR • Plasma creatinine • May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR • Interesting in the trend rather than absolute value • Creatinine clearance • Stable renal function • Cockcroft-Gault equation • Fractional excretion of sodium

  18. Fractional excretion of sodium UNa x PCr • FENa = --------------- x 100 PNa x UCr • Interpretation • <1% – prerenal, glomerulonephritis, obstruction • >2% – ATN • 1-2% - either prerenal or ATN • Not accurate before diuretics or IVF

  19. Diagnostic tests • Urinalysis • Dipstick – hematuria and proteinuria • Microscopic examination • RBC cast – glomerulonephritis

  20. RBC cast Damaged glomerular basement membrane

  21. RBC cast

  22. Diagnostic tests • Urinalysis • Dipstick – hematuria and proteinuria • Microscopic examination • RBC cast – glomerulonephritis • WBC cast – acute pyelonephritis

  23. WBC cast

  24. Diagnostic tests • Urinalysis • Dipstick – hematuria and proteinuria • Microscopic examination • RBC cast – glomerulonephritis • WBC cast – infection such as pyelonephritis • Granular cast – protein aggregate or degenerative cellular casts as in acute tubular necrosis

  25. Granular cast

  26. Granular cast

  27. Diagnostic tests • Urinalysis • Dipstick – hematuria and proteinuria • Microscopic examination • RBC cast – glomerulonephritis • WBC cast – infection such as pyelonephritis • Granular cast – protein aggregate or degenerative cellular casts as in acute tubular necrosis • Positive blood on dipstick but negative RBC on microscopic exam - rhadomyolysis • Renal ultrasound

  28. Renal ultrasound? • Obstruction – hydronephrosis • Chronic disease – atrophic kidney

  29. Renal biopsy Selective cases such as glomerulonephritis, vasculitis, nephrotic syndrome

  30. Treatment? • Treat the underlying cause • Prerenal – increase perfusion • Intrinsic – if possible, remove the culprit • Postrenal – relieve the obstruction

  31. General management • Hyperkalemia – low K diet, lasix, insulin/glucose, NaHCO3, Kayexalate, Ca gluconate • Fluid retention and overload – diuresis, fluid restriction • Diet – low protein, high carbohydrates • Acetylcysteine with 0.45% NS with contrast study – reduce nephropathy • Dialysis

  32. References • Acute tubular necrosis. http://www.nlm.nih.gov/medlineplus/ency/article/000512.htm • Acute renal failure http://www.firstconsult.com/ • http://www.supermt.com.tw/URNfiles/image/CASTS/RBCCAST/RBC%20cast.htm

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