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Acute Renal Failure

Acute Renal Failure

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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