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
Acute glomerulonephritis. Most common type in children is following a streptococcal infection but rare in adults, with poorer prognosis in adults.

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
Creatinine: rising=acute, progressing, stable=chronic, decrease=improving

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 BUN:Cr 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
Creatinine: rising=acute, progressing, stable=chronic, decrease=improving

17. Diagnostic tests Renal function – GFR Fractional excretion of sodium
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
Creatinine: rising=acute, progressing, stable=chronic, decrease=improving

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
<1% in glomerulonephritis, vasculitis, acute urinary obstruction too

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

20. RBC cast Damaged glomerular basement membrane
Although the red blood cells may enter the urinary stream via disrupted tubular elements, their most common means of entry is through a damaged glomerular basement membrane. The presence of these casts indicates a glomerular injury. In some cases the erythrocytes are destroyed. The typical sign for these erythrocytes casts is a red brown mass. Other renal diseases that may or may not cause direct damage to or destroy the glomerulus and which give rise to blood cell casts and hematuria. The more common of these include acute pyelonephritis and renal infarction

21. RBC cast

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

23. WBC cast
They consist of mucoprotein casts with incorporated leukocytes. With chronical renal inflammation, especially with pyelonephritis, the leukocytes enter the urinary stream through two major pathways, transglomerular or transtubular

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 Renal ultrasound
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
Diuretics might have harmful effect – not to use to increase urine output

32. References
Acute tubular necrosis.
Acute renal failure