Acute Renal Failure

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Acute Renal Failure

• Malcolm Cox, M.D.

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Acute Renal FailureDefinition

• Acute decrement in GFR
• May heal partially or completely or progress to
  more severe renal insufficiency, including
  end-stage renal disease

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Review
9.0
8.0
Serum Creatinine (mg/dl)
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
40
60
80
100
120
140
160
180
20
0
Inulin Clearance (ml/min per 1.73m2)
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Acute Renal FailureClassification

• Pre-renal (functional)
• Renal (structural)
• Post-renal (obstruction)

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Acute Renal FailurePre-renal Causes

• Intravascular volume depletion
• Hemorrhage
• Sodium depletion
• Redistribution of ECF
• Third space accumulation
• Edematous disorders
• Drugs

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Renal Blood Flow
Review
F ?P/R
7
Review
Raff
Reff
PGC
RAP
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Pre-Renal AzotemiaPathophysiology

• Renal hypoperfusion
• Decreased RBF and GFR
• Increased filtration fraction (GFR/RBF)
• Increased Na and H2O reabsorption
• Oliguria, high Uosm, low UNa
• Elevated BUN/Cr ratio

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Acute Tubular NecrosisClassification

• Ischemic
• Nephrotoxic

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Acute Tubular Necrosis
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Acute Tubular Necrosis
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Acute Renal FailureNephrotoxic ATN

• Endogenous Toxins
• Heme pigments (myoglobin, hemoglobin)
• Myeloma light chains
• Exogenous Toxins
• Antibiotics (e.g., aminoglycosides, amphotericin
  B)
• Radiocontrast agents
• Heavy metals (e.g., cis-platinum, mercury)
• Poisons (e.g., ethylene glycol)

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Acute Tubular Necrosis
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Acute Tubular Necrosis
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Acute Interstitial NephritisCauses

• Allergic interstitial nephritis
• Drugs
• Infections
• Bacterial
• Viral
• Sarcoidosis

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Allergic Interstitial NephritisClinical
Characteristics

• Fever
• Rash
• Arthralgias
• Eosinophilia
• Urinalysis
• Microscopic hematuria
• Sterile pyuria
• Eosinophiluria

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Acute Interstitial Nephritis
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Cholesterol Embolization
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Contrast-Induced ARFPrevalence

• Less than 1 in patients with normal renal
  function
• Increases significantly with renal insufficiency

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Contrast-Induced ARFRisk Factors

• Renal insufficiency
• Diabetes mellitus
• Multiple myeloma
• High osmolar (ionic) contrast media
• Contrast medium volume

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Contrast-induced ARFClinical Characteristics

• Onset - 24 to 48 hrs after exposure
• Duration - 5 to 7 days
• Non-oliguric (majority)
• Dialysis - rarely needed
• Urinary sediment - variable
• Low fractional excretion of Na

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Contrast-induced ARFProphylactic Strategies

• Use I.V. contrast only when necessary
• Hydration
• Minimize contrast volume
• Low-osmolar (nonionic) contrast media
• N-acetylcysteine, fenoldopam

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Acute Renal FailurePost-renal Causes

• Intra-renal Obstruction
• Acute uric acid nephropathy
• Drugs (e.g., acyclovir)
• Extra-renal Obstruction
• Renal pelvis or ureter (e.g., stones, clots,
  tumors, papillary necrosis, retroperitoneal
  fibrosis)
• Bladder (e.g., BPH, neuropathic bladder)
• Urethra (e.g., stricture)

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Acute Renal FailureDiagnostic Tools

• Urinary sediment
• Urinary indices
• Urine volume
• Urine electrolytes
• Radiologic studies

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Urinary Sediment (1)

• Bland
• Pre-renal azotemia
• Urinary outlet obstruction

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Urinary Sediment (2)

• RBC casts or dysmorphic RBCs
• Acute glomerulonephritis
• Small vessel vasculitis

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Red Blood Cell Cast
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Red Blood Cells
Monomorphic
Dysmorphic
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Dysmorphic Red Blood Cells
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Dysmorphic Red Blood Cells
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Urinary Sediment (3)

• WBC Cells and WBC Casts
• Acute interstitial nephritis
• Acute pyelonephritis

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White Blood Cells
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White Blood Cell Cast
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Urinary Sediment (4)

• RTE cells, RTE cell casts, pigmented granular
  (muddy brown) casts
• Acute tubular necrosis

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Renal Tubular Epithelial Cell Cast
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Pigmented Granular Casts
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Acute Renal FailureUrine Volume (1)

• Anuria (lt 100 ml/24h)
• Acute bilateral arterial or venous occlusion
• Bilateral cortical necrosis
• Acute necrotizing glomerulonephritis
• Obstruction (complete)
• ATN (very rare)

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Acute Renal FailureUrine Volume (2)

• Oliguria (100-500 ml/24h)
• Pre-renal azotemia
• ATN
• Non-Oliguria (gt 500 ml/24h)
• ATN
• Obstruction (partial)

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Acute Tubular NecrosisClinical Characteristics
Characteristic Oliguric ATN Non-Oliguric ATN
Incidence 41 59
Toxin-induced 8 30
UV (ml/24h) lt 400 1,280 75
UNa (mEq/L) 68 6 50 5
FENa () 6.8 1.4 3.1 0.5
Dialysis required 84 26
Mortality 50 25
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Acute Renal FailureUrinary Indices
ATN
ATN
ATN
PR
PR
500
40
40
1.0
1.0
350
20
20
PR
ATN
ATN
PR
PR
(U/P)Cr
UNa (mEq/L)
UOsm (mOsm/L)
FENa
RFI
41
Hydronephrosis
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Normal Renal Ultrasound
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Hydronephrosis
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Hydronephrosis