Acute Renal Failure : Assessment and Management

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Acute Renal Failure Assessment and Management

• Pat Melanson, MD

• Royal Victoria Hospital

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Acute Renal Failure Definition

• An abrupt decrease in the clearance of
  nitrogenous wastes by the kidneys
• manifested by increases in BUN, Cr and a
  decrease in urine output

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Acute Renal Failure Background

• 10 - 30 of ICU patients

• 40 - 80 mortality if require HD

• six times increase in mortality

• all aspects of the therapy of ATN, including
  dialysis, are basically supportive

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ARF Pre-renal Causes

• volume depletion
• volume redistribution
• reduced cardiac output
• hypoperfusion
• 50 of hospitalized patients

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ARF Intrinsic Causes

• ATN - ischemia, hypoxia, toxins

• AGN

• AIN

• Acute renovascular disease

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ARF Post-renal Causes

• obstruction

• papillary necrosis

• retroperitoneal fibrosis

• bladder outlet

• 1 - 15 of hospitalized patients

• easily reversible

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ARF Diagnosis

• History and Physical

• Urinalysis

• Urinary indices

• Hemodynamics and fluid challenge

• Renal biopsy

• Radiology - Ultrasound, IVP, AXR

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Urinary Indices
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Urine Sodium

• decreased renal perfusion

• increased sodium reabsorption

• decreased urine sodium excretion

• intrinsic renal impairment

• impaired Na reabsorption

• diuretic therapy

• obligatory losses in elderly

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Fractional Excretion of Na

• the fraction of Na filtered at the glomerulus
  that is excreted in the urine

• FEna Una x Pcr

• Pna x Ucr

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Urinalysis

• abundant tubular epithelial cells

• epithelial cell casts

• WBC casts

• eosinophils

• pigmented casts

• RBC casts

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Urinalysis

• abundant tubular epithelial cells
• epithelial cell casts
• WBC casts
• eosinophils
• pigmented casts
• RBC casts

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ARF Pathogenesis
Glomerulus
Efferent
Afferent
Decreased permeabilty
Vasoconstiction
Backleak
Obstruction
Proximal tubule
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• ARF Pathophysiology
• Increased cytosolic Calcium
• Phospholipases
• Nitric oxide
• free radicals

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Treatment of ARF Diuretics

• loop diurtics may vasodilate

• decrease renal O2 demand

• high flow may decrease obstruction

• increase urine output

• no benefits re duration, HD, mortality

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Treatment of ARF CCB

• renal hemodynamics
• inhibiting cellular calcium uptake
• protective in transplants

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Treatment of ARF Dopamine

• improves urine output synergistically with
  furosemide

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Renal Dose Dopamine

• 1960s

• Dopamine led to natruresis in CHF

• increased GFR,Naexcretion in volunteers

• also increased C.I. 1.4 L/min

• renal function only improved when C.I. Increased

• concluded selective renal vasodilation occurred
  because MAP stayed constant

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Renal Dose Dopamine

• Animal Evidence

• no studies show increased RBF without increased
  C.O.

• no evidence for selective renal vasodilation

• diuretic ( Na/K ATPase inhibitor)

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Renal Dose Dopamine

• Human Studies

• none show increase in CrCl,GFR unless increase
  in C.O.

• None show decrease ARF or need for HD

• Increased natruresis( vs Dobutamine)

• Blocks NE-induced renal vasoconstriction in
  healthy volunteers

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Renal Dose Dopamine Detrimental Effects

• Unknown endocrine and immune effects

• Adverse effects on splanchnic circulation

• Increased myocardial oxygen demand

• Arrythmogenic

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Renal Dose Dopamine

• increases renal blood flow

• increases urine output

• No improvement in renal function

• No decrease in need for HD

• No improvement in outcome

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Approach to ARF

• Rule out post-renal causes

• Maximize CVP, PCWP

• Maximize Cardiac Output

• Remove potential toxins

• Adjust doses of renal excreted drugs

• maintenance of nutritional, volume, and
  electrolyte homeostasis

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Treatment of ARF supportive

• maintenance of euvolemia

• blood pressure control

• electrolytes, acid-base

• nutritional therapy

• 0.6 gm/kg/d of protein

• infection

• GI bleeds

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ARF Management

• Fluid balance - ins/outs, weights

• Electrolytes and acid-base

• K

• avoid hyponatremia

• monitor, HCO3, Mg, PO4

• Treat only symptomatic hypocalcemia

• Nutrition - caloric intake, protein restriction

• Review all meds and adjust dosages

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ARF Indications for Dialysis

• fluid overload

• hyperkalemia

• acidosis

• uremia - pericarditis, encephalopathy, bleed

• BUN, Creatinine

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Dialysis Continuous vs Intermittant

• HD

• second hit hypotension

• CAVH-D, CVVH-D

• hemodynamic stability

• fluid balance flexibility

• nutritional flexibility

• metabolic control