prerenal azotemia

Introduction

Decreased perfusion of the kidneys.

Also see acute renal failure.

Etiology

• volume depletion (most common)
  • decreased fluid intake
  • increased fluid losses
    • diarrhea
    • nasogastric suction
    • vomiting
    • hemorrhage
    • burns
    • surgical drainage
    • adrenal insufficiency
  • decreased intravascular volume
    • accumulation of fluid in extravascular compartments (3rd spacing)
      • pancreatitis
      • peritonitis
    • severe hypoalbuminemia
      • cirrhosis with ascites
• hypotension (mean blood pressure* < 60 mm Hg)
  • decreased systemic vascular resistance
    • sepsis
    • drug overdoses
    • excessive antihypertensive treatment
    • anaphylaxis
    • peripheral vasodilation
  • low cardiac output
    • myocardial, pericardial & valvular heart disease
    • cardiac arrhythmias
    • pericardial tamponade
    • increased pulmonary vascular resistance
      • pulmonary hypertension
      • pulmonary embolus
      • positive pressure mechanical ventilation
  • NSAIDs* alter glomerular hemodynamics & raise the blood pressure threshold for prerenal azotemia
• renal vasoconstriction
  • cyclosporine A
  • vasopressors (norepinephrine, epinephrine, phenylephrine)
  • amphotericin B
  • hypercalcemia (increased ionized Ca+2)
• renal hypoperfusion
  • cyclooxygenase inhibitors
  • ACE inhibitors
• renal vascular disease
  • renal artery stenosis
  • renal arterial thrombosis
  • renal embolic disease
• hyperviscosity syndrome (rare)
  • multiple myeloma
  • macroglobulinemia
  • polycythemia

Epidemiology

• more common in elderly

Pathology

• stimulation of sympathetic nervous system
• stimulation of renin-angiotensin-aldosterone axis
• increased renal tubular Na+ reaborption (proximal tubules & distal tubules)
• increased plasma ADH -> increased water resorption in the distal renal tubules

Clinical manifestations

• orthostasis
• hypotension
• signs of dehydration
• signs of 3rd-spacing may be present
• oliguria
• signs of extracellular fluid volume depletion are absent in 50% of patients

Laboratory

• urine osmolality > 500 mosm/kg
• urine Na+ < 20 meq/L
• fractional excretion of Na+ (FENA) <1%
  • diuretic use may result in a high FENA
• increased urine creatinine
• microscopic evaluation of the urine is unremarkable

Management

• optimize volume status
  • normal saline for volume depletion
  • treat underlying congestive heart failure
  • normalize extracellular fluid volume
    • diuretics if indicated
• discontinue offending pharmacologic agents
• treat hypercalcemia
  • loop diuretics
  • volume repletion
  • AVOID thiazide diuretics (enhanced renal tubular Ca+2 resorption)

More general terms

• azotemia

Additional terms

• acute renal failure (ARF)
• glomerular filtration rate (GFR)
• hypercalcemia
• renal artery stenosis (RAS)