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prerenal azotemia
Decreased perfusion of the kidneys.
Also see acute renal failure.
Etiology:
1) volume depletion (most common)
a) decreased fluid intake
b) increased fluid losses
1] diarrhea
2] nasogastric suction
3] vomiting
4] hemorrhage
5] burns
6] surgical drainage
7] adrenal insufficiency
c) decreased intravascular volume
1] accumulation of fluid in extravascular compartments (3rd spacing)
a] pancreatitis
b] peritonitis
2] severe hypoalbuminemia
-> cirrhosis with ascites
2) hypotension (mean blood pressure* < 60 mm Hg)
a) decreased systemic vascular resistance
1] sepsis
2] drug overdoses
3] excessive antihypertensive treatment
4] anaphylaxis
5] peripheral vasodilation
b) low cardiac output
1] myocardial, pericardial & valvular heart disease
2] cardiac arrhythmias
3] pericardial tamponade
4] increased pulmonary vascular resistance
a] pulmonary hypertension
b] pulmonary embolus
c] positive pressure mechanical ventilation
c) NSAIDs* alter glomerular hemodynamics & raise the blood pressure threshold for prerenal azotemia
3) renal vasoconstriction
a) cyclosporine A
b) vasopressors (norepinephrine, epinephrine, phenylephrine)
c) amphotericin B
d) hypercalcemia (increased ionized Ca+2)
4) renal hypoperfusion
a) cyclooxygenase inhibitors
b) ACE inhibitors
5) renal vascular disease
a) renal artery stenosis
b) renal arterial thrombosis
c) renal embolic disease
6) hyperviscosity syndrome (rare)
a) multiple myeloma
b) macroglobulinemia
c) polycythemia
Epidemiology:
- more common in elderly [3]
Pathology:
1) stimulation of sympathetic nervous system
2) stimulation of renin-angiotensin-aldosterone axis
3) increased renal tubular Na+ reaborption (proximal tubules & distal tubules)
4) increased plasma ADH -> increased water resorption in the distal renal tubules
Clinical manifestations:
1) orthostasis
2) hypotension
3) signs of dehydration
4) signs of 3rd-spacing may be present
5) oliguria
6) signs of extracellular fluid volume depletion are absent in 50% of patients [1]
Laboratory:
1) urine osmolality > 500 mosm/kg
2) urine Na+ < 20 meq/L
3) fractional excretion of Na+ (FENA) <1%
- diuretic use may result in a high FENA
4) increased urine creatinine
5) microscopic evaluation of the urine is unremarkable
Management:
1) optimize volume status
a) normal saline for volume depletion
b) treat underlying congestive heart failure
c) normalize extracellular fluid volume
- diuretics if indicated
2) discontinue offending pharmacologic agents
3) treat hypercalcemia
a) loop diuretics
b) volume repletion
c) AVOID thiazide diuretics (enhanced renal tubular Ca+2 resorption)
Related
acute renal failure (ARF)
glomerular filtration rate (GFR)
hypercalcemia
renal artery stenosis (RAS)
General
azotemia
References
- Medical Knowledge Self Assessment Program (MKSAP) 11, 15, 16, 18.
American College of Physicians, Philadelphia 1998, 2009, 2012, 2018.
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1266
- Geriatric Review Syllabus, 7th edition
Parada JT et al (eds)
American Geriatrics Society, 2010
- Geriatric Review Syllabus, 8th edition (GRS8)
Durso SC and Sullivan GN (eds)
American Geriatrics Society, 2013
- Macedo E, Mehta RL.
Prerenal failure: from old concepts to new paradigms.
Curr Opin Crit Care. 2009 Dec;15(6):467-73.
PMID: 19855270
- Parikh CR, Coca SG.
Acute kidney injury: defining prerenal azotemia in clinical
practice and research.
Nat Rev Nephrol. 2010 Nov;6(11):641-2
PMID: 20981121