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The major role of the
kidneys is to regulate salt and water balance
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This is achieved by
filtration, secretion and reabsorption
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The kidney is divided
into 3 functionally distinct parts – cortex, medulla and pelvis
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The medulla is the site
of urinary concentration, using a oxygen and energy hungry
countercurrent multiplier NaCl pump
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The hypoxic environment
of the medulla makes it vulnerable to ischemic damage
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Renal self preservation
is achieved by autoregulation and tubuloglomerular feedback
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Oliguria is most
commonly due to hypovolemia, and is termed “acute renal success”
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Acute tubular necrosis
results from ischemic injury to the medullary cells
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Acute renal failure is
characterized by inability to concentrate the urine or reabsorb sodium
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Anuria is post-renal
obstruction until otherwise proven
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Oliguria is hypovolemia
in surgical patients until otherwise proven
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Other causes of renal
failure are: glomerular damage (glomerulonephritis), tubular obstruction
(pigment nephropathy) and interstitial inflammation (interstitial
nephritis or edema)
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The best way to manage
perioperative renal failure is to prevent it:
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Be aware of patients
at risk: pre-existing impairment
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Avoid nephrotoxins
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Make sure the patient
is fluid loaded
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Maintain renal
perfusion pressure (with catecholamines)
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Avoid agents that
increase medullary oxygen consumption (vasodilators and osmotic
diuretics).No specific agent has been shown to prevent or curtail
peri-opeative renal injuries
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Where cross clamps
are applied the duration should be minimized
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