Master the board step 3

Nephrology 10
Acute Renal Failure
The first step is to evaluate whether the renal failure is prerenal (perfusion),
renal (parenchymal), or postrenal (drainage).
··
Clues to the renal failure being of short duration are the following:
--
Normal kidney size
--
Normal hematocrit
--
Normal calcium level
··
Chronic renal failure will have the following effects:
--
It makes the kidneys smaller.
--
With renal failure of more than 2 weeks, the hematocrit will drop from
loss of erythropoietin production.
--
Calcium levels drop from the loss of vitamin D hydroxylation (i.e., activation).
Prerenal Azotemia
Any cause of hypoperfusion will lead to renal failure:
··
Hypotension, generally with a systolic pressure < 90 mm Hg
··
Hypovolemia from dehydration or blood loss
··
Low oncotic pressure (low albumin)
··
Congestive heart failure: You can’t perfuse the kidney if the pump doesn’t
work.
··
Constrictive pericarditis: You can’t perfuse the kidney if the heart cannot
fill.
··
Renal artery stenosis: Although the systemic pressure may be high, the
kidney thinks the body is hypotensive because of the blockage.
251