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* nbme 7 -3-21
 #508245  
  stalinmbbs - 05/22/10 19:02
 
  21) A 14 year old girl is admitted to the hospital after sustaining injuries in a house fire. Her temp is 37.2 C (99 F), pulse is 115/min, respirations are 9/min, & bp is 100/65 mmHg. Physical examination shows second-degree burns over 40% of her body surface area. Labs show:

Serum:
Na+ : 138 mEq/L
K+ : 4 mEq/L
Urea nitrogen: 90mg/dL
Creatinine: 3.5mg/dL

Urine:
Na+ : 3 mEq/L
Osmolarity: 1220 mOsmol/kg
Excreted fraction of sodium:

which of the foll is decreased in this pt

a - collecting duct free water clearance
b- distal tubule potassium secretion
c - distal tubule sodium reabsorption
d- glomerular filtration
e - proximal tubue sodium reabsorption
 
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* Re:nbme 7 -3-21
#2111793
  drksingh - 05/22/10 19:05
 
  DD  
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* Re:nbme 7 -3-21
#2111836
  stalinmbbs - 05/22/10 20:07
 
  can u explain why

the answer given is different
 
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* Re:nbme 7 -3-21
#2111864
  drksingh - 05/22/10 21:29
 
  pre-renal azotemia
see the BUN:cr ratio is more than 20
so GFR should be decreased. other sr biochemistry is abnormal because the patient had 40% burns, so volume depletion.
 
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* Re:nbme 7 -3-21
#2112355
  drksingh - 05/23/10 16:16
 
  what is the answer, & its explanation
 
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* Re:nbme 7 -3-21
#2112388
  stalinmbbs - 05/23/10 17:22
 
  the answer given is AA

I am hoping some one will explain
 
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* Re:nbme 7 -3-21
#2112447
  needamiracle - 05/23/10 18:45
 
  I disagree with sanmarco's answer key for this question.

I took it online and got this question right; the answer is D as drksingh posted.

If you look at the lab values, osmolarity of urine is 1220 whereas Normal value should be around 700-900!!!

therefore, this indicates that the patient has a decreased GFR due to volume depletion because of burn trauma so kidney glomerulus is not functioning normally.
 
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* Re:nbme 7 -3-21
#2112464
  luckyflower - 05/23/10 19:10
 
  is NOT A):
collecting duct free water cl.is controlled by ADH!!! A decr.CD free water Cl=high ADH
 
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* Re:nbme 7 -3-21
#2112465
  luckyflower - 05/23/10 19:10
 
  is NOT A):
collecting duct free water cl.is controlled by ADH!!! A decr.CD free water Cl=high ADH
 
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* Re:nbme 7 -3-21
#2112466
  luckyflower - 05/23/10 19:11
 
  A decr.CD free water Cl=high ADH  
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* Re:nbme 7 -3-21
#2112467
  luckyflower - 05/23/10 19:12
 
  A decr.CD free water Cl=high ADH,usually driven by high serum osm, wich is NOT our case..
correct answer decr GFR, since this is prerenal azotemia..
Stalin, when did you schedule st1?
Best of luck, buddy!can you, plz, forward me NBMEs answers you have from 1-7? usmle_intern@yahoo.com
Thanks!
 
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