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Thumb abduction while measuring blood pressure!

2K views 13 replies 6 participants last post by  Dr.NickRiviera 
#1 ·
NOTE: this is a USMLE Consult-"inspired" question, so look away if you plan on using USMLE Consult as a measure of your progress.


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A 48-year-old man is very anxious about having his blood pressure taken. While the blood pressure is being taken in the left arm, the thumb adducts into the palm. Which laboratory test findings is most likely present?

A. Decreased artierla pH
B. Decreased ionized calcium
C. Decreased serum PTH
D. Decreased serum albumin
E. Decreased total serum calcium
F. AIDS
 
#10 ·
So i'll try to write it, if i get smth wrong ... just correct :D

the man is very anxious. it is like us during exams. we get perioral numbness and all the stuff :D

what really lies behind it is decrease in only free ionized Calcium. how it happens:

while breathing fast we loose too much CO2 -> this leads to the respiratory alkalosis. in this case there is increase is blood PH so decreas in H- concentration. Body is trying to get hydrogen ions from the proteins in the blood. in the normal PH the proteins have COOH groups, but in case of deacresed plasma H they donated their own hydrogen and give COO- form.
this negative charge has to be equalized. So plasma FREE CALCIUM ( ionized one ) binds to the proteins.
generally there are two fractions of Ca in plasma: I. Free - unbound to the albums and II. Bound fraction.

In our patient the fraction of free Ca decreased -> to bind with the albums i.e. bound fraction is increased... hence there is no change in TOTAL PLASMA CALCIUM.

decreased free calcium gives typical signs. for example Chvostek sign:

" It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped at the angle of the jaw (i.e. masseter muscle), the facial muscles on the same side of the face will contract momentarily (typically a twitch of the nose or lips) because of hypocalcemia" from wikipedia
http://en.wikipedia.org/wiki/Chvostek_sign

Same happened here. due to the hypocalcemic state the nerve is easily exited -> thumb adduction.

Hope this helped :)
 
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#12 ·
" It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped at the angle of the jaw (i.e. masseter muscle), the facial muscles on the same side of the face will contract momentarily (typically a twitch of the nose or lips) because of hypocalcemia" from wikipedia
http://en.wikipedia.org/wiki/Chvostek_sign

Same happened here. due to the hypocalcemic state the nerve is easily exited -> thumb adduction.
Ah this makes sense. But the question is stating Trousseau's Sign then not Chovstek's.

And also, just out of curiosity, would USMLE give such a question with so little detail? The question just says that the patient is anxious, but it requires us to assume that hes hyperventilating so he has resp alkalosis and developed signs of hypocalcemia .. just coz he came in to get his blood pressure checked ?:rolleyes:
 
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