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Old 03-23-2012
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Sphygmomanometer Thumb abduction while measuring blood pressure!

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
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Old 03-23-2012
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Decreased ionized Ca
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it' E -
resp alkalosis -> H displaced from COOH groups of proteins -> COO- + Ca 2+ -> decreased Ionized Ca
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Old 03-23-2012
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Total serum calcium remains the same which makes due to the fact that calcium binds to albumin who had lost H ions. So, the one that its diminished is ionized calcium. (B is correct)
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Old 03-23-2012
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Quote:
Originally Posted by johnvega98 View Post
Total serum calcium remains the same which makes due to the fact that calcium binds to albumin who had lost H ions. So, the one that its diminished is ionized calcium. (B is correct)
yes yes .. it's B. total stays the same
I was in a hurry while reading Q
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Old 03-23-2012
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umm how do u know the old man has alkalosis?
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Originally Posted by theundead View Post
umm how do u know the old man has alkalosis?
he's very anxious -> i think he's breathing fast -> Resp.alkalosis
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Quote:
Originally Posted by beka-CTS View Post
he's very anxious -> i think he's breathing fast -> Resp.alkalosis
Tricky question...

Could someone explain this concept in more detail please ?
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Old 03-23-2012
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Quote:
Originally Posted by beka-CTS View Post
he's very anxious -> i think he's breathing fast -> Resp.alkalosis
thats very vague. It does not say he's anxious per se, only that he's anxious about getting his BP checked. It doesnt sound like his resp rate goes up as soon as he sees the BP cuff
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So i'll try to write it, if i get smth wrong ... just correct

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


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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Old 03-23-2012
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Quote:
Originally Posted by theundead View Post
thats very vague. It does not say he's anxious per se, only that he's anxious about getting his BP checked. It doesnt sound like his resp rate goes up as soon as he sees the BP cuff
i think that the fact that patient is very anxious about BP measuring is one of the clues to lead uss to the hypocalcemia ....


let's wait for dr.nick he'll clarify your doubts
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Quote:
Originally Posted by beka-CTS View Post
" 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 ?
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Quote:
Originally Posted by Hope2Pass View Post
Ah this makes sense. But the question is stating Trousseau's Sign then not Chovstek's.
Yes it's trousseau's sign in this this patient.
i tried to write smth different associated with case like this
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Old 03-23-2012
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Default answer = B

answer is B. decreased ionized calcium

this is a classical scenario of hypocalcemia that has the manifestation of Trousseau's sign.
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