Knowledge needed from medical professionals

[parishioner]

Moderators: I didn't know where to put this. Its not really first aid or emergency so...move at your discretion

To me, anyone with a basic grasp of physics or a general understanding of Newton's third law should be able to answer this question.

Ok...I just returned from taking my first nursing school test and I am livid (I am envisioning feeding a puppy chocolate and putting it in a microwave with a tin foil hat right now.....not really) because I know I missed a couple of questions but one in particular is driving me crazy.

Here is the gist of the question: An obese woman's blood pressure was taken using an adult sized cuff(too small). What will the outcome be?

I knew it was either going to be A. Falsely High
or B. Falsely Low

To begin, here is my understanding of how a Sphygmomanometer works. The cuff is wrapped around the arm about an inch above the brachial pulse. The cuff contains a bladder and when filled up with air the needle rises and occludes the artery. As the air is slowly released, the needle in the gauge decreases and the blood begins to flow back through the vessel. When listening with a stethoscope, the first sound you here is the blood coming back through and this is the measure of the maximum output pressure of the heart (systolic reading).

So, I remember reading the night before about how if the cuff is too loose it will yield a falsely high reading. The rationale being that you will need excessive pressure to occlude the artery.

This makes sense, right? If the cuff is loose, the bladder will have to fill with more air than usual to occlude the artery since it has all the extra room thus giving you a high reading. Easy stuff.

Remembering this, I thought to myself "Well, if a loose cuff yields a falsely high pressure than a tight cuff must yield a falsely low reading. If the cuff is tight, there is already an increased pressure on the artery to begin with, thus you will need less pressure (air) to occlude the artery giving you a False Low pressure." So I put B. Falsely Low.

It turns out I am wrong. The book states that a cuff that is too narrow will give you a Falsely High blood pressure stating you will need excessive pressure to occlude the artery.

So my question is is my brain not functioning properly or is there some kind of phenomenon that occurs with tight cuffs that I am not aware of? I mean, if the cuff is tight to begin with how in the name of all that is holy will you need excessive pressure to occlude the brachial artery?

[Icculus]

Ok I'm not a doctor, nurse or physics major but I'm wondering if its not a trick question in the wording. You just gave the gist of the question and not the actually wording so I'm just guessing here. Did the question actually use the word "narrow" You're logic seems spot on if the the length of the strap is too short and therefore too tight. What you quoted from your text though doesn't say to loose or tight but too narrow. Does the width/narrowness of the strap make a difference in the calculation separate from whether its too long (loose) or short (tight). Beyond that yeah, I'm sure going to want the opinion of a medical person. :)

I always hated those questions on tests that ate me up later because I knew I was right and they said I was wrong:)

[rickrock305]

i have absolutely zero medical training.

but it seems like common sense that a cuff thats too tight will result in a falsely high reading.

[parishioner]

Ok I'm not a doctor, nurse or physics major but I'm wondering if its not a trick question in the wording. You just gave the gist of the question and not the actually wording so I'm just guessing here. Did the question actually use the word "narrow" You're logic seems spot on if the the length of the strap is too short and therefore too tight. What you quoted from your text though doesn't say to loose or tight but too narrow. Does the width/narrowness of the strap make a difference in the calculation separate from whether its too long (loose) or short (tight). Beyond that yeah, I'm sure going to want the opinion of a medical person. :)

I always hated those questions on tests that ate me up later because I knew I was right and they said I was wrong:)

The book states if the cuff is too narrow for the extremity the result will be falsely high so to me that means it would be tight.

The loose cuff example is right after that one.

[stevenhyde]

Dont you have a book to look in?

You said you read about a loose cuff the night before. did the book say anything about a tight cuff?
maybe go back and re-read what you read. maybe you got it backwards.

If not, why dont you go show your teacher where in the book it says about a loose cuff, and ask whats up with the inconsistency. and why a loose cuff would do the same thing as a tight cuff.

Also, dogs can eat chocolate. Me and my ex came home once to find an empty bag of hershey kisses on the floor. no wrappers left, just a plastic bag.

It was an unopened bag when we left. Months later the dog is just as fine as he first day I met him.

[parishioner]

i have absolutely zero medical training.

but it seems like common sense that a cuff thats too tight will result in a falsely high reading.

I know. I shouldn't have actually tried to use my brain. I knew for a fact though that a loose cuff would result high.

[parishioner]

Dont you have a book to look in?

You said you read about a loose cuff the night before. did the book say anything about a tight cuff?
maybe go back and re-read what you read. maybe you got it backwards.

If not, why dont you go show your teacher where in the book it says about a loose cuff, and ask whats up with the inconsistency. and why a loose cuff would do the same thing as a tight cuff.

Also, dogs can eat chocolate. Me and my ex came home once to find an empty bag of hershey kisses on the floor. no wrappers left, just a plastic bag.

It was an unopened bag when we left. Months later the dog is just as fine as he first day I met him.

In my original post I stated what the book says about both scenarios. They both say Falsely High and both give the same rationale. I didn't have an opportunity to discuss it with my teacher since she had to leave immediately after the class to go work at the hospital. I am planning on it though.

[Erik 1]

Since the non-experts are replying here, and I'm as non-expert as any of you: it seems to me that a tight cuff will give a high reading because being too tight to begin with, it already has increased the pressure the gauge sees, then you pump it up and add more. A loose cuff, on the other hand, gives a high reading because you have to pump it up to a higher pressure to get the artery to stop flowing. Or maybe not.

[stevenhyde]

In my original post I stated what the book says about both scenarios. They both say Falsely High and both give the same rationale. I didn't have an opportunity to discuss it with my teacher since she had to leave immediately after the class to go work at the hospital. I am planning on it though.

Dur, thanks. i misread.
When you stated the second time about reading. i though i saw loose again. not narrow.

You didnt notice in studying before your test that the book said the same thing for both scenarios?

A tight cuff (i imagine) would have high pressure right from the start, simply cause the cuff is straining to be on an obese person.

so adding pressure when you use the cuff, would give a high reading.

A loose cuff, would need more pressure than normal just to fill up, so that will give a high reading too.
Maybe the book is right, and both loose and tight give a high reading.

...is there a midsized cuff?:confused:


dam, i type slow.
and i re-read stuff to much.

[chadbag]

Also, dogs can eat chocolate. Me and my ex came home once to find an empty bag of hershey kisses on the floor. no wrappers left, just a plastic bag.

It was an unopened bag when we left. Months later the dog is just as fine as he first day I met him.

Was it a female dog?

[bpw]

Hi,
I remember fondly many a test in Nursing school-not! Wait until you can take Boards. Anyway the cuff size is important because it holds the bladder. The bladder does not fill the whole cuff so if the cuff is too small the bladder does not compress equally around the arm.

I envision it that since the bladder sits over the artery it exerts pressure downwards to occlude it. If the cuff is too small then there is no bladder on the back of the arm. When the cuff is inflated the bladder fills up but some of the pressure is actually compressing the blubber on the back of the arm so the bladder pressure reads higher before it even has a chance to occlude the artery.

The cuff should also be wide enough to fill 2/3 the distance from the elbow to armpit if possible.

http://www.plus-size-pregnancy.org/lgbpcuffs.htm

has a nice discussion with some references.

brian

[parishioner]

it seems to me that a tight cuff will give a high reading because being too tight to begin with, it already has increased the pressure the gauge sees, then you pump it up and add more.

Pressure on the bladder doesn't effect the gauge, only the air inside, so, the gauge goes by how much air is in the bladder. I have one with me and I just pushed as hard as I could on the bladder and the gauge did nothing.

[parishioner]

[QUOTE=bpw;444640The bladder does not fill the whole cuff so if the cuff is too small the bladder does not compress equally around the arm.

I envision it that since the bladder sits over the artery it exerts pressure downwards to occlude it. If the cuff is too small then there is no bladder on the back of the arm. When the cuff is inflated the bladder fills up but some of the pressure is actually compressing the blubber on the back of the arm so the bladder pressure reads higher before it even has a chance to occlude the artery.[/QUOTE]

I can now see how it could give a false high for a fat person based on that but what about a person like me? What if you gave me a small cuff and because I have barely any blubber to compress on the back of the arm?

[parishioner]

Dammit. Im wrong. I hate being wrong. I think I understand now.

I think the relationship between loose and big and tight and small have created the discrepancy.

If you give a fat person a size to small, yes it will be tight but the bladder is not big enough therefore it will be falsely High.

If you give a fat person the correct size bladder, but wrap it tightly, I believe this would yield a False Low

When I read the question and it said adult sized cuff, this made me think it wasnt big enough therefore it is tight. So when I remembered the book talking about a loose cuff and it said false high, I thought a tight cuff would give a false low. I was thinking in terms of tight and loose and not taking into account the bladder size.

Thats a bullshit question. :p

[bpw]

"Thats a bullshit question"

Said that many a time myself. Interestingly though, on every test it seemed like everybody had their own idea on what was the BS questions were. The more advanced you go the worse it gets. I will stay with my MSN. I don't think I could stand to take the questions on doctorate level tests.
brian

[montanadave]

You think the questions NOW are bullshit, wait until you take the NCLEX. :D

And after blowing the dust off my old copy of Potter & Perry's Fundamentals of Nursing, bpw's rationale is correct.