Blood Pressure Cuff Question

I was taught that a cuff that doesn't fit properly will give an inaccurate reading. Where I work we have three sizes and just today a student took a bp that was really low. When she was taking the cuff off I noticed that the cuff was the biggest we had. I took the bp with a better fitting cuff and it was fine. I discussed this with a co-worker (that has much more experience than me) and she agreed that the low bp was probably due to the wrong cuff size.

I believe they need to cover the middle 50-60% of the upper arm vertically, but more importantly, take a look at the cuff markings. Most all disposables and many permanent cuffs have a white line on them, as thus |__________| , and a small tick-mark on the other side of the cuff. The tick-mark or "artery arrow" must fall within the bracket of that line once the cuff has been wrapped.
The wrong size cuff will definitely give you a wrong reading. Small short cuffs read high, larger longer cuffs read low. Or for practical use, your standard cuff gives bigger people hypertension and stick people hypotension.
I think it has something to do with the physics of large volume/small volume bladders, pessure/volume gradients, in that short bladders don't meet, or fully compress the vessels in equal circumferece and pressure/volume gradient occurs quickly, while larger/overlapped bladders keep compression on longer at lower pressures.

Same principle as your car tire using 32psi while those two story high excavation trucks with six foot tall tires use about 6psi. It's all about percentages.

Or I could be totally wrong.
I hate math... lol.
rb

I was taught in school that to acurately take a BP, use a standard adult cuff if the pt was 100lbs or more and over 15yrs old, but use a large cuff if the pt weighed more than 150lbs. Of course, this theory should be adjusted if the pt is tall in stature (a person can weigh 175 lbs, yet be 6'2"-thereby having a "normal"-sized arm).

hello...im an LPN...im 19...graduated in 08....im working at a cardiologist office and love it....the doctor doesn't even ask me to do blood pressure...i know....strange...all he says to do are weights and EKGS...but the problem is this...ever since ive begun nursiing ive had trouble with blood pressures...hearing it...reading the number...i don't know exactly why?? i get a great stethoscope and can hear but yet still have trouble with it...but in my job there are opportunites to float to their other offices...i don't want to float and still have dificulty with blood pressures....i want to conquer this and do it like ive done it forever....please help someone!! TRULY NEED ADVICE...its starting to depress me...thank you

Practice, practice, practice.....at first I sucked at getting BP's, but after enough practice, I'm pretty good at em now.....and don't just practice in a quiet place....have background noise going too once you get the gist of it

Many times I find a cuff that will go around the arm on the top but by the time the cuff is on the bottom there is a ton of space. I call it the funnel arm. What do you suggest for those people?