Ratios and blood glucose

Discussion in 'General Science & Technology' started by Tiassa, Jul 17, 2009.

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  1. Tiassa Let us not launch the boat ... Valued Senior Member

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    Tonight I got ... well, it wasn't exactly a crash-course in diabetes, as I got hung up trying to read a 1952 paper on renal function during and after a diabetic coma, but still.

    Anyway, someone somewhat removed from me (of no acquaintance whatsoever), dropped into a diabetic coma, and I found myself scrambling across the internet trying to advise a friend on what was going on. Not that I'm an expert; I just happened to be awake and have access to the internet.

    Anyway, the number was shocking to me at first, because I vaguely remember my last bloodwork, and, well, the first blood glucose update I got tonight involved what seemed unbelievably big numbers. And then I started looking things up. Turns out they were bad, but not as huge as they were.

    But I came across a strange conversion issue, and it turns out my math was pretty close. If I'm impressed, it's because math and I are not closely acquainted. Other than that, no, it's not impressive that my math was right. It was fairly basic, since I had a general conversion factor from the Mayo Clinic. And then, of course, I later found a page that had the numbers I needed, but, hey, I got to do some math.

    As to the question, though: In the United States, we express blood glucose and some other statistics as a ratio of mg/dL. Apparently, in the rest of the world, they use mmol/L. On the one hand, I wonder if this isn't just another example of Americans refusing to hop on the bandwagon with everyone else.

    To the other, I had to look up the definition of a mole.

    And, you know, I don't doubt that moles and millimoles have plenty of useful, wonderful applications that I simply wouldn't complain about. I'm not contesting the fact or utility of a mole. But in the case of blood sugar, I just don't get it.

    Milligrams per decilitre is fairly easy for me to grasp. I can almost envision the quantity ratio in my mind. But millimoles per litre is completely abstract; it seems you're essentially counting atoms. Like I said, I have no quarrel with moles and millimoles in and of themselves. It's just that in this case it seems like a really complicated ratio.

    So I'm wondering why. Is it more exact? Is it simply a matter of consistency of scientific terms?

    Anyway, in case anyone is interested, the patient is apparently stabilizing. The first number I got was 917 mg/dL (≈51.1 mmol/L). Like I said, that dropped my jaw, since I remember my own blood glucose, a few years ago, being down near 100. But I learned that normal blood glucose should be <140 mg/dL (<7.8 mmol/L), and that 1,800 mg/dL (≈100.285 mmol/L) is a general threshold figure for diabetic coma. So the number I got represented a declining blood glucose level. Eighty minutes later, I got another update, and the number had crashed to 515 mg/dL (28.86 mmol/L). I can't say how long the patient had been down before I got that first number. We are, of course, hoping for the best, but while the patient is stabilizing in what seems good course, I have no idea when she crashed, so there are no damage estimates.

    But yeah. I turned to a friend (our man Asguard; many thanks) for some insight into diabetic comas, and that's when I discovered we had a conversion issue to resolve. So now that I've done a little basic arithmetic, I'm curious as to why we Americans use a different standard, and why the rest of the world uses what seems like a really complex ratio.

    Or maybe I have it backwards. Maybe ours is more complicated and unwieldy, but like I said, it seems like you're essentially counting atoms with mmol/L.

    Thanks much.
     
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  3. Asguard Kiss my dark side Valued Senior Member

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    In the case of BGL i think its just a convention, there are lots of silly conventions in med, one which bugs me the most is Blood Pressure vs Respitory effort.

    BP is expressed as mmHg (mm of mecury) as im sure most people would be awear if they had been to an old GP who had one of the old school mecury bar BP's (now we use a pressure guage). Anetheologists on the other hand describe the amount of pressure used to ventalate someone as mmH2O. This means if you need to balance these 2 numbers (which is sometimes nessary) its not a straight conversion (to be honest the second one is WAY over my head, i just happened to be doing a placement in ICU when a med student was and the doctor was discussing a pts condition with both of us)

    my main guess for the use of mMol\L would be that its has to do with blood concentration which is measured in mMol\L. For instance a solution of 5% glucose and 0.9% NaCl (normal saline) have the same molarity as blood even though there amounts (in contrast to the level of water) is different. There for a solution of 5% glucose wont alter a pts fluid levels. For instance if i gave a pt a solution of 10% glucose because they were having a hypoglucimic event this might correct the hypogluycemia but would ALSO cause a fluid shift into the vascular space causing cells (including red blood cells) to shrivel up.

    On the other hand if i was to give 1% glucose the cells would swell up and burst as the fluid shifts OUT of the vascular space because of the osmotic pressure gradients.

    For most people (myself included for the most part) working out the molarity of a substance isnt important just knowing how to aplie it is. For instance a BGL meter will come up with a level of 3.8 (or whatever) and its only tonight when tiassa gave me the reading with units atached that i actually went and looked up what those units actually WERE. Its irrelivent for the most part
     
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  5. Asguard Kiss my dark side Valued Senior Member

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    ops i made a mestake, lung pressures are cmH2O NOT mmH2O
     
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  7. S.A.M. uniquely dreadful Valued Senior Member

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    Molarity is gram molecular weight of a substance in one liter of a solution [a 1M solution]. Since molecular weight differs between solutes, molarity evens out or standardises these differences by allowing us to compare across elemental entities [or what we call atoms, molecules, electrons]

    e.g.

    http://en.wikipedia.org/wiki/Mole_(unit)

    Consider also that what we consider as "standards" [weight volume density] are subject to temperature pressure and things like gravity.

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    Last edited: Jul 20, 2009
  8. Super Dominican Banned Banned

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    My nephew Vin have diabetes, we drink him purple drink when he feel woosy.
     
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