Med Math Examples - page 2

by ♪♫ in my ♥

7,308 Unique Views | 16 Comments

For reasons of which I'm not really sure, I'm inclined to start a thread populated with med math examples. I'm going to pose some questions and then work them through. I'm going to utilize an equation editor so that they're very... Read More


  1. 2
    Quote from ♪♫ in my ♥
    Agreed... some people have difficulty, however, with the idea that numbers and units are algebraically equivalent, hence the decision not to skip any steps at all.
    I've found that a lot of my cohort were never taught that whole concept of "multiplying by one" -- they would try to "memorize the formulas" for each type of calculation, without ever having anyone explain *why* the formulas are set up the way they are in the first place. Once I teach them the concept of "equal to one", then all of a sudden they realize that they never had to memorize ANY big fancy formulas at all -- just multiply by one over and over until you get to the answer you need (yes, that's an overly-simplified way of looking at it, but often times they just need to RELAX, take a breath, and realize that it really is NOT as complicated as they are trying to make it!).

    Quote from ♪♫ in my ♥
    My personal approach is to do a quick-solve in my head and then work it out in full detail to ensure that I get the same answer... internal consistency increases the likelihood of accuracy.
    I always tell people to "do a sniff test" after finishing the formula. If you're putting in hundreds of drips per minute -- something's probably wrong. If you're infusing over a liter an hour -- something's probably wrong. If you're only doing 1-2 drips per minute -- something's probably wrong. If you're injecting less than 0.1mL -- something's probably wrong. If you have to use more than one vial of something to draw up what you need (or if you need more than one 10mL syringe), something's probably wrong.

    Also, they should run the formula backwards once they find their answer, to make sure the math works in both directions. Number of drips per minute times number of minutes to find total volume infused. If it doesn't work out to the original amount, then you missed something somewhere!
    GrnTea and ♪♫ in my ♥ like this.
  2. 2
    Yes.. the "sniff test!!"

    In engineering analysis classes we were always instructed to check for the "reasonableness" of the answer. I think a lot of people would do well to spend time with a stopwatch, an eye dropper, measuring spoons, a small measuring glass, a large measuring cup, and a kitchen scale... trying to get a sense of "reasonableness."

    You're also right about the "freaking factor"... that is, people becoming flustered and confused because they do not understand the simple underlying concepts... the internal distraction is a killer.
    brillohead and GrnTea like this.
  3. 3
    Quote from ♪♫ in my ♥
    Yes.. the "sniff test!!"

    In engineering analysis classes we were always instructed to check for the "reasonableness" of the answer. I think a lot of people would do well to spend time with a stopwatch, an eye dropper, measuring spoons, a small measuring glass, a large measuring cup, and a kitchen scale... trying to get a sense of "reasonableness."
    As in, "no, it's not reasonable to think that a newborn baby weighs 10kg"?


    Quote from ♪♫ in my ♥
    You're also right about the "freaking factor"... that is, people becoming flustered and confused because they do not understand the simple underlying concepts... the internal distraction is a killer.
    Most people see dosage calc questions like this, I think:

  4. 1
    Quote from brillohead
    I've found that a lot of my cohort were never taught that whole concept of "multiplying by one" -- they would try to "memorize the formulas" for each type of calculation, without ever having anyone explain *why* the formulas are set up the way they are in the first place. Once I teach them the concept of "equal to one", then all of a sudden they realize that they never had to memorize ANY big fancy formulas at all -- just multiply by one over and over until you get to the answer you need (yes, that's an overly-simplified way of looking at it, but often times they just need to RELAX, take a breath, and realize that it really is NOT as complicated as they are trying to make it!).
    I agree so much! Many teachers never both to explain why formulas are the way they are, which would lead to an understanding of what you're looking for, what info you need, and how to go about solving it. As a result, so many people get caught up in memorizing formulas, but as soon as they come across a problem that is just slightly different, they have no idea what to do and panic. However, if they had the understanding, you can apply the concepts over any med dosage problem.

    Another issue is that there is almost always more than one way of going about a mathematical problem, so the methods vary between teachers (and nurses). As a result, people get inconsistent lessons and get confused. Again, just having an understanding of the problem rather than getting caught up in formulas is the key, because then you can see the logic behind anyone's methods!
    brillohead likes this.
  5. 0
    Okay, I'm' reviving this - my prof gave us a huge medmath worksheet to have done before the first day of class. I read the chapter in the book at it was absolutely no help. If anything it just made me more confused. Got together with a few other students and got a few done but I am confused to say the least. Just ordered a copy of calculate w/ confidence, which should arrive later this week. But in the mean time, help!

    A patient who has hypertension is to receive Nipride 50 mg in 250 mL D5W to
    infuse at 3 mcg/kg/min IV drip. Pt weighs 50 kg. How much Nipride would each mL of the IV mixture (D5W 250 mL + Nipride 50 mg) contain?____________
    Using an infusion pump, a nurse should set the flow rate at how many mL/hr? _______________________
  6. 0
    Hi ebinbrooklyn,

    To figure out the ml/hr you should have start by converting the 50mg to mcg, =50000mcg

    The formula should then look like the following:

    250ml x 50kg x 3mcg x 60minutes. (60min is not in the question but in the formula always)
    -—------------------------------(divided by)
    50000mcg

    I'm sure you can figure out the math.
  7. 0


Top