Med Math Examples

[Music in My Heart]

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 easy to follow (the AN text editor really lacks in this regard). They'll show as images.

If you have specific questions that you'd like addressed, PM me and I'll use those for future additions to the thread.

Please refrain from posting problems in the thread simply because I'm hoping to keep it tidy and not end up with multiple people posting the same answers over and over and I'd like to avoid the mess that the text editor creates.

I'll also entertain chemistry or physics problems (meaning NOT explanations of concepts but simply worked out examples).

Here's the first one ~~~~~~~~

The physician orders an insulin drip at 8 units per hour. Your facility policy states that insulin must be mixed by placing 100 units in a 100 mL bag of NS. However, due to a recent shortage, you only have 50 mL bags of NS.

How much insulin do you place in the bag?

At what rate (mL/hr) do you set your pump?

How much insulin will the patient have received after 20 minutes?

[brillohead, ADN, RN]

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"?

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:

[Aeterna, BSN, RN]

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!

[ebinbrooklyn]

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? _______________________

[sMoLsNurse]

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.

[Esme12, ASN, BSN, RN]

Two sites that are excellent.....http://www.dosagehelp.com/......http://www.davesems.com/files/drug_dose_calculations.pdf