Med Math

AliNajaCat · Feb 27, 2017

You don't need dimensional analysis for this problem. You have correctly divided the liter by 125 to discover that it will be used up in eight hours. If all they are asking you is, "When does the next one go up?" and you can see that eight hours from 0800 is 1600 (or 4pm), then you're done. If they want you to tell them when the second one will be done, you then divide the second liter by 80 and see that it will be done in ____ hours, right?

Let me take this opportunity to repeat my rant about memorizing equations (such as dimensional analysis). I know they can be helpful but ONLY IF you can see when you need to use them.

Test writers know that many people will take a question and pull all the numbers out of it and jam them into an equation. Then they put choices in the multiple choice that will result from somebody having done that, even erroneously, because they know their audience. Alas, a portion of that audience can't read questions critically to see that some of the facts listed have nothing to do with the answer sought. Example:

Give miraclecillin 1gm in 250cc 0.9%NaCl over one hour. Miraclecilin comes in a vial labeled "Add 5.6cc for 2gm/6cc." Your IV tubing has a drop factor of 15gtt/cc. How fast do you set your pump?

If you can't read that and realize that the question stem says you're going to give 250cc in one hour, and so the only possible answer is "250cc/hr," then there's a lot of trouble in med math in your future. :) If you have set up a dimensional analysis with 2, 6, 15, 1, 0.9, and 250 somewhere in it ... you're in big trouble.

Editorial Team / Admin · Feb 27, 2017

Kaweah, you've now started three threads within the last 24 hours on med math questions. Perhaps you need to seek out tutoring from your school or meet with your instructor, especially as mentioned in another thread that dimensional analysis is required (which doesn't make sense as not all questions require its use).

SopranoKris, MSN, RN, NP · Feb 28, 2017

I'm going to suggest the book "Math Attack: Winning the Pharmacology Math Battle" by Karen S. Champion to you. It explains in very conversational language 4 different ways to approach med math problems. It's very easy to understand and takes the guess work out of answering med math questions. You seem to have quite a few posts related to dimensional analysis. I think you will find that this book explains how to use dimensional analysis in a way that makes sense.

By the way, the question that was posed is not really conducive to using dimensional analysis, because it's asking you to pinpoint at what time a 2nd liter will be hung. There's really no "set up" for dimensional analysis here. Just simply dividing 1000 mL by 125 mL/hr = 8 hours. Then you would need to add 8 hours to 0800. The addition cannot be a part of the dimensional analysis, which is all multiplication.