Math Help

midwifemae · Apr 3, 2018

I'm not great with med calc but I feel like there is information missing. I use dimensional analysis and when I set it up we are missing the order. We know what we HAVE but we don't know what to give...this is making the mcg/kg difficult to calculate.

smf0903 · Apr 3, 2018

All the information you need is there. Do you have any idea where to start? If you can start/show what you've come up with so far then we'd be able to help guide you.

:)

chare · Apr 3, 2018

Whether you're a fan of DA or not, I think you're going to find that to be the easiest method to solve this type problem. If you haven't done so, you might want to review the following thread.

https://allnurses.com/pre-nursing-student/master-your-drug-1148937.html

bjwojcik · Apr 4, 2018

I know I always say too much, but here is my hint. You are starting off with 15 mL/h and have to somehow end up with mcg/kg/min. I like to change mcg/kg/min to mcg/(kg*min).

The ratios in the problem and the 100 kg will help you do this.

-Brad

bjwojcik · Apr 4, 2018

Hint 2: You will have to use your own ratios of minutes per hour and mcg per mg to solve this.

bjwojcik · Apr 4, 2018

I'm not great with med calc but I feel like there is information missing. I use dimensional analysis and when I set it up we are missing the order. We know what we HAVE but we don't know what to give...this is making the mcg/kg difficult to calculate.

Hi midwife,

The order is for 15 mL/h of the dopamine mixture. You don't have to give anything, just describe what is already being given in different terms.

-Brad

bjwojcik · Apr 4, 2018

Hey Cin808,

If you have been trying, but still can't figure it out, just let us know. You might get three different ways to solve it, but one of the ways will probably work for you.

Brad

bgxyrnf, MSN, RN · Apr 4, 2018

I typically use formula method to solve. I'm not a big fan of dimensional analysis.

I prefer to think of all these problems the way that a chemist does, as dilutions, proportions, concentrations, and flow rates... that is really all that dimensional analysis does but it circumvents thinking about what's actually happening in favor of simple unit consistency.

Dopamine is mixed as 200 mg of Dopamine in 250 ml of D5W infusing at 15 ml per hr. The pt weighs 100 kg. How many mcg/kg/min is pt receiving?

First, determine the mass concentration of the solution... that is, the mass of dopamine per unit volume of solution.

Next, determine the mass flow rate. You are given the volumetric flow rate with which you can calculate the mass flow rate utilizing the mass concentration.

Finally, determine the unit mass flow rate... that is, the mass flow rate per unit of patient mass.

You'll have to do a few unit conversions along the way in order to match your units of medication mass and time.

I won't rob you of the joy of first seeing the correct answer at the end of your own pencil but the number will be consistent with the renal dosage listed in the Davis Drug Guide.

cin808 · Apr 4, 2018

I haven't attempted to work it out yet but there is some good info here. My issue is that I am a visual learner. I have to SEE it in order to learn how to do it. If any part of the problem can be figured out using the formula method, that is what works for me. It makes the most sense and I've got that down pretty well. It would behoove me to learn how to solve using multiple methods and so I will need to practice DA. That's how I got through chemistry so I know I can do it. Plus, if you work it out two different ways, and get the same answer, you're most likely to be correct.

bjwojcik · Apr 4, 2018

See the attached PDF for my way of doing the problem. I hope that you try it on your own before you look at this.

Dopamine is mixed as 200 mg of Dopamine in 250 ml of D5W infusing at 15 ml per hr.pdf

midwifemae · Apr 8, 2018

Hi midwife,
The order is for 15 mL/h of the dopamine mixture. You don't have to give anything, just describe what is already being given in different terms.
-Brad

Thank you! I was totally overthinking it.