math calculation help

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hi!

I was wondering if someone could help me figure out how to set up this math equation. I have the answer provided but I am having trouble figuring out how to go about getting the answer on my own.

A solution of 10,000 units heparin in 500 mL D5W is to infuse via volumetric pump at 400 units/hr. Calculate the flow rate in mL/Hr. (answer is 20 mL/hour).

Thank you!!

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Specializes in Hospitalist Medicine.

When you have a med math question, always start with with what you want to end up with on the top of your fraction. In this case, you want to end up with mL/hr. You have 500 mL of D5W and that bag contains 10,000 units, so that is your first fraction (500 mL/10,000 units). Your pump needs to run at 400 units/hr, which is your second fraction. Multiply those fractions together and the units cancel out so you end up with 20 mL/hr.

500 mL X 400 units = 20 mL

10,000 units hr

Hope this helps clear it up. If you have a tough time with med math, I highly suggest the book "Math Attack: Winning the Pharmacology Math Battle" by Karen Champion. She explains 4 different approaches to solving med math problems in plain English.

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Another way to look at questions like this, before you even start in with equations, is to think in your head what they have already told you. So: If there are 10,000 units in 500cc, how many units are there in 1 cc? You should be able to do that in your head, or at least quickly on a piece of scrap paper.

10,000

______ = 20 units per cc, right?

500

So if you have 20 units per cc, how many cc will give you the 400 units you desire?

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