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!!

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.

AliNajaCat

1,035 Posts

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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