# Meds / Math / reconstitution of powder HELP! - page 2

Does anyone know where to find this stuff? I don't understand how I am to determine the amount of liquid to use in reconstitution in the following problems: The physician orders 5,000,000 U of... Read More

1. First of all, V, everyone is correct! In order to do ratio/proportion, you must have three pieces of data. However, you can figure out a number of answers to this second question, depending on how concentrated you want it to be (assuming that there are NO instructions given regarding concentration of final solution, or if there is a range given but no one answer). This is basically what Rena suggested, but here is another possibility:

If you have 1000 mg of powder, you could dilute it with only 2.5 ml of fluid, giving you 400mg/ml concentration. Therefore, you wold need only 0.5 ml for injection (0.5ml in this example = 200 mg), which is a more reasonable amount that 5ml for IM administration.

A second example of an even MORE concentrated final solution is if you added only, say, 1.5 ml of fluid to the powder. This would give you your 200mg in a mere 0.3ml of fluid, which is also a small amount appropriate for an IM injection.

We learned the

desire
_______ x volume

have

method in school, where

Desire= the final concentration you want (in this case, 200mg)

and

Volume= the volume either present already or what you add to reconstitute (for this, see the two examples...the first one was adding a volume of 2.5 ml, the second added a volume of 1.5ml).

Does that make sense? Ultimately, to get these two possibilities that I worked out, I had to guess...kind of rule-out-mathematics, you could call it. With three variables, it's much easier to solve the problem.

The last thing I wanted to mention was that technically, though it does you absolutely no good at all in the long run or in real-life nursing, when you're solving a math problem on the test, especially on a *calculations* exam, you are really testing your ability to know the formula. Thus, the teachers can concoct whatever a**-whacked problems, made up uses (in this case, an IV-only medication that isn't even given IM form), tremendous numbers, teeny concentrations...whatever. (As SoFl mentioned, this medication may actually only be used in IV form, and these calculations would be pointless in real life, because her information says you should dilute much more than we have in our examples.) They're really testing to see if you understand the formula, because once you do, you can apply it to any situation, real or make-believe, to get the correct answer. It's kind of like the foundation for the math house you're building in your brain. ;>P Good luck!
Last edit by NICU_Nurse on Oct 26, '02
2. UPDATE -- I took the test today. 30 questions, if you miss more than 3 you have mandatory tutoring and then a retake of only 10 questions and can miss only one.

Many, many did not pass this test, more than half the class BUT THANKS TO THE HELP I GET FROM ALLNURSES.COM I passed IT!

I missed 2 questions, both for bonehead reasons but was able to work each one.

THANKS AGAIN
3. I read the vial as well............I remember in school some of those questions..............

WE were not allowed to use calculators either........

renerian

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