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Great job! I too was really nervous about my dosage calc test. Passed it, so I'm happy. I think dimensional analysis is great. Once I figured it out I realized how simple it is compared to the other methods. Plus, I don't have to remember a formula.
This is how I do dimensional analysis. By the way, this is a question from the book Dosage Calculations Made Incredibly Easy!, which I highly recommend if you (as in, the person in the online abyss reading this right now) are having problems with dosage calculations.
A patient is to receive 50 mcg of levothyroxine (Synthroid). The drug is available as 200 mcg per 5 ml. How many milliliters should the nurse prepare?
First, figure out what the the question is asking. How many milliliters? Start setting up the equation.
Now, what quantities does the problem give us?
50 mcg and 200 mcg/ 5 ml
I always set up the equation putting what I need to end up with first. So, since I need to end up with milliliters I will put milliliters (5 ml/200 mcg)right after the equal sign.
ml = 5 ml/200 mcg
Now I have to figure out how to get rid of that mcg since I only need to end up with ml. The only quantity I have left is 50 mcg.
ml = 5 ml/200 mcg x 50 mcg
Cancel out the mcg and do a bit of math and you get 1.3 ml.
It's just easier for me to remember that if I need, say, mg when I'm all done then I need to write mg = ___ mg/_____ x _____.
So it doesn't matter what you're calculating, whether it's drip rates, number of tablets, or dosages. Just start with what you need and on the other side of the equal sign start with that same unit. So if you need gtts/min you write out gtts/min = ___ gtts/______ x _____.
We just had our first day of 2nd year and, of course, had the beginning of the quarter math quiz. Our school only requires and 80% but I got 100%. Completely blanked on the very first question because I forgot to look at this particular type of question before school started. I have no issues with dimensional analysis and could honestly do this math stuff in my sleep, but I had to work backwards to figure this problem out. Fortunately I had the right answer.
wordsofmymouth, that is exactly how I do it to. Dimensional Analysis is where it's at. I get very intimidated by other methods that might involve fractions divided by fraction. Freaks me out. DA makes it so easy.
Our dosage calc tests are pass/fail and you fail if you get 2 wrong. You do get a 2nd shot at the exam later on. If you fail, you fail the entire semester. It's harsh, but in the end we could kill someone if we get it wrong.
Our entire class, for the first time ever in the history of our school, passed our test this semester!