# Math question.

1. Your patient is receiving a Lidocaine drip of 1.0 g/500 cc fluid. If your drop factor is 15 gtts/cc, what rate in cc/hr should the infusion run to deliver 2 mg/m?

I found this question online. I know the answer is 60 cc/hr but I am not sure how to figure this question out. Please help.

Thanks.

Joined: Jan '04; Posts: 466; Likes: 29
Registered Nurse; from US
Specialty: 6 year(s) of experience in Infectious Disease

3. I need some help here to! I thought I would see if I could still do this kind of stuff.... But as I see it
1g/500cc = 1000mg/ 500cc = 2mg/1cc

the drip is set for 60cc/hr then the pt get 120mg/hr if you divide this by 60 minutes you get 2mg/min Right???????
D 2mg/min X Xcc/hr
H 2mg/cc 60min

Is this the correct formula used here????
4. try it this way

cc/hr = 500cc/1g X 1g/1000mg X 2mg/1min X 60min/1hr = 60cc/hr
5. Quote from alexillytom
your patient is receiving a lidocaine drip of 1.0 g/500 cc fluid. if your drop factor is 15 gtts/cc, what rate in cc/hr should the infusion run to deliver 2 mg/m?
by dimensional analysis (the best way to do iv problems, by my way of thinking):
you want to end up with a fraction (or ratio) of cc per hour, so you are going to set up a series of fractions to multiply together to manipulate the labels, cancel out repeated labels, and end up with the labels you want. the math falls into place, believe me!

first of all, the drop factor on your tubing is a red herring and information that is not needed. you are being asked to give an answer in cc/hr so the drip factor of the tubing is an insignificant fact.

here is the setup:
2mg / 1min (given rate of infusion) x 500cc / 1 gram (given dosage on hand) x 1 gram / 1000mg (conversion factor for the dosage on hand) x 60 minutes / 1 hour (conversion factor for minutes to hours for the infusion rate) = 60,000 cc / 1,000 hours (after canceling out all duplicate labels in numerators and denominators and performing the math) = 60cc/hr (final answer after simplifying terms)
6. Quote from daytonite
by dimensional analysis (the best way to do iv problems, by my way of thinking):
you want to end up with a fraction (or ratio) of cc per hour, so you are going to set up a series of fractions to multiply together to manipulate the labels, cancel out repeated labels, and end up with the labels you want. the math falls into place, believe me!

first of all, the drop factor on your tubing is a red herring and information that is not needed. you are being asked to give an answer in cc/hr so the drip factor of the tubing is an insignificant fact.

here is the setup:
2mg / 1min (given rate of infusion) x 500cc / 1 gram (given dosage on hand) x 1 gram / 1000mg (conversion factor for the dosage on hand) x 60 minutes / 1 hour (conversion factor for minutes to hours for the infusion rate) = 60,000 cc / 1,000 hours (after canceling out all duplicate labels in numerators and denominators and performing the math) = 60cc/hr (final answer after simplifying terms)

da (dimensional anaysis) is the best way to do these problems. you just have to know the conversion factors for what you're given. after that, it's a piece of cake!!
7. I've just come into a program as a transfer student and have never heard of dimensional analysis before. Can anyone recommend a good text that can walk me through learning it? I have to ace these next medication exams. One I can do like a 90% but the other has to literally have NO errors! HELP! HELP! HELP! I'm so NOT good at this.

Thanks!
8. Quote from petite06
i've just come into a program as a transfer student and have never heard of dimensional analysis before. can anyone recommend a good text that can walk me through learning it? i have to ace these next medication exams. one i can do like a 90% but the other has to literally have no errors! help! help! help! i'm so not good at this.

thanks!
i don't have a book recommendation for you, but here are some links where you can read and learn about it:

http://www.wwnorton.com/chemistry/tutorials/ch1.htm - click on "1.4 dimensional analysis". it is an interactive program that explains da using animation rather than video in what i thought were very simple terms. also includes several problems you can try your hand at which are not chemistry related but utilize the concepts of da.

http://www-isu.indstate.edu/mary/tutorial.htm - from the indiana state university a "basics" page on medication math with explanations on how to do a number of different types of medications problems (including iv problems), conversions and dimensional analysis with links to lots of practice quizzes.
9. Quote from Petite06
I've just come into a program as a transfer student and have never heard of dimensional analysis before. Can anyone recommend a good text that can walk me through learning it? I have to ace these next medication exams. One I can do like a 90% but the other has to literally have NO errors! HELP! HELP! HELP! I'm so NOT good at this.

Thanks!
I never even heard of dimensional analysis(DA) until a few months ago. But i bought a book called "DIMENSIONAL ANALYSIS FOR MEDS" by Anna Curren, and now i could do dosage calculations in my sleep(using DA). I would recommend the book for self study
10. Daytonite, Andy and any others!

How do you know which formula will be best for setting up these problems? Daytonite mentioned that for IV the DA is the best. Are there others to consider though?

I learned a bit of DA back in my basic math class before Algebra, b/c our instructor knew there were a few nurses to be in the class and gave us a bit of prep. I'm learning some in Chem but in no way do I feel proficient at them yet.

I'm considering taking a seperate pharmacology class before the actual nursing program to be a boost. But I'd like to know if there's anything I can look over or learn before I actually go! I'm one of those that practically likes to sit in classes as refreshers not learn, b/c I fear that class will speed ahead and I'll be lost. From what my GPA states that's never the case, but I do feel like I struggle more than others to keep my high GPA...although I love the feeling when I finally figured out something that was not making sense...it's like YESSSSSSSSSSSS!

I'm going to look into that book that Andy mentioned...I aleady have Schaum's math for nurses and I play with that sometimes...but it also makes no sense since I don't really understand the drug calcs yet.

TIA
Michele
11. Well, thanks for the tips on the DA. I just hate the math component because I can typically do it on paper but having to put it into play in real life I'm still slow at. It just makes me feel so stupid. So, I've gone through the two texts I have about the drug calc and only one has a short few pages on DA. I went ahead and ordered the book someone recommended to me. I found it for less than \$7 brand new! What a steal!!!

Someone mentioned taking a Pharm class before. My personal opinion along with several of my friends is that those classes are so dry. My recommendation is to take the money you would spend on that class and apply it to a couple different Pharmacology texts. I would start more with a "..made incredibly easy" style book. The way you want to approach it is to learn it by categories. If you try a different way, I think it's worthless. I know everyone I knew that went through the Pharm class I did felt it was useless. Then I would invest in the same style of drug calculations books and practice every day before you go into nursing school and every day while in school...at least 30 mins a day. The more you practice, the more you'll feel better. Make sure that one of your drug calculation books have dimensional analysis so that as you get into higher levels with more complicated problems, you can work through them. Don't make the same mistakes I've made and not do something every day.
Good luck. I look forward to the receipt of this book. I'm gonna prove I can do this!!!!!!!!!!!!!!!!!!!!!If IT KILLS ME DOING IT
12. Thanks everyone. I can't believe I drew a blank on that question. This is my third semester in nursing school. I can usually figure these kinds of problems out with no problem. We have to get a 90% on the quiz. Thanks to you guys, especially Daytonite, who reminded me about the wonderful dimensional analysis method, I got a 100%.
13. Quote from kittyhawk
How do you know which formula will be best for setting up these problems? Daytonite mentioned that for IV the DA is the best. Are there others to consider though?
Michelle. . .in clinical practice I actually use the formula Dose Desired / Dose on Hand X Amount on Hand. I've heard it stated different ways, but this is the way I was taught it 32+ years ago. It never fails me for most things, except when it comes to calculating drip rates. Then, I sometimes have to use dimensional analysis because of having to bring in conversion factors.

Actually, the problem the OP presented can also be worked with the formula as long as you know how to work with complex fractions where you have fractions in the numerator and fractions in the denominator and then apply your conversion factors. You have to work a lot of problems to decide what works best for you. The above formula works fast for me in clinicals. When I have a vial of 250mg of Solu-Medrol and the doctor only wants 150 mg of it given IV push, I need to know how much to draw up and give to the patient. I can't be standing at the med cart for 10 minutes figuring this out. I have to calculate on the back of my "brains" (report sheet) or a piece of paper toweling quickly that 150 (dose desired) divided by 250 (dose on hand) X 2 mL (amount the 250mg is reconstituted in) = 1.2ml and that I have to draw up 1.2cc of the solution to give to the patient. (I actually carry a compact calculator the size of a credit card in my pocket for this.) This kind of calculation is so common I probably performed it a couple times a day. It works for Heparin drips too because I did it enough for them.

You cannot learn med calc by doing a few problems. Like any math teacher will tell you, and why they assign endless homework problems, you have to work problem after problem after problem until you are sick to death of them. And, when you think you know what you are doing, change the numbers on the problems and work them all again. Work them backwards and forwards so no matter what information you are given in a problem you can get to the answer being sought.
14. Quote from Petite06
Well, thanks for the tips on the DA. I just hate the math component because I can typically do it on paper but having to put it into play in real life I'm still slow at. It just makes me feel so stupid. So, I've gone through the two texts I have about the drug calc and only one has a short few pages on DA. I went ahead and ordered the book someone recommended to me. I found it for less than \$7 brand new! What a steal!!!

Someone mentioned taking a Pharm class before. My personal opinion along with several of my friends is that those classes are so dry. My recommendation is to take the money you would spend on that class and apply it to a couple different Pharmacology texts. I would start more with a "..made incredibly easy" style book. The way you want to approach it is to learn it by categories. If you try a different way, I think it's worthless. I know everyone I knew that went through the Pharm class I did felt it was useless. Then I would invest in the same style of drug calculations books and practice every day before you go into nursing school and every day while in school...at least 30 mins a day. The more you practice, the more you'll feel better. Make sure that one of your drug calculation books have dimensional analysis so that as you get into higher levels with more complicated problems, you can work through them. Don't make the same mistakes I've made and not do something every day.
Good luck. I look forward to the receipt of this book. I'm gonna prove I can do this!!!!!!!!!!!!!!!!!!!!!If IT KILLS ME DOING IT
I like Math for Nurses. It has helped me a lot! GL!