new student who needs ALOT of help with dimensional analysis!!

Focker, CRNA · Feb 1, 2006

1000mg/1000mL = 1mg/1mL

200mg/4hrs = 50mg/hr = 50mL/hr

50ml/hr = 50ml/60mins = 50ml/3600secs = .014mL/sec

That should be the correct answer unless I misunderstood your question, I assumed that they wanted the entire 200 mg given continuously for a total dose of 200 mg over 4 hours (since asking you to calculate a drip rate would make no sense if you bolused it every four hours). I have no idea what dimensional analysis is.

upstateRN · Feb 1, 2006

Hi I really hope that someone can help me. I'm a new student in nursing and haven't taken a math class in a long time and have never done dimensional analysis. I was wondering if there is an easy way to understand it and plus the answer to this question. A post-operative patient is to receive 200 mg of intravenous antibiotic every 4 hrs. a 1.00 litre bag of IV solution contains 1000 mg of antibiotic. What drop rate (in seconds) of IV solution is required for the patient to receive the correct dosage of antibiotic? thanks so much for your help.

Hi there.

Dimensional Analysis is not quite that bad. you just have to work through a few of the problems.

As long as you understand what's going on within the problem itself, the dimensional analysis will just fall into place and help you achieve your end result.

Basically all the middle terms/units will cancel out and allow you to get your answer i the correct units.

take your example:

A post-operative patient is to receive 200 mg of intravenous antibiotic every 4 hrs. a 1.00 litre bag of IV solution contains 1000 mg of antibiotic. What drop rate (in seconds) of IV solution is required for the patient to receive the correct dosage of antibiotic? thanks so much for your help.

there's always extra fluff in there.

just read through and ask yourself:

What do they REALLY want?

and then

WHAT do they GIVE ME?

what they really want is the drop rate (ml/Sec)

your patient is to receive 200 mg of IV antibiotic every 4 hrs (200mg/4hrs)

so start with that:

200 mg/4 hrs

you now need to get rid of the mg so what they give you is that there are 1000mg of medication in 1liter (1000 ml)

so now add 1000ml/1000mg next in the dimensional analysis.

then you must convert the hrs into seconds.

step by step..

this becomes

(1 hr/60 mins) x (1 min/60 s)

putting this all together,

you get

ml/s = (200 mg/4hrs) X (1000 ml/1000mg) X (1 hr/60 mins) X (1 min/60s)

doing units first, the milligrams cancel, as do the hrs and minutes.

that leaves you with ml/s which is your desired unit.

math-wise: go through and cancel/reduce what you can:

the 1000/1000 cancels, leaving you with 200/4 X (1/3600)

cancel out the 2 zeros on top and on bottom, leaving you with 2/4 x (1/36).

if you finish out the math, it becomes 1/72 = 0.013888, rounded, becomes 0.014 ml/s

i hope that helps.

i know it's hard since it's on the comp, but if you write it out on paper it should make a little more sense.

tridil2000, MSN, RN · Feb 1, 2006

Hi I really hope that someone can help me. I'm a new student in nursing and haven't taken a math class in a long time and have never done dimensional analysis. I was wondering if there is an easy way to understand it and plus the answer to this question. A post-operative patient is to receive 200 mg of intravenous antibiotic every 4 hrs. a 1.00 litre bag of IV solution contains 1000 mg of antibiotic. What drop rate (in seconds) of IV solution is required for the patient to receive the correct dosage of antibiotic? thanks so much for your help.

____________

LOL

this is an insane scenerio! there's NO way you administer meds in seconds!

the drip rate is 50 ccs and hour and you'd set a pump for that. pumps are now used for everything, especially a liter bag with 1 gram of a med mixed in it! imagine if that liter was free flowing and accidentally poured in a pt? pumps operate on ccs per hour (maybe some are minutes) but in no way seconds!!!

ree-nee · Feb 1, 2006

eventhough dimensional analysis centers on math and algebra, it is mostly introduced and taught in the first few chapters of basic chemistry to convert one unit of measurement to other..ie moles to molecules, kelvin to celcius, densities etc. i guess it is assumed that if you are in chemistry then you have basic algebra skills under your belt to comprehend the concept of dimensional analysis which you can use anywhere.

my advice would be to check out a chemistry book from the library and see if that kinda helps. ive always thought it was better explained there than in algebra.

its a long drawn out lesson of using proportions and cancelling common units of measurement:

example:

how many inches are in 10 miles?

ask yourself what distance proportions do you know of that would help?

i know 12 inch = 1 ft. i know 1 mile =5280 ft.

now you can start with pieces of info you are given.

10 miles x 5280feet x 12 inches= 633600 inches

[color=white]____________1 mile[color=white]___1foot

since this is on computer its a bit harder, but the units in purple cancel (cuz one is on top and one is on bottom), the units is green cancel for the same reason and the unit of measurement that is left hanging out alone with nothing to cancel with is inches. you multply everthing across the top and multiply everthing across the bottom. divide the top answer by the bottom answer.

keep in mind that this is the simpler version of a problem--its gets way tougher. the basic idea is the same though.

hope this helped a bit.

:)

Daytonite, BSN, RN · Feb 1, 2006

here are a couple of links to help you out. the problem as you have written it is not complete. there is infomation missing from it that allows any of the posters to give you an answer. the only conclusion that anyone can come to is that the dose you are to give, which is 200mg, is contained in 200ml of iv solution. you are missing a time element. over what period of time is the dose to be given? also, what is the drop factor of the tubing you are to use? or, is a pump being used?

http://www-isu.indstate.edu/mary/tutorial.htm - this page has an explanation of dimensional analysis and how to set up medication problems using this method.

http://www.accd.edu/sac/nursing/math/mathindex2.html - basic tutorial on getting started with pharmacology math. at the bottom of this home page is a drop down box where you link into any of the following subjects: common conversion factors/equivalencies, common abbreviations, ratio and proportion, iv problems, titration problems, and pediatric pharmacology math.

http://www.accd.edu/sac/nursing/math/default.html -- the start page of this pharmacology math tutorial presented by the nursing department at the san antonio college. by clicking on the "go figure" button you can access quizzes on basic med calculations, iv, pediatric and ob med calculations. the quizzes all have answers. follow the directions.

http://home.sc.rr.com/nurdosagecal/ - med calc for nurses from central carolina technical college. explanations and quizzes (with answers) on the following subjects: measurements, conversions, oral dosages, parenteral dosages, iv flow rates, dose by weight, iv push meds, critical care iv's and tube feeding.

dbroyles · Feb 1, 2006

There is a wonderful book called "Dimensional Analysis for Meds" by Anna M. Curren - (purple cover with a picture of a syringe). This book saved my life during pharm. It takes you back to simple math, then helps you step-by-step work through all dosage calculation problems(i.e., I.V., peds, oral, syringe, etc.) I strongly suggest investing in this book and keeping it with you at all times until you feel comfortable in calculating any and all medication dosages. Not all facilities work with pumps. . . some are still using drip factor. Lots of luck.