Medical Dosaging

Nursing Students Student Assist

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Okay there has to be an easier way to do this because my eyes are crossing and Im getting extremly confused:

Heres the question

Order 4mcg/kg/min, the IV bag has 800 mg of Dopamine in 500 ml of D5W. The patients weight is 70kg. The drop factor is 10 drops = 1ML. What will the flow rate be in drops per hour?

So what I was told to do which is confusing the hell out of me because there is so many numbers in this.

MY WORK: 70 KG X 4 MCG X 1MG X 500 ML X 10GTT

_________________________

kg x 1000mcg x800mgx ml

Im so beyond confused..my teacher confused the hell out of me and makes this much more harder than what its supposed to be. But my answer is 105 drops per hour.

SECOND QUESTION:

oRDER 5MG/KG IF THE CHILDS WEIGHT IT 38 LBS, HOW MANY MG WILL THE CHILD RECEIVE.

MY WORK : 38/2.2=17.27kg x 5mg/1kg = 86.35

86.35 Miligrams just does not make any sense to me!!

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
I was taught that with dimensional analysis, I can multiply all of my numerator figures then divide by all of the denominator figures -- no need to round at each step of the analysis -- however if i do that, I get 86.36

It's unclear to me how we are supposed to know when we have to round at each step (as Esme12 seems to suggest) versus being allowed to simply multiply all numerator figures then divide by all of the denominator figures (which has worked for every other drug dosage problem I have ever had to do).

I only rounded once....the weight. The lengthy explanation was to show how to get tot he answer step by step. I will only round once in any calculation usually the weight and final answer. The OP had already had it all laid out and was confused in the first post so I showed step by step.....it doesn't matter how long it take to get there you just have to get there. Of course I do calculations much faster but that is not the way to teach.

go to the websites I mentioned they are very good.

clinical calculations for nurses is a good book lotsa of good practice...you'll get, once you find a way stick with it, i personally like dimensional analysis, it's a good way to see you mistakes. practice makes perfect, believe me you will figure it out, it will all come to you eventually.

:) second semester student

i'd recommend do all your multiplication and division then round, early rounding within the problem or truncating can lead to a very different answer

if you can save rounding to the very end, then thats the best, and 86.36 should be within a reasonable margin of error

I agree that it's within a reasonable margin of error, but on the computerized exam that I took where I had to type in a numerical answer, only one answer was correct, there was no reasonable margin of error. So how would I know if I should round the weight conversion (as Esme12 did) or if it's OK to do all of the multiplication/division and then round.

Esme12 gets 86.5 by rounding at the weight conversion.

I get 86.4 by rounding at the end.

The computer will only accept one of these answers and it's unclear to me how I would know which process the computer is expecting.

I don't really have a problem with setting up any of these problems. I have done a lot of them. My problem is more with how to get the "right" answer that a computerized test wants so that I don't miss easy points because of the difference between 86.5 and 86.4 being the answer.

:cry: iam for lack of a better word..screwed!...i cant even begin to understand this....what in gods name am i going to do...i should just give up now...

thanks for posting this...shows me what i am in for

it looks more complicated than it is. da is based off of the basic formula,

(d/a)xq=x

where,

d= dose ordered , (4mcg/kg/min).

a=available strength, (800mg)

q=quantity of medication that has that strength (500ml)

in my example i just split up the conversions so it was clear where the numbers were coming from, traditionally in da, you do the conversions in the formula.

the one rule we have is that the units of measure must be the same we and this is where it gets messy

to start we need the dose, 4mcg/kg/min. the pt is 70kg, so we multiply 70 x 4 and get 280. the dose is 280 mcg/min

roughly the formula looks like this at this point,

((280 mcg/min)/800mg)x500ml=gtt/hr

however, the units of measure are not the same. the conversions we need to know are

1000 mcg = 1mg , 60 min = 1 hr, 10 gtt = 1ml

in relation to mcg vs mg, you can either divide mcg by 1000 or multiply mg by 1000, it doesn't matter. but anyway the formula becomes,

(280mcg/1) x( 1mg/1000 mcg) x(1/800 mg)x( 1/min) x (60 min /1hr) x (500 ml/1) x (10 gtt/ 1ml) =gtt/hr

now multiply, divide and cancel the units, if every thing is set up right the units on the left should match the ones on the right.

(280mcg/1) x( 1mg/1000 mcg) x(1/800 mg)x( 1/1min) x (60 min /1hr) x (500 ml/1) x (10 gtt/ 1ml) =gtt/hr

we have gtt/hr = gtt/hr , that a good sign we didn't miss anything

cleaning up the formula it looks like this,

(280) x( 1/1000) x (1/800) x (60 /hr) x (500) x (10 gtt) =gtt/hr

step by step we get,

280/1000=0.28

0.28/800=0.00035

0.00035 x 60/hr =0.021/hr

0.021/hr x 500 = 10.5/hr

10.5/hr x 10 gtt = 105 gtt/hr

there are usually 2 or 3 different ways to get the same answer.

When we started the program they gave us a big list of conversions to memorize, which included both of kg to lb conversions. The rounding rules are in our student hand books. We wouldn't round either of these (85.5, 86.35). I know my ATI books have a drug calculation section and think they only give the 2.2 lb conversion, but i would have to check.

I agree that it's within a reasonable margin of error, but on the computerized exam that I took where I had to type in a numerical answer, only one answer was correct, there was no reasonable margin of error. So how would I know if I should round the weight conversion (as Esme12 did) or if it's OK to do all of the multiplication/division and then round.

Esme12 gets 86.5 by rounding at the weight conversion.

I get 86.4 by rounding at the end.

The computer will only accept one of these answers and it's unclear to me how I would know which process the computer is expecting.

I don't really have a problem with setting up any of these problems. I have done a lot of them. My problem is more with how to get the "right" answer that a computerized test wants so that I don't miss easy points because of the difference between 86.5 and 86.4 being the answer.

For that you'd have to talk to the instructor and/or whoever wrote the exam to see when they rounded as well as what answer the expect in the box, and if they will let you "challenge" it if they rounded early and got 86.5 where as you rounded to the tenths at the very end and got 86.4. I once missed a question because the correct answer was "1.5" but myself and half the class put "1.5 ml" or "1.5 mL" or some variation, but the teacher when presented with the facts that the instructions were unclear gave us credit and changed the blackboard programing a wider range of correct answers as well as clarified in the instructions not to add units or round early.

Long story short, depends if its a standardized nursing test (HESI) or something your instructor has more control over (blackboard tests) and discuss what is expected, then you can always point back to, "but you said do it this way..." for tests the instructor controls.

For the standardized tests, to the best of my knowledge, round at the end to how many decimals the test question tells you to round too, the HESI's & NCLEX are very specific on what they want to see at the end (rounded to the nearest whole number, 10ths, 100ths, 1000ths place etc, and usually ask that you don't include units)

also rounding at the end from a math standpoint gets you closer to the correct answer, if you were to have rounded early on a longer problem, your answer could be off by more than 0.1 mg, and depending on the drug being given that could be an issue or could be no big deal

I checked, ATI uses the 2.2 lb conversion. The rounding rules according to ATI are that you round to the nearest hundredth if the answer is less than 1 and round to the nearest tenth if more than 1. This is of course in conflict with my NS math policy.

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

On computerized tests you won't find the answers to be A) 86.2 B)86.4 C)86.5 D) 86.5.(usually). I have always been taught that you round the weight to only one decimal point.....17.3.

Those web links I gave especially dosages/calculations for nursing students is an excellent site and has tons of practice questions.

Those web links I gave especially dosages/calculations for nursing students is an excellent site and has tons of practice questions.

I've done hundreds of practice questions and get 99.9% of them correct. But from time to time, I run across a weird one like this where, for an instructor graded exam, my answer would probably be fine but on a computerized exam, it would not.

I also have been taught to round weight to tenths, so if I was asked what is the equivalent weight in kilograms, I would answer 17.3 kg. But when it comes to problems where you're converting the weight along with other units of measure, I was not told that it's necessary to FIRST convert the weight and round to tenths and THEN do the rest of my dimensional analysis, so I find it perplexing how to be sure to get the "right" answer (rather than the "reasonable margin of error" answer) for the computerized tests.

Sounds like there isn't any way to be 100% sure and it will be on an instructor-by-instructor basis when it comes to computerized quizzes & tests. Thanks to everyone who has shared their opinions!

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

No there isn't..........crazy isn't it. Medicine isn't really an exact science. In the real world(out of school), technically it is difficult to give 86.4 so you would give 86 or 86.5. Sometimes, I might call pharmacy for the MD clarify if we collectively on a floor are having this kind of discussion. But I, personally, would give the 86.5 milligrams if it was not a liquid.

Good Luck in school Indy!

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