Medical Dosaging

Nursing Students Student Assist

Published

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!!

Up Vote Up Vote ×

For question 1, I got the same answer as you.

For question 2, it may be the conversion factor that is making you get a strange answer. You can say that 1 kg = 2.2 lb OR you can say that 1 lb = 0.45 kg (This is very similar to saying that 1 g = 1,000 mg OR 0.001 g = 1 mg (which results from dividing both sides of the first formula by 1,000 -- both of these conversion factors are equally valid.) To get from 1 kg = 2.2 lb, you divide both sides by 2.2 and get 0.45 kg = 1 lb. At one point in my research career it was convenient to learn all of these conversion factors in both forms so I'm accustomed to being able to use either in my day to day work.

When I used the first conversion factor (1 kg = 2.2 lb), I also got the same "strange" answer that you got. I chose that conversion factor first because when I used the other one on an ATI exam, I got the question wrong because it made my fill-in-the-blank answer off by 3 mg (297 mg vs 300 mg). However, when I repeated your question using the 1 lb = 0.45 kg, I got 85.5 mg which seems like a perfectly reasonable answer.

I'm not sure how you're supposed to know which conversion factor to use! I was told that in my program, we should use the 1 kg = 2.2 lb so that's what I plan to do, but it sure does give an odd answer for your question.

This is all pretty new to me. Maybe someone else will have some insight and I'll be saying "I didn't know that" when I check back tomorrow :)

Up Vote Up Vote ×

I did think of one other explanation for your 2nd question. Since both 38 and 2.2 each have only two significant digits, then your answer for converting from pounds to kilorgrams should also be only two significant digits (38/2.2 = 17) then when you multiply by 5, you'd get a nice integer answer. I guess I need to drag out my dosage calculation book and refresh my memory on where/if significant digits come into play.

Up Vote Up Vote ×

The info you have

Order 4mcg/kg/min

On hand 800 mg/500ml

Wt 70 kg

Drop factor 10

Xgtt/hr

------------

Dose order

4mcg/kg = xmcg /70 kg

X=280 mcg/min

________

What you have

800 mg/500ml =8 mg / 5 ml

1.6 mg/1 ml

_________

Conversion

1mg = 1000 mcg so, 1.6mg/1ml = 1600 mcg/ml

Also,

60 min = 1 hr

-------------------

How many ML do we need?

280 mcg/xml = 1600 mcg /1 ml

1600x=280

X=0.175 ml /min or 10.5 ml/h

-----------------

Gtt

0.175 ml / min 10.5 ml/h

10gtt/1ml

10 x 10.5 =105 gtt/hr

So yes it is 105 gtt/hr, it just when we do DA we place all the conversions in one formula.

question 2 depends on the conversion used, if you use the .45 kg/lb conversion the answer is 85.5, if you use 2.2lb/kg you get 86.35. The discrepancy comes fact that these conversions are not equivalent. Divide 1 by 2.2 and you get .454545 repeating. The real conversion is something like 0.45359....

Up Vote Up Vote ×
I did think of one other explanation for your 2nd question. Since both 38 and 2.2 each have only two significant digits, then your answer for converting from pounds to kilorgrams should also be only two significant digits (38/2.2 = 17) then when you multiply by 5, you'd get a nice integer answer. I guess I need to drag out my dosage calculation book and refresh my memory on where/if significant digits come into play.

In our program we round to the nearest tenth in adults and the nearest hundredth in pediatrics. I am thinking they meant for 0.45 kg/lb to be used in this problem.

Up Vote Up Vote ×
I am thinking they meant for 0.45 kg/lb to be used in this problem.

Why that conversion over the 1 kg = 2.2 lb??

On my ATI exams, you will get the "wrong" answer if you use 1 kg = 0.45 (even though in most research lab applications, the two could be considered equivalent if you were to keep it to 2 or 3 significant figures (which is pretty common))

Up Vote Up Vote ×

: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

Up Vote Up Vote ×

momtojosh, I swear this will make more sense when you see it in context. There are two main ways that I've seen nursing schools teach drug dosage calculations, so when you start your dosage calculations, you may find that some people's answers look like total gobbledy-gook because that isn't how you learned it. It will look like they're just writing down random numbers. Other answers will look more familiar because that poster will have learned the same method that you learned.

If you're nervous about the math being too hard, there are some good books out there that really walk you through step-by-step how to do the math. They even have intro sections that make sure you have the basics for adding, rounding, multiplying, percentages, fractions, etc so you can know that you're starting off right. If you have time, you could pick up one of those books and start doing a little of the math on your own time so that it will be much less intimidating later.

Up Vote Up Vote ×

first one i got the same answer, though in your work you left out the 60 minute/hour conversion, but apparently remembered it when you used your calculator as you came to the same answer

for the 2nd one, I also got a 86.36mg dose

out of curiosity, are you using dimensional anaylsis? makes these questions a heck of a lot easier cause you then just have to compare the units to make sure the ones you don't want in the end are cancelled out, it works wonders for dosage calculation and conversion math questions you see in nursing

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

please use the standard conversion factors and round up or down.

i use dimensional analysis.

there are certain essential parts to every equation.......

desired dose:

concentration:

volume on hand:

lb to kg:

looking for:

administration set up:

any conversions necessary?

ok......... first weed out unnecessary information then really look at the order itself

4 mcg/kg/min, iv bag has 800mg of dopamine in 500 ml of d5w. patient weighs 70kg. drop factor is 10drops=1 ml. what is the flow rate in drops per hour?

desired dose: 4 mcg/kg/min

concentration: 800mg

volume on hand: 500ml

lb to kg: 70kg

looking for: 4 mcg/kg/min

administration set up: 10drops=1 ml

any conversions necessary? yes mg to mcg

desired dose x volume on hand

concentration on hand = to be given/is available

first the question wants mcg, right?.......find out how many mcg/ml there is of dopamine

1000mcg x 800mg

1mg

how many mcg's if 1mg=1000mcg

800 x 1000 = 800,000mcg total in the bag

so now how many mcg's is on 1 cc

?1mcg x 800,000

500ml= which gives you 1600mcg/ml

so you now know that you have 1600mcg (of dopamine) per 1ml. you now need to know how many mcg/kg need to be given

desired dose x volume on hand

concentration = ml to be given

4mcg/kg is the desired dose how many kilograms is the patient? the patient weighs 70kg

4mcg x 70kg = 280 mcg/min

1minyou need to give the patient 280mcg/min

next you need to figure how much needs to be given per hour but we need that converted to mind, right? there are 60min in 1 hour. right?

280mcg/min x 60 min = 16800mcg/hr

1 hr

so you now know how much total needs to be give per hour per kg. now, how many ml/cc's per hour will need to be given to get 4mcg/kg/min. we know that there is a total of 16800 mcgs totalin 1 hour and there is 1600mcg per 1ml/cc16800 mcg/hr x 1ml = 10.5 ml/hr

1600mcg

but......if you need 10.5ml/hr and your tubing takes 10 gtts to equal 1ml

10.5 ml x 10 gtts = 105 gtts/hr.

1ml

order 5mg/kg if the childs weight it 38 lbs, how many mg will the child receive.

desired dose: 5m/kg

concentration: n/a

volume on hand: n/a

lb to kg: 38lb

looking for: mg/kg

administration set up: n/a

any conversions necessary? yes

desired x on hand

concentration/amt on hand = to be given/is available

there is 2.2lb per 1kg

38lb x 1kg = 17.27 round off to 17.3kg ( however your school showed you)

2.2lb

5mg/kg x 17.3kg = 86.5mg to be given

i am sure this is clear asmud.......please look at these they will help you alot!!!!

dosagehelp.com - helping nursing students learn dosage calculations - dosage question steps

[color=#660099]drug dose calculations - dave's ems

Up Vote Up Vote ×

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).

Up Vote Up Vote ×

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

Up Vote Up Vote ×
+ Add a Comment