drug math HELP!!

francine79 · Aug 16, 2004

What size is the tubing you are using to infuse the solution. The amount of medication received depends on the size of the tubing that is being used.

francine79 · Aug 16, 2004

Ok, I figured it out the tubing size by working backwards.

For #1:

Your tubing is microtubing (60gtt/ml). You need to first find out the rate that your solution is going at. To do that you need to convert your 20 gtt/min to ml/hr.

Since you are using microtubing: you would divide 60 gtt/ml by 60 min to come up with 1 as your drop factor.

Then to convert to ml per hour your would multiply 20 gtt/min by your drop factor (1). This results in 20 ml/hr.

Next, you need to find out how many mg/ml of dopamine there is in the 250 ml bag of D5W. To do that:

400 mg / 250ml = 1.6 mg/ml

Next, you need to find out how many mg of dopamine is being infused each hour:

Your solution is running at 20 ml/hr so multiply that by 1.6 mg/ml = 32 mg/hr.

Then to find out how many mg/min:

32mg/hr / 60 min = 0.533 mg/ min.

then convert 0.533 mg/min to mcg:

0.533 x 1000 = 533.3 mcg/min

#2

First you need to find out how many mcg/hr the doctor has order:

4 mcg/min x 60 = 240 mcg/hr

Then you need to find out how many mcg/ml there are in the solution:

There are 1000 mcg/mg so the solution contains 1000 mcg/250 ml.

To find out mcg/ml divide 1000mcg / 250 ml = 4 mcg/ml.

Then to find out the amount of mcg you need to deliver per hour:

60 min x 4 mcg/ml = 240 mcg/hr

To find out the rate you need to set the solution you need to divide 240 mcg/hr by 4 mcg/ml = 60 ml/hr.

Again the tubing is microtubing since the problem doesn't say. So to convert 60 ml/hr to gtt/min you need to come up with your drop factor constant by dividing the microtubing value (60) by 60 min = 1.

Multiply the 60 ml/hr x 1 = 60 gtt/min.

I know it's kind of confusing. Yes, 15 gtt does equal 1 ml. But when it comes to IV calcluations you need to know your tubing size because that will affect the amount of solution that is given to the patient.

tdg_rn · Aug 16, 2004

Are you using the Delmar Dimensional Analysis Book? That is the same one I am using in my program. Not to contradict the last posts (they are right) but this may be a little easier - especially if we are in the same book.

The first thing to remember is that 15 gtt does not always equal a mL. A MICRO drip set uses 60 gtt = 1mL. The whole thing with Dimensional Analysis is that everything is supposed to line up simply and quickly so think of the questions like this:

Your first one you need to know mcg/min so:

mcg/min = 1000mcg/1mg*400mg/250mL*1mL/60gtt*20gtt/1min

It looks a little clearer when written instead of typed but when it's all said and done you should be able to cancel out every UNIT except the one that you are trying to get in your answer then do the multiplication.

Your second question you are needing gtt/min so:

gtt/min = 60gtt/1mL*250mL/1mg*1mg/1000mcg*4mcg/1min

The only real trick in those questions is that you remember you are dealing with a MICRO drip set up. Don't assume that 15gtt/1mL. If you were dealing with a MACRO drip set up it could be 10gtt, 15gtt or 20 gtt and the information would have to be given.

Double check to see if I typed everything in...

Does that help?

Terence

tdg_rn · Aug 16, 2004

Oh yeah...what about the dancing thing? :)

Browneyedgirl · Aug 16, 2004

Thanks!!!!!!!!!....The tubing size was not listed in the problem.

I am using the Delmar, 2nd edition. These are problems 4 and 9 respectively from page 260.

Uhmmmm...the dancing? Dancing in my jammies NOW. :-)

chris_at_lucas_RN, RN · Aug 16, 2004

"no message" is too short....

It sure it Monday!

:rotfl:

chris_at_lucas_RN, RN · Aug 16, 2004

obviously you have to know if you are using micro- or macro- drip sets, that part you can't "figure out."

but generally, if you will start with what you have, and move in the direction of what the question is asking, using ratios (or fractions, or equivalents--however you best conceptualize it), you can recall that every time you multiply to get closer to your goal, you are not changing anything, you are just multiplying by "one."

for example, you have a dosage in mg per kg, and you want mg per lb, if you multiply your mg/kg by kg/2.2 lb (which is one, right?) you now have mg/lb.

it makes more sense if you can make the ratios with one value "on top" and the other "on the bottom," and then cancel out, just like multiplying fractions in grade school.

good luck with that med math. i had a hard time with it (although i aced algebra and thought calculus was fun, i had to repeat all but my last med math quiz because of the -2 = fail thing).

i discovered my stress was getting to me and i was "overthinking." then i figured out all it was, was ratios, and i started to just line those puppies up and canceled out stuff, and voila! the answer appeared. i was a much happier nursing student.