# help me calculate this problem.. - page 2

1. An infusion ordered of 2g in 500 mL is ordered at 60mL/hr 2g/500mL ???... Read More

1. Quote from EmilyEmily
2000mg/500mL x 3mg/60min

i get the wrong answer with this formula
Wrong formula.

2000mg/500mL = 4mg/ml. Your ordered dose is 3mg/min. How many mL/min is that? Take that answer and multiply by 60 and you'll have your flow rate per hour.

Perhaps set the problem up as a proportion problem to find the rate per min.

4mg 3mg
---- = -----
1mL X

Solve that... and you'll be 1/2 way to your answer, depending upon what flow rate (ml/min or ml/hr) is being asked.
2. Quote from EmilyEmily
2000mg/500mL x 3mg/60min

i get the wrong answer with this formula
Well look at the way you have this problem set up. Your answer is going to give you mg SQUARED over min x mL. That's no good. You're looking for mL/hr.

Your infusion rate is 3 mg/min not 3 mg/hr so you can't use 3 mg/60 min. To change the mg/min rate to mg/hr you multiply by 60 min/hr.

So 3 mg/min x 60 min/hr and the minutes cancel each other out to give you mg/hr.

Then you take your concentration, which you have already figured out and multiply it by that to give you mL/hr.
3. This student is why I hate teaching formulas to new students. They always take all those numbers and jam them in there and come out with something weird like mg^2 (mg-squared), which is meaningless but they don't get that.

Break it down into its component parts, solve them one at a time, and see what it is you're looking at, don't do it all at once.
4. Emily, I've been watching this thread but haven't had time to write out a detailed response.

I will share this, however: Don't try memorizing "formulas," try to understand the basic concept of what you're doing. If you learn the idea, there really are no "formulas," but just simple equations that follow from the information given.

Try to wrap your brain around the following concepts:

1) mass
2) concentration/dilution
3) volume
4) volumetric flow rate
5) mass flow rate
6) fundamental units and derived units
7) density

If I had to guess, you don't really understand one or more of these basic concepts which is why you're getting so confused.

If I were your tutor, we'd be certain that you could clearly articulate just what each of these mean and how they relate to each other. From there, the questions that you're trying to solve are quite simple.

I HIGHLY suggest you spend some time with a good tutor ASAP.
5. order is 3 mg (concentration)/ min (time)
available is 2,000 mg(concentration) inside 500 mL(volume)

cross multiply, answer will be = mL / min

2,000 mg is to 3 mg
as 500 ml is to X min.

500mL x 3 mg = 2,000 mg X

= 0.75mL / min... x 60 min (to make 1 hour) = 45 ml/hr

Go to the college library and check out Calculating with Confidence, or any Dosage Calc book, go through every chapter and they should give you both methods of solving the problem the way you like it
6. I know someone said don't memorize formulas but I do like a formula for this:

want
_____ x vol

have

want 3 mg/min
__________ so first this I do here is make sure my units of mass are the same. 2 g=2000 mg so it now reads
have 2 g

want 3 mg/min
__________ x 500= 3mg/min divided by 2000= 0.0015mg/min X vol (500)

have 2000 mg

0.015mg/min x 500mL= 0.75 mL/min

You need in hours so multiply by 60 (minutes in an hr)= 0.75x60= 45 mL/min