Dosage Calculations HELP!

[ohmylove]

I have a math test next tuesday and I was practicing from my worksheet and I came across this problem and I don't know how to start it out if anyone could help me that would be great!! :)

The IV is infusing at 30 gtt/min. The Drop factor is 20 gtt/mL. The IV label reads 500 mL 5% dextrose and 0.45% sodium chloride. The IV had been infusing for 1.5 hours when you came on duty. How much longer does the IV have to infuse?

my formulas:

flow by gravity :

mL/hr x gtts/ml

_______________ = gtts/min

60

flow by infusion:

total mL ordered

_______________ =mL/hr

Total Hours

The answer was 4 hours but I'm not sure how to get that

[Michaelxy]

Let's do this with Dimensional analysis. If you have not learned this method I suggest you learn it, love it as it is a great tool for such problems.

Dimensional analysis saves you from having to remember formulas, and whenever you are given starting information and know what you want to end up with, dimensional analysis will get you there. Shall we begin?

First ignore the part 5% dextrose and 0.45% sodium chloride as this is a ploy used in test to make the problem seem more complicated and we will not be using it in our calculations. Instead of 5% dextrose and 0.45% sodium chloride we have 500ml of stuff.

So we are given Drop rate of 30 drops per minute and we are also given the drop factor of 20 drops per ml. Okay so for some silly reason we have to change drop to gtt, so let's do that. We have 30gtt/1 min and 20gtt/1 ml. We almost have all that we need to finish. Almost, We were given the starting amount of 500 ml of stuff.

I bet your thinking about the 1.5 hour thing, as you should but we will get to it in a bit.

Start with what we have. 500 ml stuff/? hours x 20gtt/1 ml x 1 min/30gtt x 1hr/60 min =5.55 hrs of stuff

Lets break that down.

We know that we have 500 ml of stuff and we need to know how long it will last.

500 ml is how many drops or gtt? 500ml x 20gtt/1ml = 10,000 drops. So 10,000 drops at 30 drops per minute is about 333 minutes and if we convert the minutes to hours we have around 5.5 hours. Which we got using the line line equation.

500 ml stuff/? hours x 20gtt/1 ml x 1 min/30gtt x 1hr/60 min =5.55 hrs of stuff

Knowing that the IV had started 1.5 hr earlier we simply subtract 1.5 hr from 5.5 hr total and we end with 4 hours.

If you are not familiar with Dim Analysis then I am sure I confused you and apologize. See my DA link above. It is a great tool that I think all nurses would benefit from learning it As there are no formulas to remember.

Sorry if I was not helpful.

[STLPN]

At 30gtt/min with a drop factor of 20gtt/ml will give you 1.5ml/min 1.5x60 will give you 90ml/hr. Infusing 500ml@ 90ml/hr. 500 divided by 90 = 5.5 to infuse. The IV has already been running for1.5 hours 5.5-1.5=4

[afox]

Thanks for posting that website- I just looked over it, and it contains a lot of helpful information and reminders! :)

[ohmylove]

Sorry I haven't had the chance to thankyou! But yes, this did help out very much! My test is on Tuesday it's very nerve wrecking cause we have to get a 90% or better or we have to drop out of our medication administration lab :x! Wish me lots and lots and lots of luck. Thank you again!

[STLPN]

good luck !!! keep studying

[ohmylove]

I got an 100%!!! :) wooo hooo