Working backwards on Dosage Problem

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Hey everyone. As the local chapter head of the "I can't do math at gun point" lodge, I need some help. I've pretty much taught myself the basic formulas for IV dosage calc. (no small miracle). However on this past Monday the prof. through a curve ball on an exam wherein she asked a question that didn't want to know the infusion rate (i.e mL/hr) but simply the total amount of time the infusion would take.

A friend tried to explain it to me via inverting fractions and the like, but it didn't stick. Any help? Thanks.

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Specializes in Nursing Home ,Dementia Care,Neurology..

So what's the question then?

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I'm sorry I wasn't clear. If I'm not looking to solve in terms of mL/hr, how do I solve for total time. Maybe I'm missing something obvious.

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Specializes in med/surg, telemetry, IV therapy, mgmt.

You have to do it by using dimensional analysis.

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Type the problem on here if you can remember it so we have something to work with to show you...:rolleyes:

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Specializes in Physical Rehabilitation, med-surg.
I'm sorry I wasn't clear. If I'm not looking to solve in terms of mL/hr, how do I solve for total time. Maybe I'm missing something obvious.

well, if you aren't solving for ml, then you have that as part of your problem information, right? When you're solving for ml, your time is known hr=1 hour or 60 minutes. ml/hr is the same as saying milliliters per hour.

so, if you have an IV antibiotic mixed in a 250 ml bag, how long will it take to infuse if you run it at 125 ml/hour. (Is that the kind of question you're talking about I assume??)

250 ml = 125ml

x.......... 1hr or 60 minutes

cross multiply and solve for minutes (you can also solve using hours, but just in case they throw out something weird, solve for minutes).

125x=250 times 60 min

125x=15000 min

15000min = 120min

125

120 minutes = 2 hours

The IV antibiotic will infuse in 120 minutes or 2 hours.

hope that helps.

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Thanks for the help everyone. I have an appt. to review the exam on Mon. and will copy the prob down to post here. I think I get the problem now though after your explanations and web resources. But just to be on the safe side I'll post the question. Thanks again.

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