Bonus free practice exam #2 question #10 setup

by Jonn
(Willoughby, Ohio )

Can you show how to get the answer to this one?

Reply (Keith): Sure, Here it is:
An IV Drip is ordered to run at 4 gtt/min. It contains 875 mg of a drug in a 250 ml solution. How many mg will the patient receive per hour if the infusion set is calibrated to deliver 12 gtt/ml?

a. 0.70mg/hr

b. 16mg/hr

c. 70mg/hr

d. 160mg/hr


1. How many mL per Min.?
12 gtt/mL means that it takes 12 drops to equal 1mL.
4 gtt/min is how many drops will fall every min.
12 Divided by 4 = 3
So that's = 1mL every 3 minutes
(right?, since also 4 times 3 equals 12)

2. How much drug per mL?
875mg drug divided by 250mL = 3.5mg/mL

3. How many mL per Hr.
and 60 minutes (one hour) divided by 3 = 20

since one mL will drop 20 times per hour
(or every 3 minutes)

4. Add it all up.
Then 20 X 3.5mg/mL = 70mg/hr

This infusion device math is kind of confusing at first. Sometimes drawing a circle (representing a minute) and then drawing little drops in it helps to visualize it. I know that sounds a little silly, but it works for lots of people.

Comments for
Bonus free practice exam #2 question #10 setup

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Jan 10, 2012
@ Keith question on the # 10 workout
by: PT

I really appreciate your effort this site has been a huge help for my study. Now regarding your explanation(bonus # 2 question # 10) I am a bit confused on how the 3 became the minute since the unit on 12 is gtt/ml shouldn’t 3 take this unit and become 3ml/min? Need some explanation please.

Jan 03, 2012
PTCB test preparation
by: Elangovan Govindasamy

I'm so happy. Your PTCB practice quizzes are very useful.I'm working on them and I hope may be useful for my exam. I trust your site.

Nov 17, 2011
Tracking method
by: Anonymous

Wow that tracking method is amazingly simple! You just need to lineup the gtt/mg/ml to cancel each other out and have mg/hr as the product. Thanks for that!

Sep 03, 2011
Tracking Method!
by: Anonymous

I have used memorized formulas in the past, but came across a VERY helpful method shown on this site called the TRACKING METHOD. It is shown in a short tutorial video by someone who in my opinion has the most foolproof and successful way to handle flow rate and infusion problems.

Each bit of information given in the question is simply listed horizontally next to each other, with the desired ending units waiting at the far right of the list. Arrange the given units, adding a '60min/hr' in this case. The list of this problem looks like this:
4gtts/min * 875mg/250ml * 1ml/12gtts * 60min/1hr
When you multiply all this across it totals 210,000mg/3000hr, which siplifies to 70mg/hr.

It's so simple and it works every time!

Jun 02, 2011
IV Flow/Drop Rates
by: Anonymous

I am using the formula to find the gtts/min like this:(this is what we learned at school)

gtts/min= (vol. of fluid)/(delivery time in hours) x (drop set used) and all over divided by 60.

Can you use this formula in question #10 of the bonus practice test 2?

Thank you.

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