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Volume to be Infused by Drip Factor

Date: 07/02/2003 at 14:49:23
From: Lisa
Subject: Volume to be infused by drip factor

A patient is to receive 1440 milliliters of fluid in 24 hours. The 
drip factor is 15 drops per milliliter. The formula for drops per 
minute is:

   volume to be infused x drip factor
              time in minutes

The patient should receive about how many drops per minute?

I want to pass an entrance exam for a nursing program, but I have 
never been very good in math.

Date: 07/02/2003 at 23:15:41
From: Doctor Peterson
Subject: Re: Volume to be infused by drip factor

Hi, Lisa.

You've been given the formula, so you only have to apply it to your 
problem. Let's think about what it means.

The volume to be infused is the total 1440 mL the patient is to get.

The drip factor is the 15 drops per mL, determined, apparently, by the 
equipment and/or the solution.

The time in minutes is the total time over which the given amount is 
to be administered. This is 24 hours; but how many minutes is that? 
Well, every hour consists of 60 minutes; so 24 hours is 24 times 60 
minutes. This gives 1440 minutes. (It looks as if the numbers have 
been chosen artificially to make the problem as easy as possible for 

Now you just have to plug those three numbers into the formula:

  1440 mL * 15 drops/mL
      1440 min

We could actually multiply 1440 by 15 and then divide by 1440; but we 
can save time by "canceling" the 1440, because multiplying 15 by 1440 
and then dividing by 1440 takes you right back where you started, at 

I included the units in the formula because that is a very useful way 
to check that you are doing the right thing. We can treat the units 
as if they were numbers (or, better, variables, if you are familiar 
with algebra). Multiplying mL by drops/mL cancels just as the 1440 
did, leaving drops in the numerator; dividing that by minutes gives 
drops/min, which is just what you want to get.

For more on this method, see

   Unit Conversions, Unit Cancellation

I'd like to make a comment, and I hope it will not offend you, but 
motivate you. Your question scares me, because I don't want nurses who 
can just barely do this kind of calculation to work on me! Also, the 
fact that a high school could graduate a student who can't do this 
means our schools are practically worthless. I hope you will recognize 
the seriousness of this lack on your part (whoever is to blame for 
it), and work really hard at these problems if they let you into the 
program. Don't just figure that you got by and can ignore math in your 
work; make sure you fully understand how to work with units, because 
it will someday be a matter of life and death.

- Doctor Peterson, The Math Forum

Date: 07/08/2003 at 11:55:00
From: Lisa
Subject: Thank you (Volume to be infused by drip factor)

I would like to thank you for helping me with this problem.  I also 
want to comment on what you said to me. I agree with you. I told my 
mom the exact same thing. I walked away from high school (20 yrs) ago, 
knowing nothing. Now that I am older I want to learn and make 
something of myself, and with your help and comment, I will be a 
productive person. Again I thank you. I will remember you when I 
become a nurse.  :-} Sincerely, Lisa Cabassa

Date: 07/08/2003 at 12:09:26
From: Doctor Peterson
Subject: Re: Thank you (Volume to be infused by drip factor)

Hi, Lisa.

Thanks for writing back. I like the attitude!

I might add that I made that comment because I see far too many 
questions just like yours from people IN nursing or pharmacy school, 
and it really does make me worry about the state of our country. I 
recently suggested to a teacher asking about integrating the topic of 
health into a math class that she should do it in a way that would 
scare the kids into realizing that math can be a matter of life and 
death. Knowing that you are several years out of school mitigates the 
issue a bit in your case, but the reminder is still appropriate.

- Doctor Peterson, The Math Forum
Associated Topics:
Middle School Measurement
Middle School Terms/Units of Measurement

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