I have heard from a number of you that the math scares you. It
shouldn't and here are some math problems you will see at the CPNE.
If you can do the calculations here you should have no problems when
you get to your test site.
Med Math
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1) Example - Ordered: Lasix 40 mg IV push over 1 minute. Available: 80 mg in 1 mL. How
much will the nurse draw up?
Ordered
------------ x Volume of Liquid You Have = liquid required
Available
40 mg
------------ x 1 mL = 0.5 mL pushed over 1 minute
80 mg
To make math easy we know that the available dose is 80 mg in a 1 mL solution.
That would mean that you have 40 mg in 0.5 ml solution (half of 80 is 40 and half of 1 is 0.5).
Furthermore, you would have 20 mg in 0.25 ml (half of 40 is 20 and half of 0.5 is 0.25 and so
on.... (This last equation is not needed for this problem, I just wanted to show simple math)
I am not trying to insult anyone's intelligence but sometimes we get wrapped up in what
formula we need when the answer really is right in front of us using basic math.
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2) Example - Ordered: Polycillin 2 gms IV Q8 Hours in 500 ml normal saline bag. Infuse over 4
hours. Tubing drop factor = 10 drops per ml (gtts/ml)
Amount of Fluid x Drops Per ML (gtts/ml)
----------------------------------------------------
Time (60 minute intervals)
500 ml x 10 Drops Per ML (gtts/ml) 5000
---------------------------------------------------- = --------- = 20.8 (21 gtts/min)
4 hours x 60 mins =(240) 240
** The time of infusion is always calculated by 60 if it is in hours**
But what if the time to infuse is less than 1 hour ? Let's take a look below: _
_
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3) Example - Ordered: Polycillin 2 gms IV Q8 Hours in 50 ml normal saline bag. Infuse over 20 min.
Tubing drop factor = 10 drops per ml (gtts/ml)
Amount of Fluid x Drops Per ML (gtts/ml)
----------------------------------------------------------
Time (60 minute intervals)
50 ml x 10 Drops Per ML (gtts/ml) 500
---------------------------------------------------- = --------- = 25 gtts/min
20 minutes 20
** If the time is less than one hour then we just divide by the minutes ordered. In this case
20 minutes.**
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