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I hated nursing school math exams.  I’m not the best at math, at all.  I’ve never taken a calculus or physics class in my entire life.  However, like many nursing schools, mine had a med math exam in every single course.  You had to get a 90% or above or you failed the entire class, no matter what the rest of your grade was.  And if that happened, you had to wait until the next year to retake the class.

No pressure.

In the real world, I use a few types of math but nothing like those darn tests.  I’ll calculate pump rates for IVPB meds and doses for partial dose meds.  That’s about it.  We always double (and triple) check our math with a few other nurses prior to administration.  Also, the computer typically calculates it as well.  However, if you work with babies or in peds, you’ll be giving everything based on weight.  So that means more math!

IV rates

Most IVPB meds come up from pharmacy with a rate already on it.  If not, your order should indicate it.  I honestly rarely need to use that anymore, if it makes you feel any better, since it’s always ordered and written somewhere.

Here is how you can figure out a rate if it’s not already on your order or med:

Let’s say you need to give 500 mg IV Keppra, which comes in a 100 ml bag.  You need to give it over 15 minutes.  What rate do you program?

Remember that rates are typically in milliliters per hour.  I picture a clock and how many times 15 will go into an hour, and times my amount

(100 ml) by that.

So, 15 minutes goes into an hour 4 times.

Therefore, 100 ml x 4 = 400 ml/hr

If you need to give something over a few hours, you just divide your amount by the amount of hours.

Let’s say you need to give 500 ml IVPB Vancomycin over two hours.

500 / 2 hrs = 250 ml/hr

I want 500 mls to go in over two hours, so just divide by two and it’ll go in at 250/hr!  If it’s going in over more than an hour, your rate will be less than your amount.

Partial dosing

Ok now let’s say you need to give a partial dose of an IV medication.  The easiest way to remember this is dose ordered divided by dose available times amount.  I remember it as DO-DA.  Take that dose your doctor ordered, divide it by the mg’s it comes in, and times it by the ml’s of the vial.

Example:  I want to give my patient 4 mg IV Morphine.  So I go over to my Pyxsis and pull out the Morphine that’s ordered.  My order says 4 mg, but the syringe that I pull is 10 mg/1 ml.  You’ll have to give a partial dose and waste the rest with another nurse.

4 mg (dose ordered) / 10 mg (dose available) X 1 ml (amount) = 0.4 ml

Alright, now let’s say you need to give your patient their dose of IV Solu-Medrol.  It’s ordered as 50 mg IV push.  Your vial says 125 mg/2 ml.  How many ml’s do you give?

50 mg (dose ordered) / 125 mg (dose available) X 2 ml (amount) = 0.8 ml

Make sense?  Just remember DO-DA!

A few things I use all the time

Memorize these!

  • 2.2 lbs = 1 kg
  • 1 oz = 30 ml
  • 1 inch = 2.54 cm

Side note: I never failed a math test and never failed a nursing course.  If I can do it, you can too.  Just study EXACTLY what they tell you to study.  Swish!

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