Med Math Examples

nurseprnRN, BSN, RN · Sep 17, 2012

I like the concept. Good luck on the execution-- not yours, that's fine, but the rest of the input you're bound to get (and have already anticipated). :woot:

Music in My Heart · Sep 17, 2012

Here's another one:

The patient is on a dopamine drip. The physician orders the dopamine increased to 25 mcg/kg/min. The patient weighs 177 kg. The dopamine is supplied in a concentration of 3.2 mg/mL in a 250 mL bag.

At what rate, in mL/hr, will you set your pump?

You are preparing the patient for a long ground transport. You check the pump and see that 177 mL have infused so far. The physician asks you how long the bag will last (assuming that the rate doesn’t change).

You tell the doc, “0.88 hours, ma’am.” With a slight chuckle she asks you if that will get the patient through the 50 minute transport. Will it?

Better make sure there’s another bag on the ambulance…

Music in My Heart · Sep 17, 2012

GrnTea said:
I like the concept. Good luck on the execution-- not yours, that's fine, but the rest of the input you're bound to get (and have already anticipated).

We'll see how it goes. If it proves to be no fun for me then I'll just stop. Got lots of other demands on my time, anyway.

I'd "LIKE" your post but not button is there to be seen ?

Music in My Heart · Sep 18, 2012

A client weight 187 lbs is receiving aminophylline 0.4 g in 500 mL of 0.9% saline solution at a rate of 80 mL/hr. You know that a therapeutic level for this drug is 0.4mg/kg/hr. Calculate the client's current infusion rate and determine how much drug per hour the client is receiving. Is this dosage subtherapeutic, therapeutic, or toxic?

nurseprnRN, BSN, RN · Sep 18, 2012

I like the different color cross-outs-- this will probably help people see what they should be thinking about.

Music in My Heart · Sep 19, 2012

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brillohead, ADN, RN · Sep 19, 2012

If it's okay to jump on board here, I'd like to offer this advice:

Don't let yourself make it too complicated!!!! You're just multiplying by one!!!!!

Music in My Heart · Sep 19, 2012

brillohead said:
If it's okay to jump on board here, I'd like to offer this advice:
Don't let yourself make it too complicated!!!! You're just multiplying by one!!!!!

Agreed... some people have difficulty, however, with the idea that numbers and units are algebraically equivalent, hence the decision not to skip any steps at all.

My personal approach is to do a quick-solve in my head and then work it out in full detail to ensure that I get the same answer... internal consistency increases the likelihood of accuracy.

madel0119 · Sep 19, 2012

i do having difficulty in simplifying med calculations,thanks for sharing not to be more complicated.Big help!!!more example please!

brillohead, ADN, RN · Sep 19, 2012

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Agreed... some people have difficulty however, with the idea that numbers and units are algebraically equivalent, hence the decision not to skip any steps at all.

I've found that a lot of my cohort were never taught that whole concept of "multiplying by one" -- they would try to "memorize the formulas" for each type of calculation, without ever having anyone explain *why* the formulas are set up the way they are in the first place. Once I teach them the concept of "equal to one", then all of a sudden they realize that they never had to memorize ANY big fancy formulas at all -- just multiply by one over and over until you get to the answer you need (yes, that's an overly-simplified way of looking at it, but often times they just need to RELAX, take a breath, and realize that it really is NOT as complicated as they are trying to make it!).

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My personal approach is to do a quick-solve in my head and then work it out in full detail to ensure that I get the same answer... internal consistency increases the likelihood of accuracy.

I always tell people to "do a sniff test" after finishing the formula. If you're putting in hundreds of drips per minute -- something's probably wrong. If you're infusing over a liter an hour -- something's probably wrong. If you're only doing 1-2 drips per minute -- something's probably wrong. If you're injecting less than 0.1mL -- something's probably wrong. If you have to use more than one vial of something to draw up what you need (or if you need more than one 10mL syringe), something's probably wrong.

Also, they should run the formula backwards once they find their answer, to make sure the math works in both directions. Number of drips per minute times number of minutes to find total volume infused. If it doesn't work out to the original amount, then you missed something somewhere!

Music in My Heart · Sep 19, 2012

Yes.. the "sniff test!!"

In engineering analysis classes we were always instructed to check for the "reasonableness" of the answer. I think a lot of people would do well to spend time with a stopwatch, an eye dropper, measuring spoons, a small measuring glass, a large measuring cup, and a kitchen scale... trying to get a sense of "reasonableness."

You're also right about the "freaking factor"... that is, people becoming flustered and confused because they do not understand the simple underlying concepts... the internal distraction is a killer.