Calculations, how to make them simple?

P_RN, ADN, RN · Aug 27, 2005

How about posting a hypothetical problem here.

For example you want to give 12 mg of phenergan and you have 50 mg/ml ampules. You also want to add 40 mg of demerol and you have 50mg/ml tubexes. How much of each and what will the total volume?

I don't have any cheat sheets. Equivalences are something to just learn.

On the heavy duty stuff like Dopamine drips I use the printed formula and have an independent person or two check behind me.

Just face it you are going to be a nurse so you will have to be fluent in metric.

milenko · Aug 27, 2005

Okay here goes, keep in mind I am looking for a way to simplify this, we have just started calculations in my class but our teacher (god bless her cotton socks) as much as I love her, the way she explains and my way of learning are two different things LOL Anywho here goes......

Patient is ordered a premedication of of Pethidine 25mg and Metoclopramide 10mgs. Stock strength of Pethidine is 50mg in 1 mL and 100mgs in 2mL. Stock strenght of Metoclopramide is 10mgs in 2mL.

What volume of pethidine is required to give 25 mgs?

What is the total volume when the two are mixed?

Thanks

How about posting a hypothetical problem here.
For example you want to give 12 mg of phenergan and you have 50 mg/ml ampules. You also want to add 40 mg of demerol and you have 50mg/ml tubexes. How much of each and what will the total volume?
I don't have any cheat sheets. Equivalences are something to just learn.
On the heavy duty stuff like Dopamine drips I use the printed formula and have an independent person or two check behind me.
Just face it you are going to be a nurse so you will have to be fluent in metric.

stidget99 · Aug 27, 2005

the formula that i use for most calculations follows. and as long as you have at least one half of the equation (gtts/min, mg/cc, mg/tab, etc.), then this formula will work.

order says to give 5mg of morhpine. it comes in 8mg/1ml ampule.

8mg : 1ml = 5mg : xml

! !_________! !

! !

!________________!

8x = 1 x 5

8x = 5

8 8

x = 0.625

notice placement of mg and ml. to initally set up your equation, make sure that same values are placed on the same side of the equation. for example, if mg is on left side of the first equation it's on the 1st side of the 2nd equation. same for the ml, on the right side of each equation. 'x' is the value that you are looking for.

once the equation is set up in this way.......you can go ahead and multiply things out. see the color coding. you don't need to worry about values until the end.

multiply the ends and the center as shown. again, notice the color coding.

the next step is to get the 'x' all on it's own by dividing (8x divided by 8 and 5 divided by 8).

or you can cross multiply...

8x times 8 64x 64 divided by 40

8 times 5 40

either way your answer is 0.625.

now go back and look at what value was next to the 'x' in the inital equation and that is the value that you want to put behind your answer........ml.

so your final answer is...........give 0.625ml. it's important that you go back and double check to make sure that your answer makes sense. for example, does it make sense that you are going to give 0.625ml? (i.e. 0.625 is over a little over half and 5mg is a little over half of the 8mg that it comes in- this makes sense).

knowing this basic equation will work for most (albeit not all) of the math that nurses need to know.

hope this helps. i had problems w/ the nursey math until someone showed this equation to me and have not had problems since nor have i had any calculation-based med errors.

milenko · Aug 27, 2005

i work night shift tonight, i have printed this off and will work on it and try and make sense of it, thank you vey much for taking the time to put it on here. ver much appreciated.

the formula that i use for most calculations follows. and as long as you have at least one half of the equation (gtts/min, mg/cc, mg/tab, etc.), then this formula will work.
order says to give 5mg of morhpine. it comes in 8mg/1ml ampule.
8mg : 1ml = 5mg : xml
! !_________! !
! !
!________________!
8x = 1 x 5
8x = 5
8x = 5
8 8
x = 0.625
notice placement of mg and ml. to initally set up your equation, make sure that same values are placed on the same side of the equation. for example, if mg is on left side of the first equation it's on the 1st side of the 2nd equation. same for the ml, on the right side of each equation. 'x' is the value that you are looking for.
once the equation is set up in this way.......you can go ahead and multiply things out. see the color coding. you don't need to worry about values until the end.
multiply the ends and the center as shown. again, notice the color coding.
the next step is to get the 'x' all on it's own by dividing (8x divided by 8 and 5 divided by 8).
or you can cross multiply...
8x times 8 64x 64 divided by 40
8 times 5 40
either way your answer is 0.625.
now go back and look at what value was next to the 'x' in the inital equation and that is the value that you want to put behind your answer........ml.
so your final answer is...........give 0.625ml. it's important that you go back and double check to make sure that your answer makes sense. for example, does it make sense that you are going to give 0.625ml? (i.e. 0.625 is over a little over half and 5mg is a little over half of the 8mg that it comes in- this makes sense).
knowing this basic equation will work for most (albeit not all) of the math that nurses need to know.
hope this helps. i had problems w/ the nursey math until someone showed this equation to me and have not had problems since nor have i had any calculation-based med errors.

BETSRN · Aug 27, 2005

Student nurse here, I am in the middle of practising my calculations and for the most part I can handle it, however I was wondering if maybe anyone out there has a cheat sheet that would have a quick way for conversions.
And help when figuring out volumes where two meds are required.
I know it will take practice, I just freeze when it comes to math, as I never liked it in school. Any help would be great and of course appreciated.
Thanks in advance.
Milenko

Just learn your process of equivalencces and stick with one way of doing the calculatons. It will become very easy. Calculate out every dose: even if it is the same dose you gave yesterday. Ther is a huge room for error when people do not check and double check. Even with regular unit dose meds you must always check the order before you give it. '

Even easy meds can be given incorrectly. Once, our pharmacy put a med time in our computer incorrectly and so the nurse gave way too much med because she gave it too soon. So, pharmacy was wrong as was the nurse for not looking it up. Personally, I never give a med (especially with our new computer system which is awful) unless I have looked at the original order and gone into the Pyxis to see when the last dose was actually given.