Help! Calculation question

Editorial Team / Admin · Feb 9, 2006

2 ml of Lasix 20 mg or 10 mg per ml.

bowkerj · Feb 10, 2006

Could someone please write out the steps -I'm not getting this

DaFreak71 · Feb 10, 2006

Hi, I am reviewing some calculation questions and this is the first time I've ever done this. I don't understand the following question... can someone please explain?
The NP prescribed 35mg of Lasix as a one-time dose for injection. The medication is available as 20mg in 2mL. The nurse will give:
Help!
What does it mean "20mg in 2mL"? 2mL of what? I'm confused!!!

Hi,

It means that each 2ml of liquid contains 20mg of lasix. If you're giving a shot, it can't be in tablet form so it has to be in a solution.

This is the way we have to work the problems in my program. It isn't the most intuitive way, but here goes:

Ordered: 35mg Lasix

Available: 20mg/2 ml

1st step: 20mg:2ml::35mg:xml

(this reads: 20 mg is to 2 ml, as 35 mg is to ?)

Multiply first and last together 20(x)

Multiply inner values: 2 (35)

20x=70

x=70 divided by 20

x=3.5ml

The way the problem is worded, it is saying that there are 20mg of lasix in 2ml.

Here's another example of how ratio and proportion work:

Ordered: 2 grams of xxx

Available 10mg/5cc

Step one: You have to convert the grams to milligrams.

State the known conversion:

1 g: 1000 mg::

Step two: on the right side you put what you are wanting know, with one piece of information. You MUST use the same format...if you start with g on the left side, you have to start with g on the right side.

1 g:1000mg::2 g:Xmg

1(x) = 1000 (2)

X=2000mg.

Now you have to figure out the rest of the problem....

Put what you know on the left side:

10mg:2 cc::

You have to insert the one piece of info you know on the right side now.

10mg: 2cc::2000mg: Xcc

10 (x) = 2 (2000)

10x=4000

x=4000 divided by 10

x=400 cc's.

Hope this helps!

Adri

bowkerj · Feb 10, 2006

Hi,
It means that each 2ml of liquid contains 20mg of lasix. If you're giving a shot, it can't be in tablet form so it has to be in a solution.
This is the way we have to work the problems in my program. It isn't the most intuitive way, but here goes:
Ordered: 35mg Lasix
Available: 20mg/2 ml
1st step: 20mg:2ml::35mg:xml
(this reads: 20 mg is to 2 ml, as 35 mg is to ?)
Multiply first and last together 20(x)
Multiply inner values: 2 (35)
20x=70
x=70 divided by 20
x=3.5ml
The way the problem is worded, it is saying that there are 20mg of lasix in 2ml.
Here's another example of how ratio and proportion work:
Ordered: 2 grams of xxx
Available 10mg/5cc
Step one: You have to convert the grams to milligrams.
State the known conversion:
1 g: 1000 mg::
Step two: on the right side you put what you are wanting know, with one piece of information. You MUST use the same format...if you start with g on the left side, you have to start with g on the right side.
1 g:1000mg::2 g:Xmg
1(x) = 1000 (2)
X=2000mg.
Now you have to figure out the rest of the problem....
Put what you know on the left side:
10mg:2 cc::
You have to insert the one piece of info you know on the right side now.
10mg: 2cc::2000mg: Xcc
10 (x) = 2 (2000)
10x=4000
x=4000 divided by 10
x=400 cc's.
Hope this helps!
Adri

That helps a lot! But how did you get 2cc from 5cc available??

AuntieRN · Feb 10, 2006

this is how I learned to do it: It's called dimensional analysis

mL=35mg x 2mL

_____ ______ = 70

1 20 mg _____

20 =3.5mL

You know you are looking for mL in your answer. The mg cancel out each other and just leave mL. it is what the doctor ordered times what is on hand, then you divide to get how many mL you are looking for. Hope I explained it clearly. I have an awful time with math but this book I have is wonderful. Good luck

DaFreak71 · Feb 10, 2006

That helps a lot! But how did you get 2cc from 5cc available??

LOL, sorry about that! It should have been:

10mg: 5cc::2000mg: x cc

10 (x) = 5 (2000)

10x = 10000

x = 10000 divided by 10

x = 1000 cc

:imbar Adri ( it's late and I get really dumb when I'm tired)

DaFreak71 · Feb 10, 2006

this is how I learned to do it: It's called dimensional analysis
mL=35mg x 2mL
_____ ______ = 70
1 20 mg _____
20 =3.5mL
You know you are looking for mL in your answer. The mg cancel out each other and just leave mL. it is what the doctor ordered times what is on hand, then you divide to get how many mL you are looking for. Hope I explained it clearly. I have an awful time with math but this book I have is wonderful. Good luck

I wish our school would let us use this method.

Adri

Boston-RN, RN · Feb 10, 2006

The formula we learned in math was

D (drs order)

------------- X 1 (if tab or cap) or # of mL

H (what's on hand)

so in the example given it's

35

--- X 2 mL = 3.5 mL

20

tinaroo07 · Feb 10, 2006

The formula we learned in math was
D (drs order)
------------- X 1 (if tab or cap) or # of mL
H (what's on hand)
so in the example given it's
35
--- X 2 mL = 3.5 mL
20

This is how I do it and it is easier for me; the other posts with the ratios is how a lot of my fellow students do it and it is easier for them. Just go with what is easier (as long as it comes out the same!)

Daytonite, BSN, RN · Feb 10, 2006

first of all, "20mg in 2ml means 20mg of lasix in 2ml of solvent (probably sterile water or saline)".

the old "dose desired divided by the dose on hand" formula works very well to solve this problem. it goes like this:

35mg of lasix

(dose desired)

/

20mg of lasix

(dose on hand)

x

2ml

(what your lasix on hand comes in)

=

3.5 ml

(the amount of the lasix solution you will draw up into a syringe and give) note: the labels "mg of lasix" will cancel each other out since one is in the numerator and the other in the denominator. this leaves you with one label that didn't cancel out: ml, and that is applied to the final arithmatic answer.

make sure you understand how to get this solution because this is a very practical problem and as a nurse you will most likely end up having to do this very calculation or others very much like it daily at your rn job.

MMARN, BSN, RN · Feb 10, 2006

This is how I do it and it is easier for me; the other posts with the ratios is how a lot of my fellow students do it and it is easier for them. Just go with what is easier (as long as it comes out the same!)

Exactly. Do whatever is easiest for you. I have found that the basic formula (D/H X V) and Dimensional Analysis works great for me. Proportion really screws me up. I saw one of the posts on the other page and all I could think was HUH???? :chuckle Just do what is easier for you. Trust me, you'll get it. (I'm terrible at math, and I got it.)