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Medical Math - Calculating Fluid Additives

Views: 33028 - Comments: 25

Megan Brashear, CVT, VTS (ECC), demonstrates how to calculate the amount of drug to add to a full and partially full bag of IV fluids.

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Megan Brashear's picture
Megan Brashear


Enrolled: 07/2011

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Jessica Perkins's picture

Can you make a video on how to calculate a CRI if know mg/kg/hr and the rate, and want to find out how many mg/L to add?

Sarah Crisp's picture

Hey Jessica, we definitely can! We'll get that up for you ASAP.

kiyomi davis's picture

Hey Megan just curious what bag you were talking about in this video. At our hospital we no longer carry norm-r we've switched to p-lyte so I'm just wondering because I don't know if the quantity of kcl is the same.

kiyomi davis's picture

Forgot to ask but, does it even matter if we're using different bags?

Megan Brashear's picture

Hi Kiyomi, the type of fluids doesn't matter, you only care about the volume you are dealing with. Your doctor will give you a dose of KCl to add (like 20mEq/L, or 15mEq/L etc) and you will do the same math for P-lyte or Norm or NaCl. Think of it like giving a dose of antibiotics to a labrador vs. a husky. You only care how much they weigh, not their breed. Same with IV fluids and additives.

Jennifer Whitten's picture

Hi Meagan, I am a relatively new RVT and am moving into a full-time ER tech position. When it comes to adding for example potassium to fluids I was under the impression we have to account for the 4 mEq that is already in the LRS bag or does the doctor already take that into consideration when giving us the dose? Or does it just depend on the practice? Thanks!

Megan Brashear's picture

Hi Jennifer! Please be sure to check with your doctors/hospital to determine that. At DoveLewis, the amount ordered is what we add, if the doctors want it to be a TOTAL of 20mEq/L they will order 16mEq/L. As technicians we do not account for what is already in the bag. Good luck in your new job!

Evelyn o's picture

Awsome video! I was just thinking of this! We need more tech math please!!! Percentages% for example 50% to 5% dextrose or d5w

Heather Holbrook's picture

Who knew that medical math could be so stress-free?? Thank you for teaching fluid additive calculation in a way that is easy for this mathmatically-challenged individual to grasp the first time around!

emily barrett's picture

what about kcl changes ex: a bag has 5meq/L then when the bag has 750mls left the dr asks to increase it to 10meq/l

Megan Brashear's picture

Emily - to increase the amount in a bag that is partially full - you will add the difference. So a bag with 750ml remaining has 5mEq/L and you are asked to increase it to 10mEq/L. 10-5 means you need to add 5mEq/L. 5 x 0.75 = 3.75mEq needed for the 750ml. 3.75/2 (what you want divided by what you have) = 1.9ml. So you add 1.9ml of KCl to the 750ml of fliuds and your new concentration is 10mEq/L. Make sense?

Paula Millican's picture

Since the update this video will not play. It takes you to the please sign up page. Please advise.

Thank you,

Megan Brashear's picture

Thanks for the heads up! We have the video working again - thank you for your patience!

Jessica Ward's picture

Hey Megan,

Before the updates to your website there used to be PDF documents that went along with the videos....are those going to be coming back?!

Thank you

Megan Brashear's picture

Yes Jessica, those are coming back! With the updates we now have a new process for creating the add ons, but I will get the math worksheets moved to the top of the list! 

Maj-Lis Tuccolo's picture

Hello, if we are adding multiple medications to the same bag of fluids how does that change things? I'm looking at a question in the training kit test. Thanks!

Megan Brashear's picture

With multiple drug additives, you need to first ensure that all of the additives play nice with one another (like metoclopramide and KCl are commonly used and are fine to be in the same bag) and then double check the doses of all of the additives if the fluid rate changes.

Terri Massa's picture

I think it would be clearer if you erased the 'm' in 'mL' when you move the decimal point, to make it understood that you're converting from milliliters to liters. It's also not correct mathematically to move the decimal point without changing the units.

Chris Green's picture

Great catch Terri! You are correct that when moving the decimal point we should have dropped the m in mL, to make it L. Thanks for pointing that out!

Kelly Norden's picture

Hi there! Could you please post a video of how to increase a bag that has 10mEq KCl/L to 20mEq KCl/L that has 900mLs (or some other number less that 1000) left in the bag?

Holly Hayes's picture

Hi Kelly,

Thank you for reaching out! My name is Holly and I work with our accounts. I have added your suggestion to our content request list, and we will try to work on this as soon as possible.

Please feel free to reach out to me directly at with any further questions or thoughts.

Jennifer Howard's picture

Would love to see a video about reconstituting meds. Our hospital does ampicillin as 30mg/mL often and sometimes it seems to take me forever to get there!