Dosage calculations

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Can anybody show me how to calculate gtts/min and ml/hr using dimensional analysis? I use this method for all my calculations but I cant get it to work with setting IV rates if anybody could help it would be greatly appreciated. I can figure the rates using another formula so its not a matter of not knowing how to do them I just prefer help with Dimensional method only!

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Specializes in Hospice & Palliative Care, Oncology, M/S.

Are you asking how to convert gtts/min TO ml/hr? :)

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no its a formula you use to convert any dosage problem for example. The Doctor odered 4mg of a specific med and the dose you have on hand is 2mg tabs how many tabs so you give. you set the problem up to where what ever you have are trying to get goes on top and the drug amout goes on bottow then you muliple and divide. You know when the problem is set up properly because if you have mg on the bottom then the next fraction you write should have mg on the top of the next. I can solve any problem like this except gtt/min and ml/hr... when i took the class severle years back they showed us but I cant find my notes :( sorry if its a lil confussing I typed you a sample of a easy one.

tabs= tab/2mg x 4mg/x = 2tabs

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Specializes in EMT-P.

Without knowing your exact problem, I will make one up for setting up using dimensional analysis (Dimensional analysis is cool method I think).

Q. Compute flow rate for 1200ml of solution to be infused over 6 hr. gtt = 15gtt/ml.

Setup:

1200ml/6hr x 1hr/60min x 15gtt/1ml = (flow rate) = 50gtt/min

Since the units ml cancel, and units hr cancel we are left with unit gtt and minutes so we know we set up our problem correctly.

Does that help? If you have a specific problem you need help with, post it here and we will see if we can work through it using DA. :)

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Without knowing your exact problem, I will make one up for setting up using dimensional analysis (Dimensional analysis is cool method I think).

Q. Compute flow rate for 1200ml of solution to be infused over 6 hr. gtt = 15gtt/ml.

Setup:

1200ml/6hr x 1hr/60min x 15gtt/1ml = (flow rate) = 50gtt/min

Since the units ml cancel, and units hr cancel we are left with unit gtt and minutes so we know we set up our problem correctly.

Does that help? If you have a specific problem you need help with, post it here and we will see if we can work through it using DA. :)

I love DA... but where I keep getting confussed is your minutes does not cross out with minutes it crosses out with gtt's? I learnered it had if you had min on your bottom fraction you needed minutes on the top of your next fraction. Does this change if your doing gtt/min problems?

Im sorry if its confussing to read its hard to type math problems. But no I dont have a specific problem I need help with I just wanted to use DA for setting my IV rates since I use it calculate tabs caps mls ect with this method... Its just driving me crazy they dont cross out!!

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Your minutes shouldn't be canceling out because you're solving for drops per minute. If you're using a pump you're solving for ml per hour.

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i love da... but where i keep getting confussed is your minutes does not cross out with minutes it crosses out with gtt's? i learnered it had if you had min on your bottom fraction you needed minutes on the top of your next fraction. does this change if your doing gtt/min problems?

im sorry if its confussing to read its hard to type math problems. but no i dont have a specific problem i need help with i just wanted to use da for setting my iv rates since i use it calculate tabs caps mls ect with this method... its just driving me crazy they dont cross out!!

in that equation...

1200ml 1hr 15gtt

______x______x________

6hr 60min 1ml

the ml cross out.. the hrs cross out.. so your answer will be in gtt/min because that is what your looking to solve from the question, so when doing da you can double check to make sure your solving for what you need to be solving for. in other words, the min and gtt shouldn't cancel each other out.

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Specializes in PCU, Post surgical, Telemetry.

Here's how I was taught...

With that same question:

Q: Compute flow rate for 1200ml of solution to be infused over 6 hr. gtt = 15gtt/ml.

You start with what you are looking for which in this case is how many drops per minute.

gtt =

---

min

In this case where you begin with the fraction you carry gtts straight across and look for the info that pertains to gtts in the question. So:

gtt --> 15 gtts

--- = -------

min 1 mL

Then, as my teachers say "What's downstairs, goes upstairs", so you bring the bottom mL to the top of the next line.

gtt = 15 gtts 1200 mL

--- ------- x --------

min 1 mL 6 hr

Now, you probably know that you need to convert this part, bring the hr to the top of the next line and convert.

gtt = 15 gtts 1200 mL 1 hr

--- ------- x -------- x -----

min 1 mL 6 hr 60 min

Now that you've used all the information in the problem, you cancel out the mL, and hr (I just erased them to show that they're "cancelled"), and are just left with gtts/min, now you can solve.

gtt = 15 gtts 1200 1 18000 gtts

--- ------- x -------- x ----- = ------ = 50 -----

min 1 6 60 min 360 min

Hope that helps! :)

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Specializes in PCU, Post surgical, Telemetry.

Well, for some reason it's not lining up, but if you write it out hopefully it will make sense. :)

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Specializes in Emergency Dept. Trauma. Pediatrics.
Well, for some reason it's not lining up, but if you write it out hopefully it will make sense. :)

This is why I can never answer these questions on here, I am more like, grab a pencil and a piece of paper and I will show you and explain to you. To try and do math problems on here and have it all look right is hard. lol

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Specializes in EMT-P.

Maybe this will make things more clear. Lets see if this works :)

ivcalc.gif

We start with what we are given and should end with what we want. In this case we are given 1200ml over 6hrs and we want drops per minute or gtt/min.

So we start with 1200ml/6hr now we know we can't use hours and must convert hours to minutes thus we use

60 minutes in 1 hour or 1hr/60 min. Notice our Hr units cancel. Our other given was 15 gtt/1ml so we write that down thinking we need to get rid of the unit ml. Notice how it is written above this happens and only remaining units are gtt and minutes and hence the final answer. :yeah:

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I have a different way of attacking this kind of problem. I start doing them like this in paramedic school because I could not wrap my mind around the formula method. I like to keep it simple so that I can understand each thing step by step. I will use Carlie's numbers.

first step- 1200mL x 15gtt/mL = 18000 total drops to infuse

second step- 6 hours x 60 min/hr = 360 minutes

third step- 18000 drops divided by 360 minutes = 50 gtt/min

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