Dosage Calculation HELP!

Samm06, BSN, RN · Jul 21, 2015

The chart in your book is giving you approximate conversions of liters to ounces. 1L is actually 33.8140227 oz but that is too hard for most student nurses to remember.
If the desired answer to the question is in ml then the measurements should be in ml.

Thank you. I was able to do some more practice problems after posting the original questions, and with everyone stating 1L=1,000 mL it has helped me answer other questions correctly.

Mavrick, BSN, RN · Jul 21, 2015

Thank you. I was able to do some more practice problems after posting the original questions, and with everyone stating 1L=1,000 mL it has helped me answer other questions correctly.

You are now an official convertee to metric.

Using metric measurements makes for much easier calulations.

KelRN215, BSN, RN · Jul 21, 2015

Rudimentary knowledge of the metric system is needed in nursing. 1L = 1,000 mL. That's the very definition of 1 liter. It's also 100 centiliters, 10 deciliters, etc. Milli = 1/1000 of the base unit, centi = 1/100, deci = 1/10. In the case of volume, liter is the base unit. I really cannot think of a situation in nursing where you'd be given units in metric and need to convert to US units. Actually, I can think of one. When you weigh a child in kg and the parents want to know their weight in lbs/oz. That's it.

1 liter is not equal to 1 quart. They are close but not equal and you had no need to go doing any conversions involving pints and quarts at all. 1L = 1000 mL, that's all you need to know to do this math. Multiplying 1000 x 0.75 and 0.25 can be done in one's head.

missmollie, ADN, BSN, RN · Jul 22, 2015

Just work on the metric system, which eventually becomes really simple once you work with it enough. Here's a worksheet that will force you to work "forwards" and "backwards" with the metric system. It's a great place to start:

http://www.sciencespot.net/Media/metriccnvsn2.pdf

From there, check out this amazing website, aimed at helping nurses with med calculations. They have unit conversion link you should check out. Work on these until you can do any question they throw at you! You can even sign up and have them send you a med calc question every day to your inbox, so you can keep your skills fresh:

DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

Best of luck!

SopranoKris, MSN, RN, NP · Jul 22, 2015

Question: Explain how you would prepare each of the following hydrogen peroxide (solute) and normal saline (solvent) irrigation orders:
1L of 1/4 strength solution
1L= 1q = 32 fl oz = 2pt = 960 mL (is this correct?)
The question is asking for an answer in mL.
The book's answer is:
250 mL hydrogen peroxide (solute) + 750 mL normal saline (solvent) = 1,000 mL (1L) of the 1/4 strength solution.
How does 1,000 mL = 1L when I calculated 32 fl oz x 30 mL = 960 mL?
for my answers I got: 240 mL solute (hydrogen peroxide) and 720 mL solvent (normal saline) = 960 mL total solution = 1L right?
I'm really confused with these calculations.

It's asking for 1/4 strength solution. Think about it. If you have 4 quarters in a dollar (100 cents), 1/4 is 25 cents. If you had 1 L (which is 1,000 mL), 1/4 of that is 250 mL.

Did that make it a bit clearer? The trick to med math questions is figuring out what they're actually asking. 1/4 of a liter is 250 mL. So, you'd have 250 mL of H2O2 and 750 mL H2O :up:

Samm06, BSN, RN · Jul 23, 2015

It's asking for 1/4 strength solution. Think about it. If you have 4 quarters in a dollar (100 cents), 1/4 is 25 cents. If you had 1 L (which is 1,000 mL), 1/4 of that is 250 mL.
Did that make it a bit clearer? The trick to med math questions is figuring out what they're actually asking. 1/4 of a liter is 250 mL. So, you'd have 250 mL of H2O2 and 750 mL H2O

HMMM wow, can't believe i didn't think of it that way :/ THANK YOU!

Plutonium261 · Jul 23, 2015

It's asking for 1/4 strength solution. Think about it. If you have 4 quarters in a dollar (100 cents), 1/4 is 25 cents. If you had 1 L (which is 1,000 mL), 1/4 of that is 250 mL.
Did that make it a bit clearer? The trick to med math questions is figuring out what they're actually asking. 1/4 of a liter is 250 mL. So, you'd have 250 mL of H2O2 and 750 mL H2O

THIS! The entire time I was literally thinking, and about to write, this exact thing. OP, you were saying that the quart thing wasn't confusing you, but it was the exact thing confusing you. All you needed to do was stop thinking of it in the conversion factors of your book, and think of it in terms of them asking you for 1/4, 0.25, of the 1L. 1L = 1,000 mL. 1/4, 0.25, or a quarter of 1,000 mL is 250 mL. As you now see, it really is that simple. Good luck to you my friend, you are well on your way to being great at med math!

Samm06, BSN, RN · Jul 23, 2015

So when the strength amount is provided, I'm first finding the solute correct? and that would be the part of the question (like for example to 1/4 strength)? and just subtract the solute from the total to get the solvent, and these together equal the solution, correct? i just want to be able to remember the steps in my head.

203bravo, MSN, APRN · Jul 23, 2015

So when the strength amount is provided, I'm first finding the solute correct? and that would be the part of the question (like for example to 1/4 strength)? and just subtract the solute from the total to get the solvent, and these together equal the solution, correct? i just want to be able to remember the steps in my head.

Just attempt to do it in different quantities --- if you have a 500 mL bag of normal saline and 1L of H2O2 -- how could you make the normal saline a 1/4 solution? what about a 250mL bag of normal saline?

Take the total amount of the saline and divide by 4 -- this tells you how much of the saline needs to be removed from the bag and how much H2O2 would have to be added to reach the required strength.

What if you wanted a 1/3 strength solution for a 1L bag of normal saline? 500mL NS? 250mL NS?