Alligations: A Question about 1/3 Normal Saline Solution and Sterile Water for Injection

by Sherri
(Raleigh, NC)


A liter of 1/3 NS is to be prepared from 23.4% concentrated sodium chloride solution and sterile water for injection. How many milliliters of each are to be used?What is 1/3? Can you walk me through this?The book says the answers are 333 mL of NaCl and 667mL of water. I can't figure out how they get this answer or how to get it. Can you please post my problem on your website? If you can't answer my question, maybe one of your visitors can.

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starstarstarstarstar 		A Question about 1/3 Normal Saline Solution and Sterile Water for Injection
by: Anonymous

tic tac toe looks like this : upper left is 0.9 ( NS) lower left is 0 (water) in the middle 0.3 (strength of the solution to be prepared i.e 1/3 x.9 =0.3) upper right is 0.3 (difference between the desired % and lower % i.e :0.3-0=0.3). lower right is 0.6 ( difference between higher % and desired % i.e :0.9-0.3=0.6)

total parts = 0.3+ 0.6 = 0.9

Amount of NS= 0.3/0.9 x1000 = 333.33 mL

Amount of water = 0.6/0.9 x 1000

Hope this helps!!
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starstarstarstarstar 		Same problem
by: Anonymous

I am deriving the same answers you are.
Very strange.
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starstarstarstarstar 		Here’s your answer
by: Anonymous

I had this exact problem in my book and the answers are 13ml of saline and 987ml of sterile water.

Middle square is 0.3% which is 1/3 of NS. My book says my answer is correct, so I’d definitely say your book has an error and that’s why you couldn’t get your answer to match.
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starstarstarstarstar 		Here is the REAL answer to your question.
by: Anonymous

Okay Pharma techs...here it is

1/3 NS is 1/3 of NORMAL Saline. Normal saline is
0.9%. In order to do the problem you must find out how much 1/3 of normal saline is. So...
1/3 x 0.9 = 0.3%

0.9 is your high
0.3 is what you want
0 is the low because there is no saline in your diluent.

0.9 0.3
0.3
0 0.6
Total 0.9

0.3 x 1000mL 0.6 x 1000mL
--- = 333.3 --- =666.7
0.9 0.9

I hope this helps all the other people like me who struggled with this problem.
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starstarstarstarstar 		how do I set up tictactoe table (desired/on hand)
by: Anonymous

thanks for helping but you didn't tell me how to set up tic tac toe table (desired/on hand) using the 1/3 to obtain the 333 and 667?How do I set up ratio/proportion table ? I understand your reply to a certain extent but it was still sort of vague.Where do you get 1/2 from 1/3?I know you can use only distilled and sterile water.From what i've heard you calculate the water as 0%, I was trying to put .33 as 1/3 in tic tac toe table.Is there another percentage I should use/can use for 1/3?I apologize if this seems like a stupid question
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starstarstarstarstar 		Answer about 1/3 Normal Saline Solution and Sterile Water for Injection Question
by: Anonymous

I’m more than happy to help you answer your question on IV compounding. As a pharmacy tech, this is going to be an important formula for you to understand. So, we’ll work through this question together.

The first thing to understand is that NS stands for Normal Saline. This liquid will typically contain .9% mass volume. When delivering this solution intravenously, of the 1,000 mL that goes into the patient, about 250 mL will remain in their system during the course of an hour treatment.

Now, 1/3 NS means that the IV compounding is 1/3 normal saline. The problem is that based on how the question is supposed to be resolved, you will never end up with 333 mL of NaCl and 667mL of water. Those results would come from a 1/2 normal saline solution. This is the saline at .45% which is where the treatment fluid needs to be, in an effort to ensure proper therapy.

When a patient is given 1000 mL of a solution that is .45% NS, it will be the equivalent of providing them 500 mL of NS and 500 mL of standard water. This combination can then successfully help to treat a patient that has suffered from dehydration. The result would be 333 mL of NaCl in the intracellular fluid, while delivering a total of 667 mL of water fluid. The end being the full 1000 mL of solution, knowing the starting formulas is important in this case.

It will be important to look at the 23.4% concentrated sodium chloride solution. This is the common formulation of sodium chloride solution that you will find. For any concentrated solutions of sodium chloride you do need to ensure you are properly breaking them down based on their ratios.

If you proceed to make the normal saline for any reason, it is important to understand that tap water won’t be a good choice. The standard formula for saline has the water listed as purified water.

Hopefully, this answers your question about IV compounding. Good luck in your pharmacy tech program. This will be an exciting and informative role for you to fill.
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starstarstarstarstar 		Can someone answer/reply to this question already?
by: Anonymous

How is someone supposed to figure out how to set up the tic tac toe table or figure out how to solve this if nobody answers this question or replies to it?What is the point in anyone contributing math questions in first place if no one ever replies to their posts?It defeats the purpose of posting questions to begin with.This is very annoying.

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