Having problem with math

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hi, i am a first year rn student...i am an older lady and i have been out of school for a little while now lol...i have always had a problem with math. as far as basic math, no problem..i just get confused where and how to plug the numbers in at. and with word problems, i try to plug every number in whether it is relevant or not. can someone please help me with this nursing math problem. i have the answer due to the answer sheet, but i need to be shown step by step how to work this problem out. any help will be greatly appreciated. it may seem very easy to some people, but it just doesn't click with me...

the order is for 1000 ml of 5% dextrose in water to run at 250ml/hr. how many drops per minute should the iv infuse (60gtt/ml set)?

question is: do i set it up like this: 250ml/60minutes * 60gtt/ml? if so the 60 will cross each other out leaving 250 gtt/ml? i know this is totally wrong!! do you put the 1000 ml into the equation? i guess you can see now how very confused i am!

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250 ml to be infused in one hour x a 60 drop set = 15000 drops to be infused in one hour

15000 drops / 60 minutes in one hour = 250drops per minute

They often give you too much info. You don't need to know the type of med or the total volume to be infused to arrive at the answer they are asking for.

NOTICE: The 60gtt per ml set, there are 60 minutes in an hour, hmmmm......that was a really good number to use for an infusion set, not just some number pulled out of a hat. Think about it enough and you can come up with an even shorter way to solve this.

Good luck in nursing school. I start my last semester in 3 weeks!

Charlie

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Thank you so much! Here again I was trying to plug in the 1000ml (total volume). I think I am making this more harder than it actually is. Once again thank you so much. Good Luck with Nursing school!

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What about this problem:

The order is for streptomycin 500 mg q 6hrs. The drug label reads 5 g in 12.5 ml. How many milliliters should the client receive?

OK: so I know I have to change 5g to mg right? Which would be 500 mg.

Then I would write 500/500 *12.5? which would give me 12.5ml?????

Did I just totally screw that one up?

My answer sheet says the answer is 1.25 ml....I just don't get that answer

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hey there,

this is how i solve this problem:

mL=12.5 mL / 5g x 1g/1000mg x 500mg = 1.25 mL.

if you write this out,you will see that units cancel each other out and you will be left with mL,which is what you are looking for. you were right that you need to convert 5g to mg. hope this helps.

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Specializes in Cardiac, Rehab.
What about this problem:

The order is for streptomycin 500 mg q 6hrs. The drug label reads 5 g in 12.5 ml. How many milliliters should the client receive?

OK: so I know I have to change 5g to mg right? Which would be 500 mg.

Then I would write 500/500 *12.5? which would give me 12.5ml?????

Did I just totally screw that one up?

My answer sheet says the answer is 1.25 ml....I just don't get that answer

5g is 5000mg. Remember, milli means thousands.

Always start the equation off with what it is you are trying to solve for. In this case its ML.

ML = 12.5ML/5g * 1g/1000mg * 500mg/6hrs

If you look at how I wrote it, I started with what I wanted to solve for on top, in this case ML. Then I plugged in the known ratios (12.5ML/5g) then a conversion (1g/1000mg) and then finally the 500mg/6hrs. In this case, the 6hrs is really a distractor, it isnt asking you for how much over time, just the total amount. I also make sure that when I write it all down, I get rid of the units I don't want in my final answer. In this case, I cancel out the grams with miligrams, and then cancel out the mg and am left with ML/Hr. Since there is no per hour amount required, you can toss out the hours, but its good practice to leave it in so you know you accounted for all the parts of the equation. That is the dimensional analysis or "nurse math" way of doing it.

Not to confuse, but in my head, I would look at it and say my dose is 500mg, the amount is 5000mg in 12.5ML, so the amount is one tenth or 1.25ML. But this is nursing school and they want to see it done their way.

You may want to find somebody in class that is good with math and have them sit with you for an hour or two and go through these types of problems. Practice is the only way you will get past them. Good luck.

Bob

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fosters girl

On some problems you may need the total volume, it really depends on what they are asking you to solve for.

ns88 and Bob are spot on for solving your second problem. Here is how I would attack it, this is a little different than most people would solve but it works for me.

1g = 1000mg, so, 5g = 5000mg

from our label we have a ratio of 5000mg in 12.5ml

ok, so now that we have all of our info, here we go

5000mg 500mg

------- = --------

12.5ml X ml

notice that milligrams are on top on both sides. I could have put the mg on bottom of both sides, it really does not matter.

now for the best part

"multiply the diagional that does not contain the unknown then divide by the only number thats left"

500mg times 12.5ml = 6250

6250 / 5000 = 1.25ml

This is how I set up the ratio type problems. Different people set up problems in various ways and that is OK. I learned this method many years ago and have applied it for all sorts of things. Let me know if this dosent make sense and I will give you a better example.

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After posting this I see that my equation is hard to read.

5000mg,,,,,,,,,,,,,,,,,500mg

-------,,,,,,,, =,,,,,,,,, --------

12.5ml ,,,,,,,,,,,,,,,,,,,X ml

There we go, just ignore all of the commas.

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Specializes in Emergency Nursing.

Total amount to be infused * conversion factor of tubing (drops per ml)

_________________________________________________________

Time in minutes to infuse over

In the case of your problem you can use either 250ml over 60 minutes or 1000ml over 360 minutes the conversion factor is 60 drops per mL

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Thank you all so much for your time..I do agree, everybody has different ways of doing math. You have all been a great help to me!

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What about this problem:

The order is for streptomycin 500 mg q 6hrs. The drug label reads 5 g in 12.5 ml. How many milliliters should the client receive?

OK: so I know I have to change 5g to mg right? Which would be 500 mg.

Then I would write 500/500 *12.5? which would give me 12.5ml?????

My answer sheet says the answer is 1.25 ml....I just don't get that answer

My teacher gave the formula of (D/H)*Q where:

D= doctor ordered

H= med on Hand

Q= quantity available

another thing, watch your unit conversions. Grams to Miligrams is moving the decimal 3 places to the right (* by 1000).

Therefore: 5g=5000mg

D=500

H=5000

Q=12.5mL

(500/5000)*12.5=1.25mL of medication per dose

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here is a quick way i learned from three nurses who have a lot of years of experience:

desired/have times quanity.

so: 500/5000 * 12.5 = 1.25 ml

the 5000 is 5 g (1 g = 1000 mg).

with that desired over have times quanity is how i took my dosage calculation and got a 97%.. it seemed to be the easiest with me. you just gotta remember to convert the numbers to the same unit.

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