Math help please!

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Specializes in ED/trauma.

i am terrible at iv dosage calculations! well at work we have to take a compentency test, so i asked my coworkers and found out that i was not alone. we don't have to do these much at my hospital, but i feel really stupid and want to gain more confidence. can anyone share any secrets or tell me what formula they like. also does anyone know of any good programs for handhelds? i mostly have problems only with certain kinds of calculations, i'll give you a few examples from the test.

1.you have an order for 10,000 units heparin in 500 ml ns iv to infuse at 750units/h on an infusion pump. what is the flow rate in ml/h? 38??

2.a 170lb. pt with minimal urine output has an order for dopamine @5mcg/kg/min. the premixed bag of dopamine contains 800 mg in 500 ml d5w. how many ml of solution dopamine will the pt recieve each hour? 14??

3. the order reads 40 grams of magnesium sulfate in 1000ml sterile water. what is the flow rate if you give 2 grams of magnesium sulfate per hour? 20??

i don't want to feel incompetent anymore. i don't even know if these are correct. and if they are i'm not even sure how i came to the answer. can anyone help?:crying2::bluecry1::banghead::confused:

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Specializes in L&D, PACU.

Ugh... Let me try this again

Tell you what. Grin. I posted an answer and then redid the calcs and I was off. So...How about you go to this thread which has great websites for math help....

https://allnurses.com/forums/f50/dimensional-analysis-math-problems-website-nursing-math-202109.html

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i am terrible at iv dosage calculations! well at work we have to take a compentency test, so i asked my coworkers and found out that i was not alone. we don't have to do these much at my hospital, but i feel really stupid and want to gain more confidence. can anyone share any secrets or tell me what formula they like. also does anyone know of any good programs for handhelds? i mostly have problems only with certain kinds of calculations, i'll give you a few examples from the test.

1.you have an order for 10,000 units heparin in 500 ml ns iv to infuse at 750units/h on an infusion pump. what is the flow rate in ml/h? 38??

2.a 170lb. pt with minimal urine output has an order for dopamine @5mcg/kg/min. the premixed bag of dopamine contains 800 mg in 500 ml d5w. how many ml of solution dopamine will the pt recieve each hour? 14??

3. the order reads 40 grams of magnesium sulfate in 1000ml sterile water. what is the flow rate if you give 2 grams of magnesium sulfate per hour? 20??

i don't want to feel incompetent anymore. i don't even know if these are correct. and if they are i'm not even sure how i came to the answer. can anyone help?:crying2::bluecry1::banghead::confused:

i came up with basically the same thing. i rounded up on #2 and got 15 ml/hr.

i came up with 50 ml/hr for #3.

i hope someone else will check on the answer for #3, i'd hate to challenge your answer if i'm wrong.

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i am terrible at iv dosage calculations! well at work we have to take a compentency test, so i asked my coworkers and found out that i was not alone. we don't have to do these much at my hospital, but i feel really stupid and want to gain more confidence. can anyone share any secrets or tell me what formula they like. also does anyone know of any good programs for handhelds? i mostly have problems only with certain kinds of calculations, i'll give you a few examples from the test.

1.you have an order for 10,000 units heparin in 500 ml ns iv to infuse at 750units/h on an infusion pump. what is the flow rate in ml/h? 38??

2.a 170lb. pt with minimal urine output has an order for dopamine @5mcg/kg/min. the premixed bag of dopamine contains 800 mg in 500 ml d5w. how many ml of solution dopamine will the pt recieve each hour? 14??

3. the order reads 40 grams of magnesium sulfate in 1000ml sterile water. what is the flow rate if you give 2 grams of magnesium sulfate per hour? 20??

i don't want to feel incompetent anymore. i don't even know if these are correct. and if they are i'm not even sure how i came to the answer. can anyone help?:crying2::bluecry1::banghead::confused:

you are well on your way with these calculations. adpie10, i too got 50 ml/hr for #3. here's my steps in calculating (i use dimensional analysis to see and cancel my units):

#1: 500 ml/10,000 units x 750 units/1 hr= 37.5 or 38 ml/hr

#2: 170 lb/2.2=77.27 kg

77.27 kg x 5 mcg/kg/min x 60 min/1 hr=23181 mcg/hr

23181 mcg/hr x 1 mg/1000mcg x 500 ml/800 mg= 14.48 or 14 ml/hr

#3: 40 g/1000ml=0.04 g/ml

2 g/hr x 1 ml/0.04 g=50 ml/hr

remember not to round too early in the steps or your answer will be off. if i have made a mistake in the math, i apologize. :cool:

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First, I would question the sterile water order? The easiest way I find is to make a simple fraction.

First: take what you have on hand. 40grams

--------

1000ml

Second: take what you need to give: 2grams

-------

X

The X will be the ML/hr; however, we do not know this value as of yet.

The final formula should look like this:

40grams 2 grams

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

1000ML X

Now, we simply sross multiply and solve for X.

40 times X= 40X and 1000 times 2 equals 2000.

So: 40X=2000. To solve for X we need to divide both sides by 40. Remember, basic algebra from school. What you do to one side of an equation, you need to do to the other.

After dividing each side by 40, you have X=50ml. So, 2 grams of mag in this concentration equals 50ml. Then, you simply set the rate at 50 ML/hr.

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Specializes in MICU.

easiest way that I taught myself...

Step 1 - Calculate your mL's per hour - So, if you are running 1 L over 8 hours, it's 125 mL/hr

Step 2 - Multiply your mL/hr by the drip rate - So, 125 mL/hr x 15 gtt = 1875

Step 3 - Divide the product of mL/hr X gtt rate by 60 minutes (just 60) - So, 1875 / 60 = 31.25 gtt/min

Hope that helps!

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Specializes in ED/trauma.

Thank you so much, some of these sites are really helpful, more helpful than my books!

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Specializes in Emergency/Trauma/Critical Care Nursing.

ok i got all the same answers as everyone but i use the ratio and proportion method, because im a very visual person and the fraction method screws me up, i can't do the math in my head lol , so i don't know if this will help but for example,

#3 i did like this...

if you have 40g=1000ml::2g=Xml

multiply outsides then insides : 40gX = 2,000g/ml

to get X by itself divide both sides by 40 : X = 50ml

Like i said, u might have already gotten the answers figured out, but i couuld NOT undestand that math no matter how i tried until someone showed me the ratio/proportion way and then it was like a lightbulb went on, im much more visual , i need to see each step to understand it i guess.... i hope this can maybe help u like it did for me!:idea:

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Specializes in ICU.

program the pump......ivpumps now a days have drug calc already set up, you just program the numbers you have (drug amount/solution amount/patient weight/dose wanted) and it figures out the rate giving you lots of options..mcg/kg/min, mcg/min, mg/hr etc.......:smokin:

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Specializes in Peds/Neo CCT,Flight, ER, Hem/Onc.
program the pump......ivpumps now a days have drug calc already set up, you just program the numbers you have (drug amount/solution amount/patient weight/dose wanted) and it figures out the rate giving you lots of options..mcg/kg/min, mcg/min, mg/hr etc.......:smokin:

Programmable pumps are great but should not be soley relied upon. There is a risk of human error when inputting the data. You should always double check the rate by doing the math yourself. A few days ago we transported an infant who had been receiving, at the referring hospital, Prostin at 10 times the dose she should have because of an error when programming the pump (even with the Pharmguard program!). The baby had to be intubated because of it. Please don't rely on the machines. Double check everything!

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Specializes in Adult ER, Medical ICU.
Programmable pumps are great but should not be soley relied upon. There is a risk of human error when inputting the data. You should always double check the rate by doing the math yourself. A few days ago we transported an infant who had been receiving, at the referring hospital, Prostin at 10 times the dose she should have because of an error when programming the pump (even with the Pharmguard program!). The baby had to be intubated because of it. Please don't rely on the machines. Double check everything!

FlyinScot, I agree with your response regarding the use of the pumps. Being able to calculate the dosages manually is a great way to double check that everything is OK. Guardrails/Pharmguard is a good tool to have but like any other machine, it relies on the soundness of the programming, and who is to say the machine's fotware will be 100% correct and free of bugs.

To OP:

That being said, I think the method of calculating what you have on hand using the factor label method (dimensional analysis) where you figure out what you have on hand and what you want at the end will help you arrive at the right destination with the correct units. It might be tedious, but it will help you with the thought process.

from a quick google search i found some links that might be helpful.

check out these sites for examples:

http://www-isu.indstate.edu/mary/tutorial.htm

http://www.geocities.com/HotSprings/8517/Quiz/quiz.htm

http://home.sc.rr.com/nurdosagecal/

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Specializes in ED staff.

I'll have to admit that I am terrible at math too.... I cheat, we always have a drug book with the mcg/kg/min listed in it, so all I do is set the pump at the rate stated. Luckily, I am fulltime triage, so I don't have to do it anymore. Like you I feel dumb, dumb, dumb and know that I should really try to remember how to do the math, but it's like anything else, if you don't use it, you lose it.

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