IV math help

  1. Hey everybody,

    Im hung up on a couple IV problems:

    Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
    answer is 18.75 ml/hr

    How do they get that?

    Also

    Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min

    I have the answers but dont know how they got em.

    Thanks !
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  2. 5 Comments

  3. by   smk1
    Quote from FNPhopeful
    Hey everybody,

    Im hung up on a couple IV problems:

    Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
    answer is 18.75 ml/hr

    How do they get that?

    Also

    Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min

    I have the answers but dont know how they got em.

    Thanks !
    1. 40/3= 13.3 hours then 250/13.3= 18.79 ml/hr

    2. 75/60= 1.25 then 1.25 x 20= 25 gtt/min
  4. by   Finallyat40
    Okay here goes...hope this helps:

    I always use the "what you have and what you need" theory:

    Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
    answer is 18.75 ml/hr

    So you have Morphine 40 mg/250ml = 250 divided by 40 = 6.25ml/1mg
    What you need: How many ml = 3 mg/hr = 6.25 X 3 = 18.75 ml/hour

    Does that make sense?

    Okay #2

    Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min

    75 ml/hr X 20 gtt/ml = 1500 gtt/ml divided by 60 minutes = 25 gtt/min

    Hope this helps...it's hard to write it down so that it makes sense.

    Jamie
  5. by   Daytonite
    morphine sulfate 40mg in 250 ml to infuse at 3 mg/hr. how many cc's per hour will the infusion run?
    by dimensional analysis, or factor label method, you want to end up with the labels of ml's/hour (because that is how you have given the answer). here's how you set this problem up:
    3 mg/1 hour (dose desired) x 250 ml/40 mg (amount you have on hand) = 18.75 ml/hour
    you set this equation up in order to manipulate and end up with the labels you want on the final answer.
    1000cc 0.45% ns at 75 ml/hr. administration set: 20 gtt/ml. how should you regulate the iv?
    again, by dimensional analysis, or factor label method, you want to end up with the labels of gtts/minute. here's how you set this problem up:
    75 ml/1 hour (rate desired) x 20 gtts/1 ml (drip factor) x 1 hour/60 minute (conversion factor) = 25 gtts/minute
  6. by   SchoolRN,BSN
    hi,

    i don't know how your school is teaching you to do math problems, but ours is using dimensional analysis. supposedly, it works with every problem if you use it the same way every time. i don't have enough experience to know if that's true, but i was able to figure out your questions using it, so maybe they are right!

    here is how i did it:

    1. always use the formula need = order x available

    2. in the first problem, you need ml/hr.
    ml
    ---- =
    hr

    3. your order is 40 mg in 250 ml. because you know you want ml on top, reverse the numbers & make it 250ml/40 mg.
    ml 250 ml
    --- = ----------- x
    hr 40 mg

    4. finally, you have available, the ability to use 3mg in one hour.


    ml 250 ml 3mg
    --- = ------- x ------ =
    hr 40 mg one hour

    5. you know your math will work because you can cross out the mg & you have ml/hour left for your answer.
    a. 250 x 3 = 750
    b. 40 x 1 = 40
    c. 750 divided by 40 equals 18.75 ml per hour

    the other problem works the same way.

    need = gtts/min
    order = 75 ml/hr
    avail - 20 gtts / ml
    * with this one you have to use a conversion factor to get your hour into minutes. set it up like this:

    gtts 75 ml 20 gtts 1 hour
    ---- = ------ x --------- x --------
    min 1hr 1ml 60 min

    75 x 20 x 1 = 1500
    = ------------------ = 1500/60 = 25gtts/min
    1 x 1 x 60 = 60




    it has helped me to do every problem the same. hope this works for you also.

    good luck
    Last edit by SchoolRN,BSN on Dec 3, '06 : Reason: Oops, didn't mean to duplicate Daytonite. I had to take my daughter's bf home before I finished...didn't see her reply.
  7. by   Icess64
    I didn't even post the question, but I'm thankful that you guys answered it so well! I do fine with dimensional analysis when it comes to everything except IV problems...they trip me up every time, and I have to pass the test on Tuesday! This helps very much!

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