dosage problem...need help

  1. Sorry guys, but going through some examples our instructor gave us and am having some difficulty. I may have to post more later on.

    1) 0.9 gm of Cordarone in D5W has been prescribed for IV infusion at a rate of 0.5 mg per minute. The IV solution has a total volume of 500ml. The IV should be infused at how many ml per hour?

    2) An IV of D5W containing 2 mg of epinephrine and a total volume of 250 ml is to be infused at a rate of 15 mcg per minute. At how many ml per hour will you infuse the IV.

    3) An IV of D5W containing 2 mg of Isuprel and a total volume of 250ml is to be infused at a rate of 1 mcg per minute. At how many ml per hour will you infuse the IV

    I am sure I am just looking to far into this, but it is just not making any sense to me.
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  2. 17 Comments

  3. by   ♪♫ in my ♥
    Quote from mcknis
    sorry guys, but going through some examples our instructor gave us and am having some difficulty. i may have to post more later on.

    1) 0.9 gm of cordarone in d5w has been prescribed for iv infusion at a rate of 0.5 mg per minute. the iv solution has a total volume of 500ml. the iv should be infused at how many ml per hour?

    • you have 0.9 grams in 500 ml or 0.0018 grams in 1 ml or 1.8 mg in 1 ml
    • since 1 ml has 1.8 mg: 1 ml is to 1.8 mg as x is to 0.5 mg
    • 1 ml / 1.8 mg = x / 0.5 mg or x = (0.5 mg)(1 ml)/(1.8 mg) = 0.28 ml
    • that is, in 1 ml of solution there's 1.8 mg; in 0.28 ml there's 0.5 mg
    • so, if you want a rate of 0.5 mg per minute, you need to flow 0.28 ml per minute.
    • if you flow 0.28 ml in 1 minute then you flow 2.8 ml in 10 minutes, 5.6 ml in 20 min, and 16.8 ml in 60 minutes (16.8 ml/hr)

    2) an iv of d5w containing 2 mg of epinephrine and a total volume of 250 ml is to be infused at a rate of 15 mcg per minute. at how many ml per hour will you infuse the iv.

    3) an iv of d5w containing 2 mg of isuprel and a total volume of 250ml is to be infused at a rate of 1 mcg per minute. at how many ml per hour will you infuse the iv

    i am sure i am just looking to far into this, but it is just not making any sense to me.
    #2 and #3 follow the same process. give 'em a shot and post back to have your worked checked.
  4. by   Daytonite
    0.9 gm of cordarone in d5w has been prescribed for iv infusion at a rate of 0.5 mg per minute. the iv solution has a total volume of 500ml. the iv should be infused at how many ml per hour?
    you want to end up with an answer that has ml's/hour attached to the numbers. the information in the question includes minutes which means you are going to have to apply at least one conversion factor to change from minutes to hours. i also see that you have grams and mgs mixed into the problem as well so another conversion factor is going to be needed. actually, you want to clear the "grams" and "milligram" labels completely anyway because they aren't needed in the final answer. dimensional analysis (the factor label method) works very well for this. begin with the basic formula of dose desired divided by the dose on hand gives you the dose to give.
    terms you will need for this calculation
    dose desired: 0.5 mg/1 minute (given information)
    dose on hand: 500 ml/0.9 gram (given information)
    conversion factor: 60 minutes/1 hour (to convert minutes to hours)
    conversion factor: 1 gram/1000 mg (to convert grams to milligrams and vice versa)

    put each of these relationships (ratios, fractions) into a equation in a way (one label in a numerator and it's match in a denominator) that the unwanted labels will be factored out and only the labels of ml/hour will be left over.

    0.5 mg/1 minute (dose desired) x 500 ml/0.9 gram (dose on hand) x 60 minutes/1 hour (conversion factor) x 1 gram/1000 mg (conversion factor) = 16.666 ml/hour = 17 ml/hour (rounded off)
    an iv of d5w containing 2 mg of epinephrine and a total volume of 250 ml is to be infused at a rate of 15 mcg per minute. at how many ml per hour will you infuse the iv.
    this is the same kind of problem with different labels attached to the numbers.
    terms you will need for this calculation
    dose desired: 15 mcg/1 minute (given information)
    dose on hand: 250 ml/2 mg (given information)
    conversion factor: 60 minutes/1 hour (to convert minutes to hours)
    conversion factor: 1 mg/1000 mcg (to convert mg to micrograms and vice versa)

    put each of these relationships (ratios, fractions) into a equation in a way (one label in a numerator and it's match in a denominator) that the unwanted labels will be factored out and only the labels of ml/hour will be left over.

    15 mcg/1 minute (dose desired) x 250 ml/2 mg (dose on hand) x 60 minutes/1 hour (conversion factor) x 1 mg/1000 mcg (conversion factor) = 112.5 ml/hour = 113 ml/hour (rounded off)
    an iv of d5w containing 2 mg of isuprel and a total volume of 250ml is to be infused at a rate of 1 mcg per minute. at how many ml per hour will you infuse the iv?
    again, this is the same kind of problem with different labels attached to the numbers.
    terms you will need for this calculation
    dose desired: 1 mcg/1 minute (given information)
    dose on hand: 250 ml/2 mg (given information)
    conversion factor: 60 minutes/1 hour (to convert minutes to hours)
    conversion factor: 1 mg/1000 mcg (to convert mg to micrograms and vice versa)

    put each of these relationships (ratios, fractions) into a equation in a way (one label in a numerator and it's match in a denominator) that the unwanted labels will be factored out and only the labels of ml/hour will be left over.

    1 mcg/1 minute (dose desired) x 250 ml/2 mg (dose on hand) x 60 minutes/1 hour (conversion factor) x 1 mg/1000 mcg (conversion factor) = 7.5 ml/hour = 8 ml/hour (rounded off)
  5. by   ♪♫ in my ♥
    Having all the problems worked out for you is a double-edged sword. It's not sufficient just to look through and understand the solutions posted. You need to be able to go through and do them yourself from scratch.

    I'd encourage you not to look at all the solutions but only the one for the first problem. Then try to do the second problem using the first one as a guide. If you get hung up, use Daytonite's solution to the second problem only as much as you need. Do the same with the third problem.

    It's one thing to understand how the problem is done. It's another thing to be able to do it yourself from scratch. Make sure you know the difference. Trust me, I speak from the experience of having a solutions manual to my calculus book -- Several times I didn't do my homework but just copied it. I thought, "Oh, that makes sense" but then struggled on the tests.
  6. by   mcknis
    Thanks to both of you for your help. Daytonite, thanks for working out the problems, and Melody in my heart (I think that is what your screen name is, BTW...is that right?) thanks for giving me just one problem. Some people do better by having the answer given to them, but I only the other hand, do not. SO I did figure them out before I got on here and I will post how I did, so you guys can make sure it is done up to par.

    Thanks again,
    Scott

    1) 0.9gm/500ml = 0.0018gm/1ml = 1.8mg/1ml
    1.8mg/1ml = 0.5mg/min/x
    x=0.28ml/min
    0.28ml/min x 60minutes=17ml/hr

    2) 2mg/250ml = 0.008mg/1ml = 8mcg/1ml
    8mcg/1ml = 15mcg/min/x
    x=1.875 ml/min
    1.875ml/min x 60minutes=112.5ml/hr = 113ml/hr

    3) 2mg/250ml = 0.008mg/1ml = 8mcg/1ml
    8mcg/1ml = 1mcg/min/x
    x=0.125 ml/min
    0.125ml/min x 60minutes=7.5ml/hr

    Question: How do you know when to round? When I did the problem before, I was rounding after I solved for X which made my answer off by about 1 ml/hr. I know that the answers I have now are right because they match the examples that the instructor gave to us.
  7. by   Daytonite
    In actual practice it's hard to impossible to set a drip rate or and IV pump at 16.7, 112.5 or 7.5 mL/hour. Also, there are rules of scientific calculation that state that if your problem is presenting the numbers to you as whole numbers, then your answer should be calculated to a certain number of whole digits--or something like that. It mostly applies to how many digits past the decimal you want to go in presenting an answer. Since the numbers in these problems only went to one decimal place, the answer should never have more than one decimal place in them.
  8. by   mcknis
    Thanks Daytonite for the clarification. BTW...are you an RN instructor? Sounds like you may be...or maybe just a well versed nurse. Either way, I know I have heard from many people, that you know your stuff thoroughly!

    Thanks again for the help
  9. by   Daytonite
    No, I am not an instructor. I have been an RN for 32 years. I was, at times a preceptor for new employees or new grads. I've had to deal with my own learning deficits over the years and insatiable about seeking out the "why" of some things. I am just always willing to pass on what I know. I am currently disabled due to multiple medical problems so I have a lot of time on my hands. This is one way I feel I am using my time constructively. Believe me, I know how confusing some nursing subjects can be! I had been contemplating going back to get a Master's Degree and teaching. It may not be feasible as I am facing some pretty serious medical problems right now.
  10. by   mcknis
    I am so sorry to hear that. From the few times I have been able to jump on here during school...I could tell that you were experienced simply by the way you write.

    Thanks for the knowledge bestowed upon us and for any more that may come our way.
  11. by   ♪♫ in my ♥
    Regarding rounding, you should never round inside of a calculation; only round the final answer.
  12. by   mcknis
    Thanks

    Thats were I was getting stuck at!
  13. by   Daye
    Quote from Daytonite
    No, I am not an instructor. I have been an RN for 32 years. I was, at times a preceptor for new employees or new grads. I've had to deal with my own learning deficits over the years and insatiable about seeking out the "why" of some things. I am just always willing to pass on what I know. I am currently disabled due to multiple medical problems so I have a lot of time on my hands. This is one way I feel I am using my time constructively. Believe me, I know how confusing some nursing subjects can be! I had been contemplating going back to get a Master's Degree and teaching. It may not be feasible as I am facing some pretty serious medical problems right now.
    So sorry to hear that, what a wonderful way to continue to contribute! people like you doing that make the experienced nurse a great resource, who ever said nurses eat their young, didn't know you.
  14. by   kstec
    1) 0.9 gm of Cordarone in D5W has been prescribed for IV infusion at a rate of 0.5 mg per minute. The IV solution has a total volume of 500ml.
    The IV should be infused at how many ml per hour?
    Just use your calculator and do exactly as I do below.....

    Take what you want 0.5mg divided by what you have 900mg (0.9g) multiplied by the volume.
    Ex: 0.5 divided by 900mg (0.9gm) X 500ml =.28mg X 60min/hr=16.66
    want have volume
    or 7ml/hr.

    2) An IV of D5W containing 2 mg of epinephrine and a total volume of 250 ml is to be infused at a rate of 15 mcg per minute. At how many ml per hour will you infuse the IV.
    Alway convert first: 2mg=2000mcg

    Ex: 15mcg divided by 2000mcg X 250ml =1.875ml/min or 2ml/min
    want have volume

    3) An IV of D5W containing 2 mg of Isuprel and a total volume of 250ml is to be infused at a rate of 1 mcg per minute. At how many ml per hour will you infuse the IV

    Convert 2mg=2000mcg

    Ex: 1mcg divided by 2000mcg multiplied by 250ml= .125ml
    want have volume
    X60min/hr=7.5ml

    This is the way I was taught to do calculations in pharmacy when I worked there. I work as a LPN now so I do not do these type of calculations anymore so I hope there all correct. But we just used a very simple formula.

    Dose you want divided by have (stock) mulitiplied by quantity/volume.
    Always convert to the same mg/mg or mcg/mcg, etc.

    Good Luck

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