IV drip rate calculations...HHHEEELLLPPP!

  1. Hi all. I'm a 2nd semester student who has just started his first semester in Pharmacology.

    My Peds teacher (of all people) gave us a math assignment to calculate IV med rates on our first day.

    After much researching and digging into our pharm calc books, nobody in our class can figure out these questions.

    Sorry if these seem elementary for some of you all, but any help is appreciated!!

    Here's 2 of the questions:


    Determine the volume of solution that must be added to the burette to mix the following IV drugs. Then calculate the flow rate in gtt/min for each administration using a microdrip, and indicate the mL/hr setting for the pump.


    1. An IV medication of 75 mg in 3 mL is ordered diluted to 55 mL to infuse over 45 min.
    Dilution volume _________ gtt/min___________ mL/hr_____________



    2. A dosage of 100 mg in 2 mL is diluted to 30 mL of D5W to infuse in 20 min.

    Dilution volume _________ gtt/min___________ mL/hr_____________


    THANKS again, and if someone could show me how you came up with the answers, that would be super helpful.
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  2. 15 Comments

  3. by   Daytonite
    determine the volume of solution that must be added to the burette to mix an iv medication of 75 mg in 3 ml is ordered diluted to 55 ml to infuse over 45 min.


    dilution volume _________ gtt/min___________ ml/hr_____________
    55 ml (total amount desired) - 3 ml (amount on hand) = 52 ml (amount to be added to the burette)

    then, to determine the flow rate using microdrip tubing at gtts/min i like to use dimensional analysis for this because it allows me to work with the labels attached to the numbers so i can see what is happening to them. i want to end up with gtts/min, so i set up the equation so that i am going to end up with "gtts" on the numerator of the answer and "min" on the denominator of the answer. i also include part of the formula of the dose desired divided by dose (or, in this case, the drop factor of the tubing) on hand:
    55 ml/45 min (dose desired) x 60 gtts/1 ml (drip factor of microdrip tubing) = 73 gtts/min (after doing the math, canceling out labels repeated in the numerator and denominator and rounding off the answer)

    if you are using a pump, you would need to determine how much fluid would have to infuse over 1 hour because iv pumps almost always accept programming of only ml/hr. so, this can be accomplished with a simple ratio. if 55 ml is to infuse in 45 minutes, how much would infuse in 1 hour, or 60 minutes? or,
    55 ml/45 min = x ml/60 min, or x = 73 ml (rounded off)
    hmm. notice something here? the drip rate of the microdrip tubing is the same as the hourly infusion rate. keep that in mind. that's an important tidbit to know.
    determine the volume of solution that must be added to the burette to mix a dosage of 100 mg in 2 ml is diluted to 30 ml of d5w to infuse in 20 min.
    dilution volume _________ gtt/min___________ ml/hr_____________

    actually, this is the same problem with different numbers.
    30 ml (total amount desired) - 2 ml (amount on hand) = 28 ml (amount to be added to the burette)

    now, i want to end up with gtts/min again, so
    30 ml/20 min (dose desired) x 60 gtts/ml (drip factor of microdrip tubing) = 90 gtts/min (after doing the math, canceling out labels repeated in the numerator and denominator)

    the pump will be set at:
    30 ml/20 min = x ml/60 min, or x = 90 ml
  4. by   mingez
    Quote from daytonite
    55 ml (total amount desired) - 3 ml (amount on hand) = 52 ml (amount to be added to the burette)

    then, to determine the flow rate using microdrip tubing at gtts/min i like to use dimensional analysis for this because it allows me to work with the labels attached to the numbers so i can see what is happening to them. i want to end up with gtts/min, so i set up the equation so that i am going to end up with "gtts" on the numerator of the answer and "min" on the denominator of the answer. i also include part of the formula of the dose desired divided by dose (or, in this case, the drop factor of the tubing) on hand:
    55 ml/45 min (dose desired) x 60 gtts/1 ml (drip factor of microdrip tubing) = 73 gtts/min (after doing the math, canceling out labels repeated in the numerator and denominator and rounding off the answer)

    if you are using a pump, you would need to determine how much fluid would have to infuse over 1 hour because iv pumps almost always accept programming of only ml/hr. so, this can be accomplished with a simple ratio. if 55 ml is to infuse in 45 minutes, how much would infuse in 1 hour, or 60 minutes? or,
    55 ml/45 min = x ml/60 min, or x = 73 ml (rounded off)
    hmm. notice something here? the drip rate of the microdrip tubing is the same as the hourly infusion rate. keep that in mind. that's an important tidbit to know.



    actually, this is the same problem with different numbers.
    30 ml (total amount desired) - 2 ml (amount on hand) = 28 ml (amount to be added to the burette)

    now, i want to end up with gtts/min again, so
    30 ml/20 min (dose desired) x 60 gtts/ml (drip factor of microdrip tubing) = 90 gtts/min (after doing the math, canceling out labels repeated in the numerator and denominator)

    the pump will be set at:
    30 ml/20 min = x ml/60 min, or x = 90 ml
    thank you soooo much!!! let me see if i can get my fried brain around that.
  5. by   dom7
    Great information! Thanks this helps me as well!!!!

    Can someone explain to me how to calculate the below prolem that I have for a homework assignment tomorrow????

    1. A child weighing 24.4kg has an IV of 250 ml of D5W containing 2500 units of a drug. The dosage range for this drug is 15-25 unit/kg/hr. The pump is set to deliver 50ml/ hour

    Dosage range per hour_________ Dosage infusing per hour__________
    Assessment________
  6. by   Daytonite
    hi, dom7!

    here is how you solve the problem.

    a child weighing 24.4kg has an iv of 250 ml of d5w containing 2500 units of a drug. the dosage range for this drug is 15-25 unit/kg/hr. the pump is set to deliver 50ml/ hour

    dosage range per hour_________ dosage infusing per hour__________
    assessment________
    dosage range per hour: to determine this you need to figure out what the dosage would be for a 24.4 kg child at a dose of 15 units/kg/hr. and at a dose of 25 units/kg/hr. so, you start with a complex fraction that is 15 units/1 kilogram/1 hour. remember that to reduce this complex fraction down you have to multiply both the numerator and the denominator by the reciprocal of the denominator (1/1 hour) in order to make the denominator equal to 1. then, you are going to multiply by the weight of the child which, thank goodness, is already in kilograms or you would have to do a conversion. here's the math:
    15 units/1 kg (first part of the low dose range) x 1/1 hour (that reciprocal! and second part of the low dose range) x 24.4 kg/1 (child's weight) = 366 units (low dose range)


    25 units/1 kg (first part of the high dose range) x 1/1 hour (that reciprocal! and second part of the high dose range) x 24.4 kg/1 (child's weight) = 610 units (high dose range)
    so, the answer to the dosage range per hour is: 366 to 610 units per hour for this child


    dosage infusing per hour: use the formula "dose desired (x) divided by dose on hand (250 ml/2500 units--note i've manipulated what's in the numerator and denominator in order to cancel out labels in the final calculation!) equals the dose to give (50 ml/1 hour)" and plug the figures you have been given into this equation and do a little math manipulation, this is what you end up with:
    x = 50 ml/1 hour x 2500 units/250 ml = 500 units/1 hour (dosage of drug infusing per hour)
    assessment: 500 units per hour is within the safe range of 366 to 610 units per hour.

    welcome to allnurses!
  7. by   L&DRN08
    I too am having some difficulty with some of my calcs! Can someone help me out, I seem to be able to come up with some of the answers in my head, but we need to show our work & I can't put it into an actual "formula" UGGGHHH I am TERRIBLE with math of any sort!
    Any help is greatly appreciated!!
    Here's where I am stuck:

    1. Guaifenesin elixir is labeled 100 mg per 5 ml. How many ml. will contain a dose of 75 mg?

    2. The infusion pump is prepared with 50 mg of Demerol in 50 ml of N/S. How many ml per hour should be infusion pump be set to deliver

    2 mg of Demerol per hour?
    This is one of those that I can figure out in my head....I know it would be 2mL/Hr, but I don't know how to work it out on paper!!

    3. The doctor orders Amoxicillin 500 mg IVPB q12h. After reconstitution with 10.5 ml sterile water, the drug concentration available is 1 gm per 5 ml. How many ml contain the correct dose?

    4. An IV of Keflin 500mg is mixed in 50cc of D5W. How many ml/hr
    will you set the infusion pump to complete the infusion pump in 30 minutes?


  8. by   Daytonite
    guaifenesin elixir is labeled 100 mg per 5 ml. how many ml. will contain a dose of 75 mg?

    set up a simple ratio equality.
    100 mg/5 ml = 75 mg/x ml and cross multiply the numbers, so that x = 3.75 ml
    the infusion pump is prepared with 50 mg of demerol in 50 ml of n/s. how many ml per hour should the infusion pump be set to deliver 2 mg of demerol per hour? this is one of those that i can figure out in my head....i know it would be 2ml/hr, but i don't know how to work it out on paper!!
    you can see this work out easily with dimensional analysis which is also called the factor label method. in this method you are seeking to remove repeated labels attached to numbers in the terms. in this case, the label "mg" appears in the numerator and denominator of two terms of the equation and cancel each other out (they factor out). you also employ the old "dose desired divided by dose on hand" formula. remember that this creates complex fractions (a fraction over a fraction), but because you are manipulating where the labels are occurring on these fractions it really doesn't matter which number is in the numerator or denominator except where it affects the factoring out of the label attached to the number. like this. . .
    2 mg/1 hour (dose desired) x 50 ml/50 mg (dose on hand) = 2 ml/1 hour
    the doctor orders amoxicillin 500 mg ivpb q12h. after reconstitution with 10.5 ml sterile water, the drug concentration available is 1 gm per 5 ml. how many ml contain the correct dose?
    the problem is telling you that there is 1 gram of amoxicillin in 5 ml after reconsititution. the 10.5 ml of sterile water is a red herring and designed to throw you off track. the problem is really quite simple.
    500 mg (dose desired) x 5 ml/1 gram (dose on hand) x 1 gram/1000 mg (conversion factor) = 2.5 ml
    an iv of keflin 500 mg is mixed in 50 cc of d5w. how many ml/hr will you set the infusion pump to complete the infusion pump in 30 minutes?
    another ratio. most iv pumps have to be programmed in ml per hour. so, if you are going to give 50cc (or ml) over 30 minutes, that would be how many cc (or ml) over 60 minutes (1 hour)? set up a ratio and cross multiply.
    50 cc/30 minutes (dose to give) = x cc/60 minutes, so x = 100 cc (or ml)
  9. by   L&DRN08
    Thank you so much. You are always so helpful. This makes was a great help. Calculations are my biggest struggle, I've always had trouble with math which makes this difficult even when I can figure out how to set up the correct formula.
    I'm glad that you mentioned that the 10.5mL of sterile H2O was a distractor...because I thought it was!!
    Thaknks again.
  10. by   MySimplePlan
    Daytonite for President!!!!
  11. by   mrsbigwood1
    Help!! I don't think I have enough info to answer this

    A 2-year old is to receive 200 mg. of Ampicillin IV. The bottle arrives from pharmacy and has 250 mg. of Ampicillin powder in it.

    A. How much normal saline will the nurse use to dissolve the powder?


    B. How many mls. of Ampicillin will the nurse administer?


    C. The Ampicillin is to infuse over 15 minutes. The nurse will set the hourly rate of the med-infusion pump at what rate? (How many ml/hour in order for the volume to infuse in 15 minutes).
  12. by   Daytonite
    Quote from mrsbigwood1
    Help!! I don't think I have enough info to answer this

    A 2-year old is to receive 200 mg. of Ampicillin IV. The bottle arrives from pharmacy and has 250 mg. of Ampicillin powder in it.

    A. How much normal saline will the nurse use to dissolve the powder?


    B. How many mls. of Ampicillin will the nurse administer?


    C. The Ampicillin is to infuse over 15 minutes. The nurse will set the hourly rate of the med-infusion pump at what rate? (How many ml/hour in order for the volume to infuse in 15 minutes).
    Can't help you. There is missing information here. The bottle of Ampicillin should come with instructions on how much NS to use to reconstitute the powder. Without that information I can't work the problem.

    This sounds like something that is facility specific. If you have a facility medication policy manual that you are supposed to refer to you will find the amount of NS you are supposed to use to reconstitute this Ampicillin. I would also assume that the reconstituted medication is then going to be given by syringe pump????

    Too much missing information here to be able to help you out. Sorry.
  13. by   mrsbigwood1
    Thanks for your input...it turns out it was a trick problem I didn't see your post till tonight but I put that there was not enough info.
  14. by   AliRae
    Quote from mingez
    My Peds teacher (of all people) gave us a math assignment to calculate IV med rates on our first day.
    I know you've gotten the info to help you with the math, but I just had to comment quick on the "peds of all people" giving an IV calc question ... it's because there is no such thing as standard dosing in peds. People from the adult world don't understand us. They think in terms of vials, we think in terms of kilos. Everything in the peds world is based on and calculated using the kid's weight. You do more med calculations in peds than pretty much anywhere, as far as I know. =)

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