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Hi everyone, can anyone PLEASE explain to me how to solve this question? I will greatly appreciate it.

Order: Magnesium sulfate 40 g in 500 ml IV solution. Start with a bolus of 3 g to infuse over 30 minutes. Then maintain a continuous infusion at 2 g/hr

Rate: ____ ml/hr for bolus ____________ Infusion pump limit

Rate: ____ ml/hr for continuous infusion _____________ Infusion pump limit

593 Posts

Specializes in Cath/EP lab, CCU, Cardiac stepdown. Has 3 years experience.

Find out how much ml is in 1 g first then work from there. Show us what you have so far

104 Posts

Okay but this may look very dumb. I apologize for the confusion in advance :-)

40g/500ml = 3g/x ml cross multiple and I get x = 37.5 ml/hr. So since its 3 g to infuse over 30 mins then its rate is 6 ml/hr. This may be wrong but this is honestly how far I can go. And would the infusion pump limit be 500 ml?

3,833 Posts

You are almost right with the first problem. 37.5 mL is correct, however is this the volume to be delivered, or the infusion rate, to administer a 3 g bolus over 30 minutes? You can work the second problem the same way you did the first. There are, however, other ways in which this problem could be worked.

As SNurseKylam suggests, you could start by determining the volume for 1 g and then work from there. For example, let's assume our infusion contains 1 g in 20 mL. For the first part of your problem you want to administer a 3 g bolus you would need to administer 60 mL. What would the infusion rate be to infuse 60 mL over 30 minutes?

Another way to work this problem use the following formula (D/H) * V where D = the desired dose, H = the dose available, and V = the volume for H. Again, let's assume our infusion contains 1 g in 20 mL. For the second part of your problem you could calculate the infusion rate in the following manner: (2 [D] / 1 [H]) * 20 (V) = 40 mL/hour.

While you are in school your instructor might insist that you work problems using a prescribed formula (ratio proportion, D/H*V, etc.). While it might seem petty, this ensures that you have been exposed to the varied ways of calculating medication math. When you graduate, you will find certain formulae that work best for you.

371 Posts

Specializes in Critical Care. Has 4 years experience.

Wait.. Is no one going to question 40 GRAMS of mag? Am I missing something here?

3,833 Posts

Wait.. Is no one going to question 40 GRAMS of mag? Am I missing something here?

Magnesium sulfate is frequently used in the prevention of preterm labor with a usual loading dose of 4 - 6 g and a continuous infusion of 2 - 3 g/hour.

371 Posts

Specializes in Critical Care. Has 4 years experience.

Ha. Thanks for the clarification, not my area of expertise!

371 Posts

Specializes in Critical Care. Has 4 years experience.

75 ml/hr for 37.5 ml - bolus.

40g in 500 ml comes to 1g in 12.5 ml.

3g bolus is 3 x 12.5 ml = 37.5 ml. 37.5 ml/hr would be the rate if it was over an hour.. Double it since its over half an hour - 75 ml/hr

2 g/hr continuous rate. We know 1g is 12.5 ml, so 2 g/hr is 25/ml/hr.

104 Posts

Okay you guys, this is my answer and I hope I listen to you all.

Order: Magnesium sulfate 40 g in 500 ml IV solution. Start with a bolus of 3 g to infuse over 30 minutes. Then maintain a continuous infusion at 2 g/hr

Rate: 75____ ml/hr for bolus 37.5 ml____________ Infusion pump limit

Rate: 25____ ml/hr for continuous infusion 462.5 ml_____________ Infusion pump limit

104 Posts

Thank you jja224, I did not even see your answer posted because it actually took me this long on pen and paper to do the problem and I did not move off of "post comment". I left it open while I was do this. Thanks a lot.

314 Posts

I like using dimensional analysis :)

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