Hi, this is Cathy with Level Up RN. In this video, I'll be working through a dosage calculation problem that involves the administration of magnesium. And I'll be solving this problem on my whiteboard using three different methods including dimensional analysis, ratio and proportion, and the formula method. You can find all the information that I'll be covering in this video in our Level Up RN dosage calculation workbook. If you are in nursing school, then you know how important it is to master dosage calculations, and our workbook will help you do just that. In a nutshell, our workbook contains all different types of dosage calculation problems that you are likely to encounter in nursing school. And we demonstrate how to solve each problem using multiple methods so you can pick the way that makes the most sense to you.
So magnesium is a key medication that is administered frequently in maternity nursing. It's used to prevent preterm labor, and it can also be used to treat preeclampsia. Typically, the provider will order a bolus dose of magnesium followed by a continuous infusion of magnesium. Okay. So with this problem, we have an order to administer 5 grams of magnesium sulfate IV bolus over 30 minutes. Once the bolus is complete, we need to start a continuous IV infusion at 2 grams per hour. And magnesium sulfate 20 grams in 500 mls is available. We need to round all of our answers to the nearest whole number. Okay. Part A is asking us how many milliliters are required to administer the correct dose for the bolus. So for part A, we can solve this with dimensional analysis, ratio and proportion, or the formula method. So let's first use dimensional analysis.
So with this method, I'm going to start with what is ordered, which is 5 grams, what is ordered for the bolus. And then I'm going to multiply it by the available drug concentration, which is 20 grams in 500 ml. But I'm going to make sure my mls is on top and my 20 grams is on bottom, such that my grams will cross off, and I'll be left with milliliters, which is what I am looking for. So if you multiply this out, you end up with 125 milliliters. And that's the answer to part A. We could also solve this same part A with ratio and proportion. So with this, on one side of the equation, we would put our known ratio, which is our available concentration, 20 grams in 500 ml. And then on the other side, we would put our ordered dose of 5 grams and put an X for the ml because that's what we're looking for. So we would cross multiply next. So 20 times X equals 500 times 5, so that's 2,500. And if we solve for X, we end up with 125. So again, we come up with the same answer we did here for dimensional analysis. We can also use the formula method to solve this. So with the formula method, we have desired over have times the vehicle. So our desired or ordered dose is 5 grams, and what we have is 20 grams in 500 mls of solution. So our grams will cross off. If we multiply this out, again, we get 125 mls. So that's part A.
Part B is asking us, what is the IV pump rate in milliliters per hour to administer the bolus? So per the order, we need to give the bolus over 30 minutes. So we're going to be giving that 125 milliliters over 30 minutes, but we want to get our rate in milliliters per hour. So 30 minutes is equal to 0.5 hours, right? So if we take 125 milliliters from part A, divide that by 0.5 hours, which is 30 minutes, we would get a IV pump rate of 250 milliliters per hour. Okay. And that is the answer to part B. All right. Let's go ahead and erase our work here to work through Part C. All right. Part C is asking us, what is the IV pump rate in milliliters per hour for the continuous infusion? So per our order, our continuous IV infusion rate should be 2 grams per hour, but we want to get to milliliters per hour. So using dimensional analysis first, I would write down the ordered rate, which is 2 grams per hour. And then I would multiply times the available concentration to get to milliliters per hour. So I would make sure my milliliters is on top here, and my grams are on bottom such that my grams will cross off here, and I'll be left with milliliters per hour. And if you multiply this out, we end up with 50 milliliters per hour. So that's the answer to part C using dimensional analysis.
Right. Let's now solve this same part using ratio and proportion. So our ordered rate is 2 grams per hour, but we want milliliters per hour. So we need to figure out how many milliliters contains 2 grams. So we would set up our ratios. On one side of the equation, we would put our known ratio, which is our available concentration. And then on the other side of the equation, we would put how many grams we're looking for and an X for the unknown, which is the milliliters. So here we would cross multiply. So 20X equals 500 times 2, so that's 1,000. And if you solve for X, we end up with 50, so 50 milliliters. So 2 grams is in 50 milliliters. So if we want to give 2 grams per hour, that's going to be 50 milliliters per hour. And that is the answer for part C using ratio and proportion. And then we can also do this with the formula method. Again, we want to figure out how many milliliters it takes to give 2 grams. So we want desired over have times vehicle. So our desired is 2 grams, and what we have are 20 grams in 500 mls. And our grams will cross off. We multiply this out. We end up with 50 milliliters. So again, the ordered rate was 2 grams per hour. We know to get 2 grams, we need 50 milliliters, so that would be 50 milliliters per hour. And again, it's the same answer we got each of these ways. So whatever your preference is and whatever makes the most sense to you is the method you should use.
