Download the questions and work along with Cathy as she goes through a number of Nursing Dosage Calculations problems. You can also download the answer key!
Cathy Parkes BSN, RN, CWCN, PHN:
In this video series, I'm going to work through some dosing calculations. For those of you who can use a little extra help with that, I have nine problems that I'm going to work through. I have these problems posted on my website, LevelUpRN.com. You can print them out from my website and kind of work through them alongside me.
I also have the answer key. If you want to work through the problems independently and just check your answers, then you can just open the answer key and see how you did. I'm just going to take one problem at a time and I'll show you how I like to go through the problems.
The first problem I'm going to go over is how to calculate an oral dose. If your doctor prescribes like a tablet or a capsule, how do you calculate how many tablets or capsules your patient should get? In this particular problem, the order was for 0.4g of this medication, every 8 hours. What we have on hand are capsules with 200mg in each capsule. Let's work through this. What we need to give the patient is 0.4g. I can already see that because my capsules are in milligrams, I'm going to need to convert these grams to milligrams. I'm going to multiply. 1g is equal to 1000mg. At this point I can cross off this gram and this gram. One's on top, one's on bottom. I have milligrams. Now I need to figure out how many capsules my patient should get. I would multiply this. 200mg are in one capsule. my milligrams are going to cross off. then I would do my multiplication, which is 0.4, times a thousand, and then divide by 200. that would give me two capsules that I need to give my patient for the dose that is ordered. That's problem one.
Now I'm on Problem #2.We are going to calculate an oral dose again, but this time we have an order for a liquid medication. In this particular case, we have an order for 0.5g of a liquid medication to be administered every 12 hours. what we have available is this medication, in the following concentration. We will have 250mg within 5m of liquid. The question is, how many milliliters should we administer? Again, I'm going to start with what's ordered, which is 0.5g. you can see by what's available that I'm going to have to convert again to milligrams. I'm going to multiply 1000mg over 1g, and now I have milligrams, but I need to find out how many milliliters I need to give the patient. I'm going to multiply this times 250mg is in 5ml. I can cross off my milligrams, and if I multiply this out. I will get milliliters. in this case, I get 10ml. You can do this with your calculator. You would multiply 0.5 times 1000 times 5 divided by 250. that will give you 10ml. Again, I'm starting with the ordered dose and I'm just doing conversions to get to the unit of measure that is asked for in the problem. That is Problem 2.
We'll pick it up with Problem #3 next. The third type of problem I'm going to work through here is calculating an IV, IM, or a subcutaneous dose. In this particular example, the doctor has ordered 5,000 units of heparin to be given every 8 hours. What we have on hand are 10,000 units/ml. Per milliliter of liquid, there are 10,000 units of heparin, and we want to know, how many milliliters should we give with each dose? And then how many milliliters we're going to give over that 24 hour period. Let's first talk about what we're going to be giving per dose. Again, the order is for 5,000 units and what we have is 10,000 units in 1ml. Our units cross out here, we take 5,000 divided by 10,000 and we get 0.5ml. That's how much we're giving with each dose We're giving that every 8 hours. To calculate how many milliliters we're going to give over a 24 hour period, we're going to take that 0.5ml that we are giving per dose. We're giving that every 8 hours and we're going to multiply that times 24 hours. Our hours cross off. we're going to end up with, if you do the math here, 0.5 times 24, divided by 8 ends up being 1.5 milliliters total, that we're giving over a 24-hour period. That is Problem 3, we will move on to Problem 4 next.
Cathy Parkes BSN, RN, CWCN, PHN:
Continuing on with our dosing calculations!
I'm on Problem #4, which deals with how to calculate dosing based on a patient's weight. In this particular problem, the patient weighs 150lbs and the order is for 0.3ml/kg of body weight. You can already see we're going to have to convert pounds to kilograms. Let's go ahead and do that first. 150lbs, and then 1kg has 2.2lbs. This is a conversion factor that you absolutely have to know, and you're going to be using it repeatedly when you're doing dosing calculations. This will give me kilograms. How much the patient weighs in kilograms. Then the order is for 0.3ml/kg. If we take 1kg, 0.3ml/kg, then our kilograms cross out and we're left with milliliters. Now, pay close attention to this question. They asked us, "how many milliliters should the patient get?" It also told us to round to the nearest 10th. It's really important to pay attention to a rounding instruction in the question. Sometimes it will tell you to round to the nearest whole number, sometimes it'll tell you to round to the nearest 10th. You've got to make sure you pay attention to that and do exactly that. Because you can do all your calculations correctly, then if you round wrong at the end, you're going to get the problem wrong. We definitely don't want to get the problem wrong. When we do this, we should get our milliliters. If I get out my handy dandy calculator here, and I take 150 divided by 2.2, multiply times 0.3, I get 20.45454545, like repeating on and on. Because I'm rounding to the nearest 10th, I would end up with 20.5ml. Not 20.45. Not just 20, we need to go to the 10th. It ends up being 20.5ml in this problem. We'll pick it up with the fifth problem next.
Now I'm going to go over Problem #5, which is another problem where we're calculating the dose based on the patient's weight, but it's a little more complicated and we're going to have to go through multiple steps to kind of work through the problem. In this particular problem, the doctor has ordered 12mg/kg/day, and it needs to be divided into doses every 8 hours. Our child weighs 22lbs, and what's available in terms of the medication is 200mg/5ml. The question is, how many milliliters do we administer per dose? Not for the whole day, but per dose. We know our child weighs 22lbs and our order is in kilograms. Right off the bat, we're going to have to convert to kilograms. We're going to take the child's weight, 22lbs, and we're going to multiply times 2.2lbs in 1kg. That will give us the child's weight in kilograms. then we know we're giving 12mg/kg/day. If we take that for each kilogram, we're going to be giving 12mg. If we do this math, we end up with-- Well, first of all, we cross off our kilograms and we should end up with milligrams per day. We ended up with 120mg for the day. But the question is per dose, versus for the day. We also need to know the milliliters. we're giving 120mg over a 24 hour period, but we really want to know how much we need to give every 8 hours cause that's what's ordered. We're going to cross off these hours and we're going to end up with 40mg per dose. Every 8 hours, we're going to give that child 40mg. But again, we're asking for milliliters. That's where we have to look at the medication we have available in what concentration. We take the 40mg, and we have 200mg in 5ml. I want the milligrams to cross off and I want to end up with milliliters. I'm going to put the 200mg on the bottom, put 5ml on top, cross off my milligrams, do that math. I ended up with 1ml per dose, which is every 8 hours. Again, I know it's a lot of different steps. We're really just trying to go with the units of measure we're given, and then work our way towards what's ordered to be able to answer the question. Just to review with this one again, we took the weight, we calculated the child's weight into kilograms, and then we found out how many milligrams they needed for the day. Then we multiplied this times 8 hours to find out how much we give per dose. Then we took that with the medication we have available to find out how many milliliters we need. That is Problem 5, probably the hardest one that I'm going through today. But we've got a few more that I'm going to go through. Hang in with me and we'll do some more. Thanks!
Cathy Parkes BSN, RN, CWCN, PHN:
I'm going to go over some IV pump calculations now. Problem #6 has an order for 1000ml of some kind of IV fluid to infuse over 6 hours. What is the pump rate in ml/hr? And we want to round to the nearest whole number. Again, if you don't pay attention to that and you don't round, then that's going to be a problem and you're going to get it wrong. This one's pretty easy. 1000ml is going to infuse over 6 hours. If we just do this division, we'll get the rate in ml/hr. Turn on my calculator here... 1000 divided by 6 equals 166.66666, on and on. But again, we're rounding to the nearest whole number. That would be 167ml/hr. That was not too bad, especially after the last one.
We'll pick it up with Problem #7 next. #7 deals with another IV pump calculation. In this scenario, our pump is running at 125ml/hr. The question asks us, “how many hours will it take for 500ml to infuse?” We have 500ml and we are infusing at 125ml/hr. We can cross off our milliliters and we'll end up with hours as our unit of measure, which is what it's asking for here in the question. If I do this calculation, I end up with 4 hours. At this rate, it will take 4 hours for 500ml of fluid to infuse into the patient. That is #7.
We'll pick it up with Problem #8 next. #8 deals with drop factor calculations. In this problem, we have an order to infuse 500ml of normal saline over a 4 hour period of time. In this scenario, we don't have an Alaris IV pump. What we have is a drop factor of 12gtt (that means drops) per milliliter, as far as the tubing set up. We want to know how many drops per minute should be delivered to the patient. Again, this is a scenario where we don't have an IV pump and we have to manually adjust the IV bag and the tubing to deliver a certain drop factor. Let's work through this problem. We want 500ml infused over 4 hours, and we know our drop factor is 12gtt/ml. Our milliliters cross off here and we have drops per hour, but we want drops per minute. We're going to have to say 1 hour equals 60 minutes, to allow us to cross off our hours. Here we can see when we multiply this out, and divide, that we'll end up with drops per minute. If you do that, you end up with 25 drops per minute. Again, we're taking the order and we're just using converting factors to get to the unit of measure that is requested in the problem. In this case, drops per minute. That's #8, hopefully that was helpful.
And we've got one more, Problem #9 next. This is the last problem I'm going to go over in this video. It's #9. This is a problem that deals with calculating how much IV fluids a patient is getting in total, when they're receiving multiple infusions. In this problem, we're told that the patient is getting normal saline infused at 50ml/hr in one of their IVs. Then in another IV, they're getting an IV antibiotic infused every 8 hours. This particular antibiotic is in 100ml of fluid. Then they're getting a second IV antibiotic, every 12 hours. This antibiotic is in 50ml of fluid. The problem asks, "How much IV fluids will the patient get in 24 hours?" We're going to handle each of these separately to figure out how much they're getting of each of these within a 24 hour period of time, and then add those together. For the normal saline, we know that the patient is getting it at 50ml/hr. If we multiply times 24 hours, cross off our hours, that will give us how many milliliters they're going to get over 24 hour period of time. If we do that math, we end up with 1200ml. Next, let's handle the next antibiotic. With that antibiotic, they're going to be getting 100ml of fluid every 8 hours. Over a 24 hour period of time, we're going to be getting 300ml again, the hours cross off here, and we're left with milliliters. Then for the second antibiotic, we're going to be getting 50ml of fluid every 12 hours. Again, if we multiply that times 24 hours, we're going to end with 100ml. When we're calculating how much they get total, as far as fluids, within a 24 hour period, we just add 1200 to 300, which is 1500, plus another 100, is 1600ml total. That is it! We got through all nine practice questions.
I tried to pick a variety of questions that I've seen previously that I think are important for you to know. However, if I have missed a certain type of problem, or there's another type of problem you want me to work through, then definitely leave that in the comments. I'm happy to make another video or two or, or more, as many as are needed so that you guys can really understand how to do these math questions, because I really don't want you to miss any of these math questions on your test.
On your nursing school exams, there will always be these random questions that hardly any nursing student gets right. We need to save our points for those kinds of random, crazy questions. We need to try to get all our math questions right, all our ABG interpretation questions right. That way we save our points for those really difficult questions that are hard for anyone to get right. Hope this video series has been helpful. Again, if you have additional problems or additional questions, you want me to work through, leave them in the comments. Thanks so much for watching!