Dosage Calc, part 1: Overview of Methods & Key Points

  • 00:00 What to expect
  • 1:10 Dimensional Analysis
  • 2:00 Ratio and Proportion
  • 2:43 Formula Method
  • 3:34 Key Points

Full Transcript: Dosage Calc, part 1: Overview of Methods & Key Points

Hi, I'm Cathy with Level Up RN. This is the first video in our comprehensive dosage calculation video series. In this video, I will be providing an overview of the three main methods for solving dosage calculation problems, including dimensional analysis, ratio and proportion, and the formula method. I will also be going over some key points that you definitely have to know when solving dosage calculation problems. 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 the first method I want to talk about here is dimensional analysis. It's actually my personal favorite. With dimensional analysis, one equation leads to the answer. So it is the most efficient way to solve dosage calculation problems. One thing with this method, though, you need to keep in mind is it matters greatly what you put on top and what you put on bottom for each component of the equation. So you need to place the units so that like units cross off, and you are left with the units you are looking for. So if I reversed this ratio and had milligrams on top and tablets on bottom, it would not work out. So it matters how you place your units.

The second method I want to talk about is ratio and proportion. This is where you compare a known ratio to another ratio with an unknown component, okay? And then you would take these ratios, and you would cross-multiply. So I would take 30 times X and 0.3 times 40, and then you would solve for X. So if you are a fan of algebra, then this may be your preferred method. One thing to keep in mind is that it often takes multiple steps to solve a dose calculation problem using ratio and proportion.

And then the last method I want to talk about is the formula method. The formula method has the following formula: desired over have times vehicle. So this is the desired dose over the dose you have, and the vehicle is the form and amount that that dose comes in. So this is a very basic formula, and for very basic dose calculation problems, this is an efficient way to solve the problem. However, this method cannot be used with more complicated dose calculation problems. So if your school or program really sticks to very basic problems, you can totally use this, but if your school gets into more complicated problems, this is not going to be an option for many of those problems.

All right. Let's now go over some key points to definitely keep in mind as you are solving these dose calculation problems. The first is units of measure. So you will see a lot of problems that have milligrams, grams, milliliters, and liters. Those are really common units of measure. However, you will sometimes be thrown a different type of unit of measure that maybe you're not familiar with, which can include micrograms or milliequivalents or units, and a lot of students will freak out when they see these new types of units, but I'm here to tell you that you're going to solve the problem in the exact same way as you would with the unit you're more familiar with, like with the milligrams. So don't freak out when you see milliequivalents or micrograms. We're going to solve things in the same way.

The second key point I want to share is it's important to focus on what matters. So in a lot of dose calculation problems, they will throw lots of numbers at you. They'll say, "Reconstitute this vial with 9 milliliters of normal saline for this concentration, and then administer it over five minutes, and do this and this." A lot of numbers, and it can be overwhelming, but you really want to focus on the numbers you need to solve the problem at hand. So read the question carefully, and only consider the numbers you need to consider to answer that question. Chances are, you're going to be able to ignore a lot of the numbers they threw your way, so don't get overwhelmed with all those numbers.

Next, let's talk about leading and trailing zeros. So our little trick to help you remember this concept is that you want to be a leader and not a follower. So what do I mean by this? If we have a number, let's say 0.5 milligrams, this is the correct way to write this number. We would not want to write it like this because-- let's say that decimal point is really faint and not easy to see. If someone looked at that, and they may think it just says 5 milligrams, well, that's very different than 0.5 milligrams. So we want to make sure we include that zero before the decimal point to make it very clear that we're talking about 0.5 milligrams and not 5 milligrams. We also don't want a trailing zero as well because if you look at this, if that decimal point wasn't totally clear, then we could be administering 50 milligrams of a medication when we really meant 0.5, like half of a milligram. So no trailing zeros. We want the leading zero. No trailing zeros. This is the correct way to write that number.

Next, let's talk about rounding. So rounding can get a lot of students in trouble. So you could solve the problem perfectly, go through all the steps exactly as you should, and if you get to the end and round your answer incorrectly, you will get it wrong. And that is so frustrating, so definitely make sure you pay attention to the rounding instructions and round appropriately. So let's take the following example here. Let's say we solved a problem, and we ended up with 1.3455, and we want to round this number to the nearest 10th place. So we want to round to the nearest 10th, so we only need to consider the digit next to the 10th place. And because this is a 4, we're going to keep this number at 1.3. So that would be the correct way to round this number to the 10th place. How would we do this incorrectly? So sometimes students will be like, "Oh, well, 5 rounds up to-- makes this round up to 6, and then this 6 makes this round up to 5, and that 5 would make this round up to 4, so now I have 1.4." You don't want to do that. You don't need to consider any of these other numbers beyond the 100th place. So again, just to reiterate here, if we want to round to the nearest 10th place, we only need to look here. We do not care about these numbers, okay? So that's rounding.

All right. And then the last key point I want to make here is to check for plausibility. What I mean by that is if you do a dosage calculation problem and your answer requires you giving the patient 10 tablets or multiple vials of a medication, chances are you have made a mistake along the way. So you're definitely going to want to go back and check your work.

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