Dosage Calc, part 30: PCA Pumps

  • 00:00 Intro
  • 2:48 Ex. 1
  • 3:37 Ex. 1A
  • 6:05 Ex. 1B
  • 6:41 Ex. 1B Dimensional Analysis
  • 7:35 Ex. 1B Ratio & Proportion
  • 8:35 Ex. 1B Formula method

Full Transcript: Dosage Calc, part 30: PCA Pumps

Hi, I'm Cathy with Level Up RN. In this video, I will be explaining what a patient-controlled analgesia pump is used for and some of the important settings on a PCA pump. I will then work through an example problem where we calculate the amount of medication administered to a patient using a PCA pump. 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.

Patient-controlled analgesia pumps, or PCA pumps, are devices that deliver analgesic medications, most commonly opioids, to the patient. And they can be programmed with a number of settings that I'm going to go through now. First of all, we have the loading or bolus dose, which is the initial amount of the medication that is provided to the patient. Then we have the demand dose. That is the amount of medication that is provided to the patient when they hit the button on the PCA pump. And then we have the lockout interval. That is the minimum amount of time between demand doses. So during this window, even if the patient hits the button on their PCA pump, they will not get a demand dose of the medication. So for example, if we have a lockout interval of 15 minutes, and the patient hits the button at 9:00 AM and gets a demand dose, if they hit the button again at 9:10 AM, they will not get another demand dose because we're within that 15-minute lockout interval. Okay. And then we may have a continuous or basal rate of medication that is being delivered to the patient. So this is a continuous infusion of medication that the patient is receiving no matter what. They don't need to hit the button to get this continuous rate of medication delivery. And then finally, we have the one or four-hour limits that may be set up. This is the total cumulative amount of medication the patient can receive within either one hour or four hours.

All right. In this problem, we have a patient with the following PCA parameters. They have a basal rate of 25 micrograms per hour, a bolus dose of 30 micrograms, a demand dose of 20 micrograms, and a lockout interval of 10 minutes. Pharmacy has sent us a syringe of fentanyl, 2,500 mcg, and 50 mls of solution to load into the pump. During the first two hours, the bolus dose is administered to the patient, and the patient pushes the PCA button six times at 12:30, 12:35, 12:40, 13:00, 13:30, and 13:50. And we need to round all our answers to the nearest tenth. All right. In part A, we are being asked, how many micrograms of fentanyl did the patient receive during the first two hours? Okay. So let's break this down. They got their bolus dose, right? And their bolus dose was 30 micrograms. Then they got their demand doses. So they pushed the button six times at 12:30, 12:35, 12:40, 13:00, 13:30, and 13:50. However, we have a lockout interval of 10 minutes. That means after they push the button, there are 10 minutes where they will not get a dose, even if they push the button.

So they pushed the button at 12:30, they push it at 12:35, but at this time, a dose was not administered because we were within that lockout interval. Then they got their dose at 12:40. That's fine. That was 10 minutes after this one. 13:00, that's fine. That was 20 minutes. 13:30, that was 30 minutes. That's fine. And 13:50, that was 20 minutes from the last dose, so that's fine. So really, 12:35 is the only dose they did not receive. So they got five of the six demand doses, so they got five doses. And for each demand dose, they got 20 micrograms, so that equals 100 micrograms. And then they are also getting a basal rate infusion. So they're getting a continuous infusion of 25 micrograms per hour. And the question is asking us, how much did they receive during the first two hours? So if we multiply this times 2, that equals 50 micrograms that they got through that continuous infusion or basal infusion. So if we add up these three amounts, we end up with 180 micrograms. And that is the amount of fentanyl that the patient got during those first two hours.

All right. Let's now tackle part B of this problem which asks us, how many milliliters did the patient receive during the first two hours? So let's erase part of my board here. I'm going to leave up the micrograms that the patient received in the first two hours which was the answer to part A because we're going to need that number to calculate part B. Part B can be solved using dimensional analysis, ratio and proportion, or the formula method. So let's first solve this with dimensional analysis. So during the first two hours, our patient got 180 micrograms, like we already calculated with part A. If we take this amount and multiply this times the available concentration, which is 2,500 micrograms in 50 ml, then we can calculate the milliliters. We put the milliliters on top and the micrograms on bottom, and that way, my micrograms will cross off and I'll be left with milliliters, which is what I'm looking for. So if we do this math, we end up with 3.6 milliliters. And that's how much the patient received during the first two hours.

We can also solve this part of the problem using ratio and proportion. So on one side of the equation, if we put the known ratio, which is our available concentration here, and on the other side of the equation, we'll put an X for the unknown amount of milliliters. And then here put 180 micrograms, which is the amount they got in the first two hours. Now I can cross multiply here. So 2,500X equals 50 times 180. So 2,500X equals 9,000. And if I solve for X here, I end up with 3.6 milliliters. So same answers I got using dimensional analysis. And then finally, I can solve this part of the problem with the formula method as well, which is desired over half times the vehicle. So our desired is 180 micrograms. What we have are 2,500 micrograms in 50 mls of solution. That's our vehicle. And again, if you multiply this out, we end up with the same answer again, 3.6 milliliters. So that's the amount of milliliters the patient received during the first two hours.

Back to blog

Leave a comment

Please note, comments need to be approved before they are published.