Prehospital Academy Lesson 12.10
Paramedic Med Math
Welcome back! Let's continue our advanced pharmacology lecture with everyone's favorite subject: med math. An important precursor note here to medication math, or med math: there are numerous ways to get to the right answer. I don't propose that this is the only solution for med math, but what I provide you in this lecture is one way of doing med math to ensure that you get the right answer. If you don't have an already established comfort with mathematics, I would encourage you to follow this method so that we can help you and coach you along the way and provide relevant examples that use this method to help you learn this process.
Math is a subject that most people, dare I say all, have some level of discomfort with. The intention of you being comfortable with mathematics and med math is going to be critical to your functioning as a paramedic in the field or even an advanced EMT, as you're going to have to calculate medication doses to administer to your patient. Even if you're using a calculator, if you have no concept of what the average dose should be or a close be able to get a close guess within your head to check your own med math, you run the risk of giving patients erroneous doses and medication errors that can ultimately be lethal. So let's break into med math. We'll start slow and we'll follow this lecture up with a few practice practice questions that we can do together. I'll try and perform some examples as we go along today as well.
Core Mathematical Concepts
Let's start with some terms. In mathematics review, fractions are going to represent a portion of a whole number. So for example, the fraction 1/4 represents one-fourth of 1. It can also be expressed in a decimal form as 0.25. Decimals distinguish numbers that are greater than zero from numbers that are smaller than zero. Percentages, much like fractions or decimals, are expressed as part of 100. The definition "percent" means "per 100." So for example, if we talk about 75%, another way of expressing 75% as a fraction would be 75 of 100 parts, or 75/100. We could also express that in decimal terms as 0.75.
The Metric System in EMS
In med math, we're going to use the metric system. They're base multiples of 10, and we use measurements of length (meter), volume (liter), and weight or mass (gram). You'll need to commit to memory the ratios of liter to milliliter, gram to micrograms, and kilogram. Drugs are packaged in a variety of weights and volumes, and you need to be able to work interchangeably between these because your ordered dose may not be in the same dose that your medication is packaged in. This is particularly true when we talk about dealing with pediatric patients.
The Medication Calculation Formula
Desired Dose = (Concentration) X ( Weight (kg)) X((gtts) / mL)
This is the full formula, but you're not going to use all pieces of this formula for every medication calculation. It is derived based on what your order is requesting.
Bolus Medications
For a bolus medication, you would only need to use Desired Dose / Concentration. For example, if your desired dose is 4 mg and your concentration is 10 mg in 10 mL, you would set up your equation, solve for a single unit of volume (1 mg/mL), and then calculate the volume to administer (4 mL).
Weight-Based Bolus
For a weight-based bolus, you add the weight to the formula: (Desired Dose / Concentration) X (Weight (kg)). For example, to give a 1 mg/kg bolus to a patient weighing 25 kg with a concentration of 1 mg/mL, you would calculate (1 mg/kg / 1 mg/mL) X (25 kg) = 25 mL.
Infusions
For infusions, you use the full formula. For a non-weight-based infusion, the formula is Desired Dose = (Concentration) X ( Weight (kg)) X((gtts) / mL). For a weight-based infusion, you use the entire formula.
Critical Thinking Questions
You need to administer 50 mg of a drug that comes in a concentration of 25 mg/mL. How many mL will you administer?
A patient weighing 150 lbs needs a medication at a dose of 2 mg/kg. The medication is supplied as 100 mg in 10 mL. How many mL will you administer?
You are ordered to infuse a medication at 10 mcg/kg/min for a patient weighing 200 lbs. The medication is supplied as 400 mg in 250 mL of D5W. Using a 60 gtt/mL drip set, what is your drip rate?
Why is it important to always double-check your medication calculations, and what are some strategies you can use to prevent errors?
Explain the difference between a bolus and an infusion. Provide an example of a clinical situation where you would use each.