Basic Drug Calculations : Basic Drug Calculations By Steve Kipp, EMT-P I/C
Sanilac Medical Services,
MI.
Introduction : Introduction Did you ever hear someone say in high school “I’ll never use algebra again”? Well, if you’re a paramedic that calculates drug infusions, then you use at least a little algebra. However, the one thing it is not, is ROCKET SCIENCE!!
Slide 3 : There are many theories, formulas, and shortcuts to finding the right answer for drug infusions. In fact, people so hate to memorize an algebraic formula that they memorize twice as many shortcuts. My advice is three-fold.
1) Do what works for you
2) Keep it simple
3) If you’re having trouble, just stick with one
method and master it.
Slide 4 : I will present the formula here that I like to use. As I said before, if you have a method that works for you, then use that. As long as we both come up with the same (correct) answer, the patient will survive.
A formula : A formula Here’s the formula I like to use:
Desired dose X Weight X Drop set
---------------------------------------- = drops
Drug (on hand) / Fluid per min.
Slide 6 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. This formula is derived directly from the Dose on Hand method taught in many paramedic textbooks. But, instead of this being a 5 or 6 step process, it is a 5 part formula.
Memorize these 5 parts, and you’ve got it !!!
Slide 7 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. To explain the parts:
Desired Dose – the dose that is ordered; such as 2 mg/min, 5 mcg/min, 7 mcg/kg/min, etc.
- Write ONLY the number that represents the dose you want. If the dose you want is 7 mcg/kg/min, then just write 7.
Hint: mcg = micrograms
Slide 8 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. To explain the parts:
2) Weight – Write the patient’s weight in kg. Kg is the unit of weight that pretty much all drugs these days are ordered by, so get used to it. If you are provided a weight in pounds, then divide pounds by 2.2 to get kg.
- If the drug is not weight dependent, then leave this number out of the formula. It’s that easy!
Hint: kg = kilograms
Slide 9 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. To explain the parts:
3) Drop set: Write the SIZE of the drop set you are using. If it’s a 60 drop set, write 60.
- This number is what makes the entire formula equal a drops per minute value. In other words, if you leave this number out, such as when you use an I.V. pump, then the entire formula equals cc’s per minute.
Hint: cc = ml
Slide 10 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. To explain the parts:
4) Drug on hand: This is what you’re taking out of the box. Look on the vial, pre-filled syringe, etc. and see how much drug you’re holding. It may be 1 gram of lidocaine, 200 mg of dopamine, etc. It would be best if you would make sure, at this point, that your drug on hand matches the UNIT of your desired dose. I’ll explain how 2 slides from now.
Hint: 1 gram = 1000 mg; 1 mg = 1000 mcg
Slide 11 : 1) Desired dose X 2) Weight X 3) Drop set
----------------------------------------------------------------- = drops
4) Drug (on hand) / 5) Fluid per min. To explain the parts:
5) Fluid: This is what you’re mixing your drug into. It may be a 500cc bag of D5W, a 250cc bag of normal saline, a 50cc syringe, or whatever you choose. Write the volume.
Slide 12 : Desired dose X Weight X Drop set
----------------------------------------------------------------- = drops
Drug (on hand) / Fluid per min. To make your drug on hand match your desired dose:
If your desired dose = 4 mg, and your drug on hand = 1 gram, just add “000” after the “1”, and you’ve made your conversion. This is because 1 gram = 1000 mg.
If you do this in reverse order, 1000 mg to 1 gram, it becomes an issue of a decimal point. Don’t get yourself confused with that if it’s not necessary.
Slide 13 : Another example:
If your desired dose = 4 mcg, and your drug on hand = 1 mg, just add “000” after the “1”, and you’ve made your conversion. This is because 1 mg = 1000 mcg.
Just remember:
1 gram = 1000 mg
1 mg = 1000 mcg Desired dose X Weight X Drop set
----------------------------------------------------------------- = drops
Drug (on hand) / Fluid per min.
Slide 14 : Let’s try one!!
You are ordered to give a Lidocaine infusion at 2 mg per minute. You have a 60 drop set, 1 gram of Lidocaine, and a 250cc bag of D5W. How many drops per minute? Plug the numbers into the formula below:
2 X 60 (leave out the weight for Lidocaine) = 120
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1000 mg divided by 250 = 4
120 divided by 4 = 30 drops per minute. Desired dose X Weight X Drop set
----------------------------------------------------------------- = drops
Drug (on hand) / Fluid per min.
Slide 15 : Desired dose X Weight X Drop set
----------------------------------------------------------------- = drops
Drug (on hand) / Fluid per min. Here’s another:
You are ordered to give a Procainamide infusion at 4 mg per minute. You have a 60 drop set, 2 grams of Procainamide, and a 500cc bag of D5W. How many drops per minute? Plug the numbers into the formula below:
4 X 60 (leave out the weight for Procainamide) = 240
----------------------------------------------
2000 mg divided by 500cc = 4
240 divided by 4 = 60 drops per minute.
Slide 16 : Desired dose X 90kg X 60 Drop set
----------------------------------------------------------------- = drops
200000mcg (on hand) / 500 (fluid) per min. Here’s another:
You are ordered to give a Dopamine infusion at 5 mcg/kg/per minute. You have a 60 drop set, 200 mg of Dopamine, and a 500cc bag of D5W. Your patient weighs 90 kg. How many drops per minute? Plug the numbers into the formula below:
4 X 90 X60 = 21600
----------------------------------------------
200000 mcg divided by 500cc = 800
21600 div. by 800 = 27 drops per min.
Slide 17 : Desired dose X Weight X Drop set
----------------------------------------------------------------- = drops
Drug (on hand) / Fluid per min. You are ordered to give an Epinephrine infusion at 5 mcg/per minute. You have a 60 drop set, 1 mg of Epinephrine, and a 250cc bag of D5W. How many drops per minute? Plug the numbers into the formula below:
5 X (no weight needed) X60 = 300
----------------------------------------------
1 mg divided by 250cc = 4
300 div. by 4 = 75 drops per min.
Slide 18 : You are ordered to give an Epinephrine infusion at 8 mcg/per minute – THROUGH A SYRINGE PUMP. You have a 60 drop set, 1 mg of Epinephrine, and a 250cc bag of D5W. How many drops per minute? Plug the numbers into the formula below – THE SYRINGE PUMP WANTS CC’S PER HOUR. Remember, with some pumps, there is no need to calculate a drop set factor:
5 X (no weight needed) X (no drop set needed)= 5
--------------------------------------------------------
1 mg divided by 250cc = 4
5 div. by 4 = 1.25 CC’s per min.
1.25 cc’s per min. times 60 min = 75 cc/hr
Slide 19 : Now, prepare to work out some problems on your own.
Take out a sheet of paper. After the first few problems, you will be timed. You will have 30 seconds to achieve the correct answer, to within 4 drops per minute, or 0.1 cc per minute. (If you are 0.1 high, you will give an extra 6cc per hour).