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Help Desk for Nursing Students Need help with your homework? Here's the place!

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Old 10-28-2015, 11:50 AM
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Default Dosing questions making you dizzy?

http://www.dosagehelp.com/

This is a great website for helping students understand how to work with medication and fluids dosing questions...not just to get the right answer, but to understand why. There are practice questions with answers and rationales, too. You can never practice this too much!

If you want to run your questions by us here, we're all ears!
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Old 11-08-2015, 10:56 PM
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The best advice I can give for med math is to always start your dimensional analysis with the unit you're looking for on the top of your fraction. Then cancel out the units on the bottom until you're left with exactly what you need.

For example: The doctor prescribes 1.2 grams Cefazolin. Cefazolin comes in 2 grams per 500 mL. The infusion should run over 30 minutes. How many mL per hour do you set the pump for this dose?

So, you need to find how many mL per hour for this dose (mL/hour). Start off your fraction with the unit that gives you mL on top (500 mL has 2 grams of Cefazolin)

(500 mL/2 grams) x (1.2 gram/dose) x (1 dose/30 min) x (60 min/1 hour)

When you cancel out all your units, you're left with mL/hour. In this case, the pump would be set to 600 mL per hour.

This will administer the necessary 300 mL in 30 minutes, which equals the prescribed 1.2 grams of Cefazolin.

When you start with the unit you need on top first and then cancel out until you have what you need on bottom, you can never go wrong. Where I see students make med math errors, they typically don't follow a consistent method to solve their problems.

(P.S. I realize in the real world, you're going to make darn sure that you only have 300 mL in the bag [or program the pump that only 300 mL will be delivered], so you don't end up administering the full 2 g. I was just trying to come up with an example off the top of my head)
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Old 12-15-2015, 10:08 PM
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How do you know how to set up your equations for med math problems?

It's so important to read the question twice to be sure you know what they're testing you on. Here's a classic example:

Your physician's prescription is for miraclecillin. You have a vial to reconstitute to draw up the IM dose. The label says, "Miraclecillin 5,000,000 units. Add 3.4ml of sterile water for a final concentration of 1,000,000 units/ml." Give 250,000 units IM. How many ml do you inject?

Now, you can pull out your dimensional analysis equation and stare at it, trying to remember how to put in all those numbers so you draw up the correct dose. You can make yourself crazy when you get weird answers, but don't just do something, stand there. Stop. Did you do what I told you and read it twice before doing anything? No, I didn't think so.

What's important here?

Right. Once you have followed the directions on the vial to add 3.4ml of diluent, you have in your hand a solution that's one million units per ml. If you know that 250,000 is one quarter of one million, then you can do this one in your head: the answer is one quarter ml, 0.25ml.

Many med math questions are like that, filled with extraneous information. They aren't really testing you to see if you can divide 250,000 / 1,000,000. They're testing you to see if you can read and problem-solve, to know what's really being asked.

What's your last med math puzzler?


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Old 12-16-2015, 03:33 AM
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I almost looked up miraclecillin. Too funny!

My favorite Med math formula is d/h x v.

Works like a charm on 90% of Med math problems. The other 10% are weight based or drip rate problems.

So, what does this formula mean?

D = desired dose (what your order says to give the patient)
H = what you have on hand (the formulation you have available from pharmacy)
V = volume (how much did the pharmacy give you)

For example, your order reads gabapentin 600mg PO TID. Your pharmacy sneds you a bottle of capsules. The label reads gabapentin 200mg capsules, qty. 90. What do you give your patient?

Desired = 600mg, on hand = 200mg, volume = 1 capsule
600/200 x 1 = 3 capsules!

Double check by multiplying your answer and your on hand, then dividing by your volume, to make sure it matches your order. Does it make sense? If you give your patient 3 capsules of 200 mg, does that equal your order of 600 mg? 3x200=600! Success!

Works on IV push, too.

Order: 0.5mg Ativan IV push TID PRN anxiety. The pharmacy sends you a vial of 1mg/1ml.

Desired 0.5mg, on hand 1mg, volume 1ml ---> 0.5x1x1 = 0.5 ml!!
Double check: 0.5 x 1 = 0.5 Success! (save yourself a step if your volume is 1 and skip dividing by 1)

And, for a tricky one -

Order: 25 mcg fentanyl IV push Q30 min PRN pain. You get a vial out of the Med machine that reads fentanyl 100 mcg/2ml.

Desired 25 mcg, on hand 100 mcg, volume 2 ml ---> 25mcg/100mcg x 2ml = 0.5ml
Double check: 0.5ml x 100mcg = 50 ml/mcg, 50 ml/mcg divided by 2 ml = 25 mcg Success!
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