Ahh pharm calc!!

Examples:

1. The physician orders 1000 mL of D5W to be administered over 6 hours. What would you set the IV pump at to administer this dose of fluid to your patient?

2. The physician orders 2 units of insulin IV every hour. The pharmacy sends a 100 mL bag of NS with 50 units of insulin added to it. What would you set the IV pump at to deliver 2 units of insulin every hour to your patient?

3. The patient has an IV pump infusing at 15 mL/hr. The bag infusing states 250 mL of NS with 100 units of insulin added. What dosage of insulin is this patient receiving?

Answers:

1.

1000 mL/6 hours =

167 mL/hr

2.

2 units/hr x 100 mL/50 units =

2 x 100 mL/50 hr =

200 mL/50 hr =

4 mL/hr

3.

50 mL/hr x 100 units/250 mL =

5000 units/250 hr =

20 units/hr

I use dimensional analysis... it's the best way to come up with the right answer (imo). If you need help with dimensional analysis, Khanacademy.com is a really good website (for just about everything).

Another thing you might find helpful before you even start doing calculations is to look at what you know already.

For #3, you know you have 100 units in 250cc. So you know that there is (more than or less than) one unit per cc?

Right, it has to be less than one unit per cc. If there were 250 units in 250 cc, that would be 1 unit per cc, and there's less. A bunch less, actually.

So if you're giving 15cc /hour of that, then are you giving (more than or less than) 15 units? Right, less than, has to be. So even before you start you know that whatever the exact answer is, it's gotta be less than 15 units. So when you get an answer that's bigger than that, you know it has to be wrong.

So when you know you have 100 units in 250 cc, how many units are there in 1 cc?

So how many units are being given in 15cc?

For people who find dimensional analysis confusing , largely because there's too much going on to take in all at once, breaking things down into more parts is easier to follow.

Thank you it's just a lot formulation memorization math is not my strong suit those websites helped a lot I really didn't think in the real world that they used a lot of the calculations but I was talking to a nurse I work with at the hospital and she said they use it all the time and I better learn it so thank you

Um, how did you think patients got the right doses of things? Why do you think that your school emphasizes med math? I can promise you it's not just to annoy the students! :)

This is a great site....DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

number one is correct. umber 2 is correct....number 3 WATCH YOUR CONVERSIONS

you need to calculate how many units of insulin are per ml of fluid. If there is only 100 units in the whole 250ml's how can you have 5,000 units infusing at 250ml/hr

So if you have 100units in 250mls of fluid....you have how many units are per ml of fluid?

100units/250mls = ? units/ml so you have 0.4units of insulin/ml of fluid if that fluid is infusing at 15ml/hr how many units per hour is that??

0.4u/ml x 15ml/hr = ?? units per hour......

I MEANT to do that! See if anyone was paying attention...

Actually, I now see what I actually did wrong... I knew I was wrong, I just couldn't see it. I put 50 in the place where 15 should have been... WHOOPS! And that is why you triple check and get a second nurse to check insulin...

15 mL/hr x 100 units/250 mL =

1500 units/250 hrs =

6 units/hour

Actually, there are a good many drugs that can have worse effects if OD'd or underdosed than insulin, and a lot harder to fix. I really don't understand why people get so fluffed about insulin but nobody has an ironclad policy about checking, say, IV digoxin.