# Math Again

Posted
by RNrerun (New)

I'm doing some practice problems, and this is from nursesaregreat.com:

A procainamide drip is ordered (2 gm in 250 cc of D5W) to infuse at 4mg/kg/min. The patient weighs 165 lbs. Calculate the drip rate in cc/hr for which the infusion pump will be set at.

165 lbs = 75 kg

2gm = 200,000 mcg

4mg = .004 mcg

I'm trying to do the formula like this:

solution cc

__________ X 60min/hr X kg X mcg/kg/min = cc/hr

drug mcg

Am I doing this right? The answer should be 30, but that's not what I'm getting. I'm sort of hoping this problem has a mistake in it because it has fried my brain! I did, however, catch the preposition at the end of the sentence, so maybe I should have majored in English.

I have tried it a few different ways and keep getting 2250/hr.

250cc/2g x 4mg/kg/min x kg/2.2lbs x g/1000mg x 60min/hr= 2250cc/hr

Edited by Asmorris
error

Specializes in community small-town med/icu unit. Has 2+ years experience.

4mg = .004 mcg

is wrong.

4 MILIgrams (mg) = 4000 MICROgrams (mcg)

And.. why are you working it down to mcg when the question is asking for mg/kg/min?

Is it really suggesting you run it at 4mg/kg/min (which is a very HIGH dose) or did you have a typo there?

When you break down numbers/values to smaller-than-required values, you introduce a greater risk of decimal place errors.

Edited by jmdRN

2.25cc/hr if it was supposed to be 4 mcg instead of 4 mg

Edited by Asmorris
error

Specializes in Infusion. Has 5 years experience.

I keep getting 2250 cc/hr.

300 mg/min (amt needed)

______________________ X 250 cc = 3.75 cc/min X 60 = 2250 cc/hr

2000 mg (amt you have)

By the way, 2 grams = 2,000,000 mcg.

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma. Has 41 years experience.

Procainamide is administered intravenously or orally. When administered intravenously, a loading dose should first be given, though care should be taken not to cause hypotension. Procainamide's major active metabolite is N-acetyl procainamide (NAPA), which is approximately equipotent with the parent drug as an antiarrhythmic agent. NAPA has an elimination half-life about twice that of procainamide, and it can reach somewhat higher plasma levels during chronic procainamide administration. Loading dose is 100 mg IV bolus given slowly over 5 minutes. Max dose is 17 mg/kg. Use is discontinued when dysrhythmia is suppressed, or if hypotension ensues, QRS complex widens by 50% or more, or maximum dose is achieved.

Now the math.....you will find these very valuable

DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

http://www.davesems.com/files/drug_dose_calculations.pdf

Specializes in Infusion. Has 5 years experience.

I like dosagehelp.com. Simplifies the questions. Like jmdRN says don't "over" convert your grams and milligrams. If you have a problem with both mg and gm, just convert one to the other. When you are taking a test, make sure that you remember which is a larger mass. If you have 1 gram of something, it's going to be 1,000,000 mcg. I think you found a problem with a typo.

Specializes in Pedi. Has 14 years experience.

Well, in your problem, you say the dose is in mg/kg/min and then you're trying to work out the answer in mcg/kg/min. So there's problem #1. 4 mg/kg/min seems like an extremely high dose of procainamide... 300 mg/min? Seems unlikely.

Wow. Thanks for all the help. I'm going to assume there's something wrong with this problem. I'm trying to re-learn all these calculations that I haven't done in years and years, and it doesn't take much to confuse me. I have been using dosagehelp.com to practice, and I'll check out the other one that Esmel reccommended. I'll have to take a medications test at the hospital, and I'm trying to get all this straight in my head before I go in there!

Thanks!

Good luck on the test!

Wow. Thanks for all the help. I'm going to assume there's something wrong with this problem. I'm trying to re-learn all these calculations that I haven't done in years and years, and it doesn't take much to confuse me. I have been using dosagehelp.com to practice, and I'll check out the other one that Esmel reccommended. I'll have to take a medications test at the hospital, and I'm trying to get all this straight in my head before I go in there!

Thanks!

There's nothing wrong with the problem.

In this case, the patient's weight is irrelevant - it doesn't impact the dose, so it's simply left out.

dose ordered = 2 g in 250 cc (cc = mL)

infusion rate = 4mg/min

4mg/min x 250mL/2g x 1g/1000mg x 60min/hr = 30 mL/hr

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma. Has 41 years experience.

There's nothing wrong with the problem.

In this case, the patient's weight is irrelevant - it doesn't impact the dose, so it's simply left out.

dose ordered = 2 g in 250 cc (cc = mL)

infusion rate = 4mg/min

4mg/min x 250mL/2g x 1g/1000mg x 60min/hr = 30 mL/hr

The thread is over a year old....and I beg to differ.......the weight IS relevant.....

A procainamide drip is ordered (2 gm in 250 cc of D5W) to infuse at 4mg/kg/min. The patient weighs 165 lbs. Calculate the drip rate in cc/hr for which the infusion pump will be set at.

This math question is all about the weight.