Math Quiz I Need Help....levophed

Nurses General Nursing

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I am up against a wall. I have a cheat sheet for figuring out the pump rate for Norepinephrine (Levophed) per hour for the doc's order mcg/min. but can't set up the formula to make sure the cheat sheet is correct.

For example, let's say it comes in a concentration of 4mg/250 ml of D5W which divided = 16mcg/ml (I know I convert the 4mg into mcg. = 4000mcg divided by 250).

Now, if the doc orders 3mcg/min my cheat sheet says the pump rate per ml/hr is 11.25, so I set the pump at 11.25 cc BUT can anyone tell my fried brain how to set up this formula to double check and I understand? I have notes all over the place but this simple one escapes me and its important for all of us to make logical sense out of what we are doing : ) Thanks, Kitty. **** Please set up the whole formula for all you math folks & is there a web site for quick solutions to us that are not so math inclined?

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Specializes in Assisted Living Nurse Manager.

I will try my hand at this, lets see what everyone else thinks!

order 3mcg/min

On hand 16mcg/ml

3mcg/16mcg = 0.18 = 0.2ml/min

0.2ml/min x 60min = 12ml/hr

This is how my brain figures it:)

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Now, if the doc orders 3mcg/min my cheat sheet says the pump rate per ml/hr is 11.25, so I set the pump at 11.25 cc BUT can anyone tell my fried brain how to set up this formula to double check and I understand?

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Here is the formula:

ML/Hr x 250ml/4mg (on hand) x 1mg/1000mcg (conversion) x 3mcg/min (ordered) x 60min/HR = 45000/4000 = 11.25 ml/hr ...now if you can set your pump for that exact amount great! if not you have to round up or down.

Yes there is a good link for some calcs..and a key with answers:

http://home.sc.rr.com/nurdosagecal/quiz_3.htm some of these are dimensional analysis for health ...if you get to know the formulas it's easy/helpful...but there are a few of them :) Practice makes perfect. :blushkiss :monkeydance: :nurse:

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Dear Happy Grad,

Thanks for your input, but I cannot figure how you got the 45,000. You have the correct answer and I understand how you got the 4000 mcg. Can you break it down just a bit clearer, my brain is going down, down, down but I am stubborn and can't let it rest.

Thanks, Kit

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Furoffire,

Although there is nothing wrong with performing all steps consecutively as explained by happygrad06, I personally find that if I try this method I am much more likely to make a math/calculation error. For this reason, I would do this problem in 4 separate steps as follows.

1. Determine the per mL concentration of Norepinephrine if this information was not contained on the container. (4 mg / 250 mL = 0.016 mg/mL)

2. Since the order was given as mcg/minute, next convert the concentration to mcg/mL.

3. Determine the total amount of medication to be infused in 1 hour by multiplying the dose by 60. (3 mcg x 60 min = 180 mg/hour)

4. Determine the infusion rate by dividing the total hourly dose by the supplied concentration. (180 mcg/hour / 16 mcg/mL = 11.25 mL/hour)

Hope that this helps.

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Furoffire,

Although there is nothing wrong with performing all steps consecutively as explained by happygrad06, I personally find that if I try this method I am much more likely to make a math/calculation error. For this reason, I would do this problem in 4 separate steps as follows.

1. Determine the per mL concentration of Norepinephrine if this information was not contained on the container. (4 mg / 250 mL = 0.016 mg/mL)

2. Since the order was given as mcg/minute, next convert the concentration to mcg/mL.

3. Determine the total amount of medication to be infused in 1 hour by multiplying the dose by 60. (3 mcg x 60 min = 180 mg/hour)

4. Determine the infusion rate by dividing the total hourly dose by the supplied concentration. (180 mcg/hour / 16 mcg/mL = 11.25 mL/hour)

Hope that this helps.

I'm in agreement here as well! Even more understandable to my mind is working the formula this way:

3mcg per min. ordered X 60 minutes in one hr. = 180 mcg per hr.

180 mcg / ? ml. per hr. = 16 mcg / 1 ml. per hr.

To solve for ? I cross multiply and then divide.

(180 mcg per hr. X 1 ml.) divided by 16 = 180 divided by 16 = 11.25 ml./hr.

So with this concentration, 11.25 ml./hr. = 180 mcg per hr.

To check divide 180 mcg in one hr. by 60 min. in one hr. 180 divide by 60 is 3 mcg/min. Voila...you've returned to the original order.

I'm one of those that has to do every step....I know, I know...anal retentive.:rolleyes:

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:uhoh21: Holy crap... Are you kidding me???? And I thought I was good at math! I guess this is what I have to look forward to huh??? :lol_hitti

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Got it, finally. Thank you. Now for another hurdle, DILTIAZEM/

CARDIZEM. I see that the gtt is 1:1 but the bolus is blowing my mind a bit.

Lets say you mix the 125mg into 125 D5 or NS (I guess its in 25cc and you add to the piggy back of 100 that = 125cc.

The bolus is 0.25mg/kg undiluted over 2 minutes. Lets say the patient is 70kg. I know you .025mg X 70kg = 17.50 mg? Do you IVP the 17.50 over 2 minutes? The Tired Kat

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Dear Happy Grad,

Thanks for your input, but I cannot figure how you got the 45,000. You have the correct answer and I understand how you got the 4000 mcg. Can you break it down just a bit clearer, my brain is going down, down, down but I am stubborn and can't let it rest.

Thanks, Kit

Sure kit. The 45000 comes from just multiplying across the top of the bar all the number (same as you multiply across the bottom of the bar to get 4000). This is dimensional analysis..you can get a really simple book with a great step by step CD in it online at a bookstore..just type in dimensional analysis for healthcare/meds... it'll pop up..it has a blue cover.

The thing that simplifies this type of thing is that it's calculations..you just do the calc for whatever you need to get. Same every time ... and out of all the math tests we took...and we took them every quarter I never missed once. You have to be able to grasp calculation formulas though - formulas are basic, but you have to be able to set them up if that makes sense..the book really simplifies them :) Anyway, there is more than one way to get your answer, I use formulas as they are simple. But you can do more complex thinking..I tend to get more confused that way! All the formula is...is taking what you have onhand... doing the conversion..and timsing it by what you want... and that is about it. You just cross cancel your labels (i.e. mg) and that leaves your numbers... and your ml/hr label of course..the you just deal with the numbers...which you just

multiply straight across and then divide your end answer.

Hope that helps but the CD really works wonders. Also take a look at the link I sent, it shows you how to break them down too but not as good as the books out there that have CDs.

I used to think I wasn't good at math but these aren't that complicated once ya get the hang of em.

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Specializes in Utilization Management.
Got it, finally. Thank you. Now for another hurdle, DILTIAZEM/

CARDIZEM. I see that the gtt is 1:1 but the bolus is blowing my mind a bit.

Lets say you mix the 125mg into 125 D5 or NS (I guess its in 25cc and you add to the piggy back of 100 that = 125cc.

The bolus is 0.25mg/kg undiluted over 2 minutes. Lets say the patient is 70kg. I know you .025mg X 70kg = 17.50 mg? Do you IVP the 17.50 over 2 minutes? The Tired Kat

What confuses me is the "undiluted" part. It's already been diluted in the piggyback bag of 100 ml. So let's just say that you don't need to dilute the mix any further, shall we? and yes, you push that over 17.5 mg over 2 minutes.

Here's the link:

http://www.fda.gov/medwatch/SAFETY/2004/dec_PI/Cardizem Injectable-Lyo-Ject.pdf#search='cardizem%20bolus%20iv'

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I'm in agreement here as well! Even more understandable to my mind is working the formula this way:

3mcg per min. ordered X 60 minutes in one hr. = 180 mcg per hr.

180 mcg / ? ml. per hr. = 16 mcg / 1 ml. per hr.

To solve for ? I cross multiply and then divide.

(180 mcg per hr. X 1 ml.) divided by 16 = 180 divided by 16 = 11.25 ml./hr.

So with this concentration, 11.25 ml./hr. = 180 mcg per hr.

To check divide 180 mcg in one hr. by 60 min. in one hr. 180 divide by 60 is 3 mcg/min. Voila...you've returned to the original order.

one of those that has to do every step....I know, I know...anal retentive.:rolleyes:

PERFECT!

you've got it!:yeah: :yeah:

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Dear Happy Grad,

I will check out that book, its on the web site you referred? I am trying to get a grip on all this and make notes. On the job when a patient goes sour I don't feel like I have the time to do work on math check out references etc. So I feel I need to get a grip, understand what I am doing and do it fast!!! With the pressure on the job and sometimes lack of support can be scarry. But I am new to this and what can one expect? Looking forward to the day where this can all be done in my sleep :-), anyway I will do some searching on Amazon and see what is available, they do quick delivery and are great.

Thanks to all of U!!!!! Kitty

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