# The Nursing Math Thread - page 23

A member pm'd me the following question highlighted below. We created this thread for you guys to talk about math, solve math problems, and post math websites that you have found helpful. I was... Read More

1. Hello! I hope I am posting this question in the right area:

I'm working on a math sheet to challenge a nursing calculation course at my college. I answered most of the questions okay, but there were a few I'm confused about:

1. Calculate the drip rate for 500 cc of IV fluid to be given by microdrip over an 8 hour period.
Wouldn't that be 63ml/hr? My answer key said 63gtt/min (I thought it would be ml/hr, not gtt/min). But in order to get the gtt/min, wouldn't I need to know the IV set first?

2. At 8am, an IV is infusing 35gtt/min and there is 750 LIB. DF 12. What time will the IV finish?
Not sure how to set this one up. Also, I've never seen the abbreviation LIB before. Is it suppose to be AD LIB?

3. A patient is to receive a 40% solution of Osmolyte-HN by PEG tube. How many mL of water must be added to a 6oz can of Osmolyte-HN to administer this feeding?
Also unsure how to set this one up

Any help would be greatly appreciated.
2. Quote from summer-dreamer
Hello! I hope I am posting this question in the right area:

I'm working on a math sheet to challenge a nursing calculation course at my college. I answered most of the questions okay, but there were a few I'm confused about:

1. Calculate the drip rate for 500 cc of IV fluid to be given by microdrip over an 8 hour period.
Wouldn't that be 63ml/hr? My answer key said 63gtt/min (I thought it would be ml/hr, not gtt/min). But in order to get the gtt/min, wouldn't I need to know the IV set first?

2. At 8am, an IV is infusing 35gtt/min and there is 750 LIB. DF 12. What time will the IV finish?
Not sure how to set this one up. Also, I've never seen the abbreviation LIB before. Is it suppose to be AD LIB?

3. A patient is to receive a 40% solution of Osmolyte-HN by PEG tube. How many mL of water must be added to a 6oz can of Osmolyte-HN to administer this feeding?
Also unsure how to set this one up

Any help would be greatly appreciated.

1. Microdrip is 60 gtt/ml

2. LIB is left in bag. So the question is asking how long will it take for 750 ml to be done when there is a drip factor of 35 gtt/ml

3. Im not sure. This is how I would set it up. Your patient cannot tolerate full strength feedings so its 40 percent. You are giving 6 oz of feeding.

x= total amount of feeding

6 oz = .40 (x)
x=15

15 (total amount for feeding) - 6 oz ( amount of tube feed)= 9 oz of water
3. Thanks a bunch!
4. Quote from summer-dreamer
Hello! I hope I am posting this question in the right area:
1. Calculate the drip rate for 500 cc of IV fluid to be given by microdrip over an 8 hour period.
Wouldn't that be 63ml/hr? My answer key said 63gtt/min (I thought it would be ml/hr, not gtt/min). But in order to get the gtt/min, wouldn't I need to know the IV set first?

You're partially right; the infusion rate is 63 mL/hr, which on microdrop tubing would be 63 gtt/min. This is what's so handy about microdrop tubing - it's always 60 gtts/min, which directly equates to mL/hr.

2. At 8am, an IV is infusing 35gtt/min and there is 750 LIB. DF 12. What time will the IV finish?
Not sure how to set this one up. Also, I've never seen the abbreviation LIB before. Is it suppose to be AD LIB?

Use your same drip-rate formula and plug in the numbers you know. In this case, you know VTBI, drop factor and drip rate; entering those values gives you

(750 mL * 12 gtt/mL) / X min = 35 gtt/min

Solve for X:
Multiply 750 x 12. 9062.5 / X = 35
Multiply both sides by X to clear the divisor. 9062.5 = 35X
Divide both sides by 35 to get X by itself. 258.9 = X

Answer: 260 minutes, or 4 hours 20 minutes. Starting at 0800, this infusion will be done at 1220.

3. A patient is to receive a 40% solution of Osmolyte-HN by PEG tube. How many mL of water must be added to a 6oz can of Osmolyte-HN to administer this feeding?
Also unsure how to set this one up

This one's a basic volume ratio: V1 * C1 = V2 * C2, where V1 and C1 are your starting volume and concentration, and V2 and C2 are your desired volume and concentration. However, we're supposed to be dealing in metric values here, so we've got to get that can volume out of customary units first.

1 US fluid ounce = 29.5 mL
6 oz = 177 mL

Now, we plug in the numbers and solve for V2:

177 * 1 = V2 * .4

Multiply 177 x 1. 177 = V2 * .4
Divide both sides by .4 to get V2 by itself. 442.5 = V2

Total volume of the feed is 442.5 mL, from which we subtract our starting volume of 177 mL to get the diluent volume.

Hope this helps!
5. I have a couple math prob I seem to be having a hard time figuring the formula.

#1. Order: Lidocaine 2mg / min. on hand: Lidocaine 2g / 500 ml. what rate will you set the pump?

#2. Nitroglycerine 50 mg in 250 ml d5w is infusing at 3 ml / hr. How many micrograms per minute is pt receiving?
6. #1: This one's a three-step problem: you're given a solution (2 g/500 mL) and a dose (2 mg/min), and you need to figure out an infusion rate (note, NOT a drip rate - this med is going on pump!) So, you need to calculate how many mg per mL (the concentration) of your solution, calculate how many mg you're ordered to deliver per hour (hourly dose), and then calculate how many mL per hour you need to program into the pump (rate). Thus:

a) Convert g to mg and divide by volume in mL to get concentration. 2 g/500 mL = 2000 mg/500 mL = 4 mg/mL
b) Multiply minute dose by 60 to get hourly dose. 2 mg/min x 60 min = 120 mg/hr
c) Divide hourly dose by concentration to get rate. 120 mg/hr / 4 mg/mL = 30 mL/hr

#2: I smiled when I saw this problem; we hang that same concentration of NTG multiple times on every single shift, so we all have the conversions memorized. However, the setup for this problem is almost the same as the previous. You still need concentration, dose and rate; the only differences are that you're given the rate and you need to calculate the dose, and that dose needs to be in mcg instead of mg (1 mg = 1000 mcg). Otherwise, same problem. Thus:

a) Convert mg to mcg and divide by volume to get concentration. 50 mg/250 mL = 50000 mcg/250 mL = 200 mcg/mL
b) Multiply rate by concentration to get hourly dose. 3 mL/hr x 200 mcg/mL = 600 mcg/hr
c) Divide hourly dose by 60 to get minute dose. 600 mcg/hr / 60 min = 10 mcg/min

Hope this helps!
7. Quote from cdk001
I have a couple math prob I seem to be having a hard time figuring the formula.

#1. Order: Lidocaine 2mg / min. on hand: Lidocaine 2g / 500 ml. what rate will you set the pump?

#2. Nitroglycerine 50 mg in 250 ml d5w is infusing at 3 ml / hr. How many micrograms per minute is pt receiving?

Without trying to confuse you too much, allow me to suggest a fantastic method to solving multiple-step problems.

The cure: Dimensional analysis!

You'll see it in chemistry and especially dosage problems.

#2. Notice: 50mg in 250ml means 50mg/250ml and so on... You based the ratio based on final answer needed. If you needed to know ml/hr then you would have ml on top ... 250ml / 50mg and so on. On to the problem!

NEEDED: mcg/mn

Here are the clues: 50mg/250ml, 3ml/ hr

Conversions: 1000 mcg in 1mg or 1000 mcg/1mg, 1hr/60mn (note that I set it up based on how I want the final answer to be)

Here we go in one step:

50 mg/250ml * 3 ml/hr * 1000mcg/1mg *1hr/60mn = 10 mcg/mn (Note that the other terms cancel)

Hope this is an extra tool in your problem solving!
9. Is there a dimensional analysis way to do the math problems

1) 50 mg in 250 ml infusing at 25ml / hr whats the mg per hour

2) 25,000 units in 250 ml infusing at 30 ml /hr how many units per hr
10. Quote from cdk001
Is there a dimensional analysis way to do the math problems

1) 50 mg in 250 ml infusing at 25ml / hr whats the mg per hour

2) 25,000 units in 250 ml infusing at 30 ml /hr how many units per hr

I'll be willing to help if I can see your thought process based on the info given above.
11. Quote from CareRx
I'll be willing to help if I can see your thought process based on the info given above.

I do 25,000\250 gives me 100 and then I take 100x30ml\hr gives me 3000 units per hour,

but when I do dimensional analysis 25,000 u\250ml x 30ml\1hr x 1hr\60 gives me 50 it's the same with the other question I cant seem to figure out where to put the hr\min.

I understand the question askes for ml\hr or units\hr you set up the question first that way..
12. Quote from cdk001
I do 25,000\250 gives me 100 and then I take 100x30ml\hr gives me 3000 units per hour,

but when I do dimensional analysis 25,000 u\250ml x 30ml\1hr x 1hr\60 gives me 50 it's the same with the other question I cant seem to figure out where to put the hr\min.

I understand the question askes for ml\hr or units\hr you set up the question first that way..
You set up the problem right. Here you don't worry about minutes because you are ask the answers in mg/hr or ml/hr respectively.

Quote from cdk001
Is there a dimensional analysis way to do the math problems

1) 50 mg in 250 ml infusing at 25ml / hr whats the mg per hour

50 mg/250ml x 25ml/hr = 5mg/hr

2) 25,000 units in 250 ml infusing at 30 ml /hr how many units per hr
25,000 units / 250ml x 30 ml / hr = 3000 units / hr

If the question wanted to know in #2 how many units per mn?

25,000 / 250 ml x 30 ml / hr x 1 hr/60mn = 50 units / mn

(which makes sense, you wouldn't want 3000 units per mn; and in the question below, you should expect the answer to be much less as well)

(note that you can skip a step and add 60 mn right away under 30ml, but perhaps it is best when you are a just a little bit advance to do it.)

#2: 25,000 units in 250 ml infusing at 30 ml /hr, how many units per second?
13. Quote from CareRx
You set up the problem right. Here you don't worry about minutes because you are ask the answers in mg/hr or ml/hr respectively.

25,000 units / 250ml x 30 ml / hr = 3000 units / hr

If the question wanted to know in #2 how many units per mn?

25,000 / 250 ml x 30 ml / hr x 1 hr/60mn = 50 units / mn

(which makes sense, you wouldn't want 3000 units per mn; and in the question below, you should expect the answer to be much less as well)

(note that you can skip a step and add 60 mn right away under 30ml, but perhaps it is best when you are a just a little bit advance to do it.)

#2: 25,000 units in 250 ml infusing at 30 ml /hr, how many units per second?

I did this 25,000 / 250 x 30 ml / 1 hr x 1hr / 60 mn x 1mn / 60 sec = 0.83333 rounded to 1 unit/sec is that right? or did I mess it some how