The Nursing Math Thread

Thanks a bunch! :)

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.

Answer: Add 265.5 mL of water to the can.

Hope this helps!

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?

#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

Answer: 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

Answer: 10 mcg/min.

Hope this helps! :)

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!

Thank you both your reply's , they where very helpfull.

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

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.

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..

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.

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?

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

any opinions on whether or not i should take clinical calculations (on-line) as a pre-nursing student to prepare for the nursing program starting in aug? i am thinking i will not learn much with it being an on-line course and that is the reason for taking it ahead of time. should i just teach myself?