# Math calculation. Help!

This is a two-step ml/hr flow rate problem. I need help please.

Medicaton is ordered at the rate of 3mcg/kg/min for an adult weighing 95.9 kg. The solution strength is 400 mg in 250mL D5W. Calculate flow rate to the nearest tenth mL.

Is there a formula that can be applied here.

What have you tried so far?

There was this formula that I saw online (ATI website): (dose/kg/time) (time converted to hourly) (weight in kg)/ (drug concentration per ml)

I started plugging the numbers in according to the formula. (3mcg/kg/min) (95.9 kg)/250 ml. My hunch is I have to multiple 3mcg by 95.9 kg this equals 287.7 kg/mcg then convert to mg.which is 0.287 mg. I converted to mg because the solution is in mg. But my answer is not matching the answer sheet.

How many total mcgs of the drug in 250ml? How many mcgs/ml? And you've got the very first step right (mcgs/kg) but look at the rate.

The total mcg in 250 ml is 250,000mcg. I divided 250/0.001

Try again. You used the volume not the concentration. You cannot convert ml to mcg. You CAN convert mg to mcg. What factor in the question is written in mg and how many mg are there?

Well we have 400 mg if we convert to mcg we have 400,000 mcg

Very good. So we have 400,000 mcg in 250 ml. Using these numbers how would you solve to find out how many mcg are in each ml.

400,000/250=1600

400,000/250=1600

Super. So you know the patient needs 3mcg/kg which totals 287.7 mcg (you figured this out earlier, yay for you) but that's ordered per minute and the pump will be set per hour so with the information you have can you figure out how many ml/hr you need to set the pump. Remember your concentration is 1600mcg/ml.

I solved it and did the the other problems that were similar. 287.7 mcg X 1 MG/400 MG X 250ML/400 MG X 60/1 hour =4315500/400000=10.78

Now, I'm stuck on another problem. lol But thank you for your help with this.

Yay for you sashaq. You're doing a great job. Now you know you can figure it out in mg and then convert to mcg or what I do which is convert first. Both ways are correct and just reflect how our individual brains work. I'm very proud of you for sticking with it. Bring on the next problem.

Edited by Wuzzie

Ok, so far I have solved 18 of my 20 math calculation problems. These 2 are similar.

1. An IV infusion time is 13 hr 20 min. What is its completion time if it was started at 10:45 a.m.?

2. A 20gtt/mL set is used for a restart of 750ml of D5W at 3:03 p.m. at a rate of 32 gtt/min.

Infusion time_________Completion time_____________

I feel like I have done similar problems in the beginning of my program. But now that I'm going into my senior year we are redoing things that we have already been taught. Unfortunately, I seem to have forgotten how to do them.

For the second problem. I did this. 750 X 20gtt/1ml X 32gtt/1 min. I got 15000/32=468.75

I divided 468.75 by 60 minutes to get 7.8125. so 7 hours.

then I got the .81 from 7.8125 and multiplied by 60 minutes. so, .81 X 60= 48.6.

So, my answer was 7 hours and 49 minutes for infusion time. for completion time I just counted from the time started 3:03, which gave me 10:00. then i added my 48 minutes to the 3 minutes and got 51. so 10:51.

I'm sure there are simple steps to solving these problems.

Specializes in Med-Tele; ED; ICU. Has 10 years experience.

2. A 20gtt/mL set is used for a restart of 750ml of D5W at 3:03 p.m. at a rate of 32 gtt/min.

Infusion time_________Completion time_____________

You can come at this in two ways:

1) Think about the volumetric rate (mL/min) rather than the drip rate (gtt/min) and then determine how many minutes it will take to infuse 750mL.

2) Think about how many DROPS that you're going to infuse (that is, how many drops make up that 750mL bag) and then determine how many minutes is will take to infuse that many drops given the specified drip rate.

Either way, your infusion should take 7 hours and 49 minutes

Ok, so far I have solved 18 of my 20 math calculation problems. These 2 are similar.

1. An IV infusion time is 13 hr 20 min. What is its completion time if it was started at 10:45 a.m.?

2. A 20gtt/mL set is used for a restart of 750ml of D5W at 3:03 p.m. at a rate of 32 gtt/min.

Infusion time_________ Completion time_____________

I feel like I have done similar problems in the beginning of my program. But now that I'm going into my senior year we are redoing things that we have already been taught. Unfortunately, I seem to have forgotten how to do them.

For the second problem. I did this. 750 X 20gtt/1ml X 32gtt/1 min. I got 15000/32=468.75

I divided 468.75 by 60 minutes to get 7.8125. so 7 hours.

then I got the .81 from 7.8125 and multiplied by 60 minutes. so, .81 X 60= 48.6.

So, my answer was 7 hours and 49 minutes for infusion time. for completion time I just counted from the time started 3:03, which gave me 10:00. then i added my 48 minutes to the 3 minutes and got 51. so 10:51.

I'm sure there are simple steps to solving these problems.

You got the correct answer, but the equation you wrote does not match the steps you took to get that answer.

You wrote

750mL x 20 gtt/mL x 32gtt/1min

You said that was 750 x 20 = 1500 gtt.

Then you divided by 32. Your equation indicated that you should multiply by 32.

In fact dividing by 32 was the correct step. The correct equation was

750mL x 20 gtt/mL x 1min/32gtt

Specializes in NICU, PICU.

Yay for you sashaq. You're doing a great job. Now you know you can figure it out in mg and then convert to mcg or what I do which is convert first. Both ways are correct and just reflect how our individual brains work. I'm very proud of you for sticking with it. Bring on the next problem.

Wuzzie, that was awesome. In your next life you should be an educator. Or a cheerleader.

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