Med Math Question

Hey everyone I have a Med Math Exam today but this NG fluid replacement for pediatrics is throwing me off. I understand the first two parts of the problem but can someone please help me with the last two
2a. The order is for 500 mL D5/0.225% NS @ 63 mL/hr. The NG drainage is to be measured and replaced with the primary IV solution q.4h. Maximum hourly IV rate is not to exceed 85 mL/hr. What is the rate of the primary IV?
Ans: 63 mL/hr (I understand this)
2b. The nurse can increase the IV by how many additional mL/hr during the replacement of the NG drainage of?
Ans: 22 mL/hr (I understand this because the maximum rate cannot exceed 85 mL/hr so there it can be increased to 22 mL/hr to reach this maximum from 63 mL/hr)
2c. The child's NG tube drains 66 mL. What is the infusion time of the replacement IV fluid?
I do not understand how to work this problem I do understand Infusion Time (IT) = Total amount of IV fluid (mL)/ Hourly rate (mL/hr). I do not know what numbers to use
2d. The fluid replacement is started at 12 noon. What is the completion time?
Once I find the infusion time I can do the completion time. Because I am unable to do the first step to get to this step I am stuck. 
About Nscorpiored
Joined: Apr '09; Posts: 108; Likes: 23
Patient Service Associate; from US
Specialty: None still a student 

Aug 30, '12LOL I am answering my own question I had a friend just explain it to me
So I will answer if someone needs help
2c. You take the drainage and divide it by the replacement...take that number and convert it to hours and minutes (66 mL/ 22 mL/hr = 3 to hours is simply 3 hours)
2d. You then take your infusion time (3 hrs) and add this to your original time and this will give the completion time 

Aug 30, '12This scares me lol I just started nursing school today and ordered my med math book. So i'm currently waiting for it to arrive. In the mean time I am trying to find practice problems online on converting the basics like cm to m in the metric system. However, when I read the problem you just posted I begin to freak out lol I have no idea how to solve that. But I want to be ahead of the game before my math exam comes around. Any advice??

Aug 31, '12If you go back and read through it actually isn't as bad as you would think. I was also scared when I took my first med math exam. To be honest I failed the first 1 but my school allows us to take at least up to 3 tries. On the third try it could result in you being put out the program. It is hard sometimes to remember all the math, especially for intake and output and conversions at time.
But taking the problem step by step. I got the numbers from one comparing the primary IV rate with the IV rate maximum. You can only go up to 85 mL/hr from the original 63 mL/hr, meaning you can increase your rate up to 22 mL/hr (this is your replacement.
You then have drainage of 66 mL. In order for you to get your infusion time you must take your drainage and divide it by your replacement. In other words 66 mL divided by 22 mL/hr this will give you 3 hours.
Looking back at your problem it states it was started at 12 (noon) what would be your completion time. Well you take your 3 hour add that to 1200 and you will get 1500 (written in military time) and this will translate into 3:00 pm
Make sense 
Aug 31, '12I think that you are reading this problem incorrectly, Regardless, this does highlight the need to clarify orders with the ordering physician.
You have an order limiting the maximum infusion rate to 85 mL/hour. Your maintenance fluid is currently infusing at 63 mL/hour. This means that you can increase the infusion rate by 22 mL/hour, not that you have to increase the rate by 23 mL/hour.
You have an order to measure and replace NG output every 4 hours. At my facility, output replacement is infused over the same time period that it was collected. Therefore, the 66 mL NG output would be replaced over 4 hours, at 16.5 mL/hour. To infuse over 4 hours, the infusion rate would be increased to 79.5 mL/hour, with an infusion completion time of 1600.
the same time period that it wascollected. Therefore, the 66 mL NGoutput would be replaced over 4 hours, at 16.5 mL/hour. To infuse over 4 hours, the infusion ratewould be increased to 79.5 mL/hour, with an infusion completion time of 1600 
Sep 1, '12Because you are using your facilities standards it will come out differently. I was taught to take replacement, what you can increase it to, and divide that into NG drainageNot the way you are doing it but thank you since there are variations