The Nursing Math Thread

Daytonite, BSN, RN · May 28, 2009

This problem is driving me crazy! I don't even know where to begin in terms of setting it up, etc...
Mr. Angus, age 79, is admitted to the hospital with an exacerbation of Congestive Heart Failure. His main IV order is 1500 ml NS with 20mEq KCl to run over 24 hours. He also has a urinary tract infection and is receiving IV antibiotics 100 ml every 6 hours as treatment. He is currently NPO and ordered a fluid restriction of 1500 ml in 24 hours. How much of his primary IV will Mr. Angus receive if the fluid restriction is enforced?
The correct answer is 1100mL.

Total fluid allowed in 24 hours = 1500 mL

The IV antibiotics are given q6h, or 4 times, in that 24 hour period at 100 mL each time. Each antibiotic infusion contains 100 mL, so 4 x 100 mL each = 400 mL

If only 1500 mL of fluid is allowed in 24 hours and 400 mL of it will be used up giving the antibiotic, that leaves 1500 mL - 400 mL or 1100 mL of the NS with 20 mEq of KCL that can be given in the remaining 24 hours.

olive_nurse · May 28, 2009

Total fluid allowed in 24 hours = 1500 mL
The IV antibiotics are given q6h, or 4 times, in that 24 hour period at 100 mL each time. Each antibiotic infusion contains 100 mL, so 4 x 100 mL each = 400 mL
If only 1500 mL of fluid is allowed in 24 hours and 400 mL of it will be used up giving the antibiotic, that leaves 1500 mL - 400 mL or 1100 mL of the NS with 20 mEq of KCL that can be given in the remaining 24 hours.

That's exactly right. I couldn't have wrote it out better myself! :coollook:

shrimpchips, LPN · May 29, 2009

Total fluid allowed in 24 hours = 1500 mL
The IV antibiotics are given q6h, or 4 times, in that 24 hour period at 100 mL each time. Each antibiotic infusion contains 100 mL, so 4 x 100 mL each = 400 mL
If only 1500 mL of fluid is allowed in 24 hours and 400 mL of it will be used up giving the antibiotic, that leaves 1500 mL - 400 mL or 1100 mL of the NS with 20 mEq of KCL that can be given in the remaining 24 hours.

'

Finally, it makes sense! Thank you :)

abbyann · Jun 4, 2009

studystack.com. Has A LOT of flash cards. Tons of info. I'm sure there is quite a lot of math in it.

murphyle, BSN, RN · Jun 29, 2009

Hello everyone! I'd like to ask your assistance with the following question, which came up in my OB class today. Put simply, I don't understand the rationale behind this question AT ALL.

Q: You are caring for a 2618 g 32-wk premature infant, on a q3h feeding schedule, who took 5 mL of 24 cal Enfamil at the 0200 and 0500 feedings. You come on shift at 0800, and receive new orders for the following:

* Total fluid intake 120 mL/kg q24h

* Start D5 1/2NS IV to cover deficient PO intake

* Increase PO intake by 5 mL every other feeding, up to 25 mL/feeding

What is the PO feeding amount and the IV infusion rate at 0800?

What is the PO feeding amount and the IV infusion rate at 1400?

The infant regurgitates 4 mL from the 1700 feeding. What is the IV infusion rate now?

The instructor claims that every time either the PO or IV intake amounts are changed, the entirety of the previous intakes must be thrown out and everything re-calculated. She says that fluid intakes are calculated on a "rolling" basis, and that there is no set 24-hour period for calculating fluid intake - every time you change the PO intake or the infant refuses or regurgitates a feed, the clock starts on a new 24 hours and you recalculate everything to match the new intake for the next 24 hours. Using her algorithm, I came up with the following:

Total intake: 120 mL/kg/24hr x 2.618 kg = 314.16 mL/24hr

At 0200: 5 mL PO x 8 feeds = 40 mL/24hr

(IV fluids don't start till 0800, so we have no coverage to that point)

At 0800: 10 mL PO x 8 feeds = 80 mL/24hr; 314.16-80 = 234.16 mL/24hr IV; 234.16/24hr = 9.75 mL/hr

At 1400: 15 mL PO x 8 feeds = 120 mL/24hr; 314.16-120 = 194.16 mL/24hr IV; 194.16/24hr = 8.09 mL/hr

At 1700: 11 mL PO x 8 feeds = 88 mL/24hr; 314.16-88 = 226.16 mL/24hr IV; 226.16/24hr = 9.42 mL/hr

At 2000: 20 mL PO x 8 feeds = 160 mL/24hr; 314.16-160 = 154.16 mL/24hr IV; 154.16/24hr = 6.42 mL/hr

So over this 24-hour period, using her algorithm, we have:

(5 mL x 2 feeds) + (10 mL x 2 feeds + 9.75 mL/hr x 6 hr) + (15 mL x 1 feed + 8.09 mL/hr x 3 hr) + (11 mL x 1 feed + 9.42 mL/hr x 3 hr) + (20 mL x 2 feeds + 6.42 mL/hr x 4 hr)

10 + (20 + 58.5) + (15 + 24.27) + (11 + 28.26) + (40 + 25.68) = 232.71 mL

This isn't anywhere near 314.16 mL. Moreover, it seems to me that using her algorithm, since there is no set reference point for your 24 hours, you can never really know how much fluid your infant needs to take to meet the physician's fluid order. Finally, I did some research of my own, and I can't find one single reference in any of my books or in a CINAHL search to support her claim that the clock restarts on every intake change.

What am I doing wrong, or what did I misinterpret?

Thanks in advance for any assistance you might be able to offer!

Daytonite, BSN, RN · Jun 29, 2009

hello everyone! i'd like to ask your assistance with the following question, which came up in my ob class today. put simply, i don't understand the rationale behind this question at all.
q: you are caring for a 2618 g 32-wk premature infant, on a q3h feeding schedule, who took 5 ml of 24 cal enfamil at the 0200 and 0500 feedings. you come on shift at 0800, and receive new orders for the following:
* total fluid intake 120 ml/kg q24h
* start d5 1/2ns iv to cover deficient po intake
* increase po intake by 5 ml every other feeding, up to 25 ml/feeding
what is the po feeding amount and the iv infusion rate at 0800?
what is the po feeding amount and the iv infusion rate at 1400?
the infant regurgitates 4 ml from the 1700 feeding. what is the iv infusion rate now?
the instructor claims that every time either the po or iv intake amounts are changed, the entirety of the previous intakes must be thrown out and everything re-calculated. she says that fluid intakes are calculated on a "rolling" basis, and that there is no set 24-hour period for calculating fluid intake - every time you change the po intake or the infant refuses or regurgitates a feed, the clock starts on a new 24 hours and you recalculate everything to match the new intake for the next 24 hours. using her algorithm, i came up with the following:
total intake: 120 ml/kg/24hr x 2.618 kg = 314.16 ml/24hr
at 0200: 5 ml po x 8 feeds = 40 ml/24hr
(iv fluids don't start till 0800, so we have no coverage to that point)
at 0800: 10 ml po x 8 feeds = 80 ml/24hr; 314.16-80 = 234.16 ml/24hr iv; 234.16/24hr = 9.75 ml/hr
at 1400: 15 ml po x 8 feeds = 120 ml/24hr; 314.16-120 = 194.16 ml/24hr iv; 194.16/24hr = 8.09 ml/hr
at 1700: 11 ml po x 8 feeds = 88 ml/24hr; 314.16-88 = 226.16 ml/24hr iv; 226.16/24hr = 9.42 ml/hr
at 2000: 20 ml po x 8 feeds = 160 ml/24hr; 314.16-160 = 154.16 ml/24hr iv; 154.16/24hr = 6.42 ml/hr
so over this 24-hour period, using her algorithm, we have:
(5 ml x 2 feeds) + (10 ml x 2 feeds + 9.75 ml/hr x 6 hr) + (15 ml x 1 feed + 8.09 ml/hr x 3 hr) + (11 ml x 1 feed + 9.42 ml/hr x 3 hr) + (20 ml x 2 feeds + 6.42 ml/hr x 4 hr)
10 + (20 + 58.5) + (15 + 24.27) + (11 + 28.26) + (40 + 25.68) = 232.71 ml
this isn't anywhere near 314.16 ml. moreover, it seems to me that using her algorithm, since there is no set reference point for your 24 hours, you can never really know how much fluid your infant needs to take to meet the physician's fluid order. finally, i did some research of my own, and i can't find one single reference in any of my books or in a cinahl search to support her claim that the clock restarts on every intake change.
what am i doing wrong, or what did i misinterpret?
thanks in advance for any assistance you might be able to offer!

q: you are caring for a 2618 g 32-wk premature infant, on a q3h feeding schedule, who took 5 ml of 24 cal enfamil at the 0200 and 0500 feedings. you come on shift at 0800, and receive new orders for the following:

* total fluid intake 120 ml/kg q24h

* start d5 1/2ns iv to cover deficient po intake

* increase po intake by 5 ml every other feeding, up to 25 ml/feeding

what is the po feeding amount and the iv infusion rate at 0800?

po: 5 ml of enfamil + 5 ml of increased po intake (not specified if this po intake is enfamil or oral water) [13.09 - 10 = 3.09 deficient]

iv: you need to make up for hours 0600 and 0700 when the baby got no fluids (13.09 ml x 2 hours) so

13.09 ml needs to be infused over the next 3 hours

=

4.36 ml/hour

what is the po feeding amount and the iv infusion rate at 1400?

this is one of the every other feedings when the doctor wanted the po intake increased.

po: 5 ml of enfamil + 10 ml of increased po intake

iv: at 1100 hours the baby would have gotten 10 ml po (remember we're increasing the feeding amounts) + the remainder of iv catch up. they now need to give iv fluids to cover hours 1200 and 1300, or 26.18 + 3.19 ml from 1100 over the next 3 hours, or

9.79 ml/hour

the infant regurgitates 4 ml from the 1700 feeding. what is the iv infusion rate now?

the rates are pretty much the same because the 1700 hour feeding was not a feeding when there was no increase, so the rates didn't change: 26.18 + 3.19 + 4 ml (which must be replaced) = 33.37/3 hours =

11.1233 ml/hour

.

i may be calculating this wrong, but i am working from the viewpoint that the baby needs 13.09 ml/hour (120 ml x 2.618 kg/24 hours) and not including the current hour of feeding in the make up iv fluids until the next 3 hour round of fluids.

murphyle, BSN, RN · Jun 29, 2009

Hi Daytonite - thanks for the fast response!

"I may be calculating this wrong, but I am working from the viewpoint that the baby needs 13.09 mL/hour (120 mL x 2.618 kg/24 hours) and not including the current hour of feeding in the make up IV fluids until the next 3 hour round of fluids."

I started from those assumptions also, that the baby somehow needed to take in 314.16 mL over 24 hours (i.e. if the baby was NPO we'd run the IV at 13.09 mL/hr), that the PO and IV intakes should be balanced so that the hourly total always hit that number, and that any lost fluids should be made up in the IV. As a result, I turned in just about the same numbers as you posted. I was marked wrong.

Prof claims that instead of working on a set 24-hour period from 0000-2359 such as I was doing, that the clock restarts every time the intake changes, either up or down. When you bump up the PO feed and start the IV at 0800, the clock restarts such that now the baby has to take 314.16 mL from 0800-0759, and you assume that the PO feedings will not increase from that point forward, i.e. the baby will take 10 mL at every feeding thereafter. Likewise at 1400, it's a new 314.16 mL from 1400-1359, assuming 15 mL per feed and decreasing the IV to compensate.

If the baby spits up, refuses a feed or whatever, the lost fluid is not made up in the IV; instead the clock restarts using however much the baby did take as the PO figure and is recalculated for a new 24 hours. Likewise, the time that the baby was receiving no IV coverage does not figure in the 24-hour total, as the clock restarted when we started the IV. If, let's say that the baby's vein blew at 2100 and there was no IV fluid coverage for half an hour while we attempted to re-establish access, the clock would restart from that point, and the lost volume would not be added to the new IV.

Needless to say, that made no sense to me whatsoever. It seems to me that under Prof's algorithm, this patient is going to wind up very dehydrated.

Thoughts?

Daytonite, BSN, RN · Jun 29, 2009

Needless to say, that made no sense to me whatsoever. It seems to me that under Prof's algorithm, this patient is going to wind up very dehydrated.
Thoughts?

I agree with you. I would pray that only one of these problems shows up on her test and I wouldn't even bother answering it and just take the hit in points wrong. Or, you could sit in her office during office time and have her explain this again and again. Nail her down and find out if this is going to be on a test. She's probably a NICU nurse showing off. She probably had a heck of a time learning this herself and now she's getting her jollies watching you guys squirm with it.

I was an IV therapist. In the real world we would calculate the IV fluids on an hour by hour basis based on what the kid had taken in hourly. We did IV replacement for GI patients who were losing fluids from NG tube suction and that's how we did it. Whatever came out of the NG tube was what we programmed to give back through the IV.

murphyle, BSN, RN · Jul 6, 2009

Hi Daytonite--

Final verdict on the IV therapy question. I had the opportunity to speak with a NICU nurse on my unit last week, and she explained that the whole business with the clock resetting is because the MD "moved the goalposts" by ordering a new fluid intake. Along with the new fluid intake requirements, the patient gets a new 24 hours in which to meet those requirements. The previous whatever hours' intake doesn't disappear, as it's still calculated out at the end of the shift; it just doesn't spill over to the new orders, i.e. you don't count the 10 mL of formula the infant took three hours ago against the 15 mL q3h he/she is supposed to take now. Professor just did a less-than-optimal job of explaining the system. :bugeyes:

Incidentally, that question didn't recur on the test, either. Lucky break, that!

Thank you so much for the help - it was a much needed dose of sanity!

lovinngguds12 · Jul 20, 2009

I have taken up through Calc II and I tutor math at a local high school, so feel free to PM me with questions.

Ok I am still in my community college taking my libreal art courses and in a year and a half I will transfer them to a 4year college to bsn program. many schools give math tests though out the 4years, but I am poor un math how can I start now to gain confidence, i mean i cant even figure out some high school math. Is there hope 4 me?

Daytonite, BSN, RN · Jul 20, 2009

ok i am still in my community college taking my libreal art courses and in a year and a half i will transfer them to a 4year college to bsn program. many schools give math tests though out the 4years, but i am poor un math how can i start now to gain confidence, i mean i cant even figure out some high school math. is there hope 4 me?

it is success that helps people build confidence.

have you checked with your community college math or counseling department? all 3 community colleges that i went to over the years required that students had to take a math placement test before registering for any math classes except the remedial ones regardless of what math classes the student had taken in their past academic history. the math placement test was usually a one page quickie test that could be completed in less than an hour and graded in a few minutes. it guaranteed that a student didn't get registered in a math class that they wouldn't be able to handle. start with an easy math class and gradually work up to the more difficult ones. the math department counselors can tell you exactly the sequence of classes to take to accomplish that. pre-algebra (8th grade level math) is often the starting point. and when taking a math class, work homework problems + extra ones. getting good at math is about practice, practice, practice. math is so rational that once you have done hundreds of problems you should begin to see how logical it is. everything about math is one principle built upon another--and so on--like a link of chains. when one link of the chain is broken or missing is when people start to have problems doing math.

lovinngguds12 · Jul 21, 2009

Thank you so much, what scares me the most is the math tests give every semester in nusring school.