Calculation question r/t rounding

[litchi]

I'm trying to figure out the concentration of a solution, then the concentration and volume per minute and hour. I mostly think I've got the hang of it, but I'm worried about knowing when to round. My instructor gave us this rule to follow for rounding: If it's over 1 mL, round to the nearest 10th. If it's under 1 mL, round to the nearest 100th. That being said, I have the following problem.

Heparin 1000 units in D5W 500 mL at 50 mL/hr

A. concentration of solution = 2 units/mL (1000 units/500 mL = ? units/mL)

B. vol/min = 0.83 mL/min (50 mL/hr x 1 hr/60 min)

C. vol/hr = 50 mL/hr (given)

D. concentration/min = 1.7 units/min (2 units/mL x 0.83 mL/min = 1.66 units/min)

E. concentration/hr = 102 units/hr (1.7 units/min x 60 min/hr)

I did everything right except in the book the answer for B was rounded to 0.8 mL/min, which threw my answers for D and E off as well. I can't find anything in the book regarding rounding (I'm sure it's there somewhere, I'm just not seeing it). I would just ask my instructor, but apparently the board we use to communicate is down for maintenance today.

Do you think my answers are still ok, given than I followed the rounding rule my instructor told us to follow or is there something else about IV solutions I should know? Any input is appreciated!

[ckh23, BSN, RN]

You can figure out each one without using a previous answer all of the information you need is given. Figure out each individually. On a side note double check the amount and volume because that concentration is way off. I have only seen concentrations of 25,000U/250 and 25,000U/500.

D)concentration=2U/ML *50ML=100U/HR (answer to E)

100U/60 min= 1.7U/min

You can figure it out to the nearest 100th, but most pumps are only going to program to the nearest 10th

[Music in My Heart]

I did everything right except in the book the answer for B was rounded to 0.8 mL/min, which threw my answers for D and E off as well.

You should never use rounded numbers as the input data for subsequent steps in serial calculations -- it introduces error at each step.

[Music in My Heart]

Heparin 1000 units in D5W 500 mL at 50 mL/hr

B. vol/min = 0.83 mL/min (50 mL/hr x 1 hr/60 min)

I did everything right except in the book the answer for B was rounded to 0.8 mL/min

There is 1 significant figure in the problem statement, therefore it is appropriate to have 1 significant figure in the answer.

[Mandychelle79, ASN, RN]

You should never use rounded numbers as the input data for subsequent steps in serial calculations -- it introduces error at each step.

Unless it is the way the teacher does it. I just had issues with our math test because of this. We can miss one. I use dimensional analysis, and convert weight right in the equation. Teacher does weights as an outside step and rounds. She did give me credit for it though

[Music in My Heart]

Unless it is the way the teacher does it. I just had issues with our math test because of this. We can miss one. I use dimensional analysis, and convert weight right in the equation. Teacher does weights as an outside step and rounds. She did give me credit for it though

Yes, true... even if you're teacher doesn't know what they're doing and insists on you doing it incorrectly, you should just do what they want... it's not worth trying to fight it.

Too bad so many nursing instructors are soooo bad at basic math and basic science.

[~Mi Vida Loca~RN, ASN, RN]

You will always need to go with what your instructor tells you for tests in school.

In our program we never round until the end. With that we round to the hundredth if it's under 1 and to the tenth of it's over 1 and with weights we always round to the hundredths.