IV math help

Hey everybody,
Im hung up on a couple IV problems:
Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
answer is 18.75 ml/hr
How do they get that?
Also
Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min
I have the answers but dont know how they got em.
Thanks ! 

Dec 3, '06Occupation: CDU nurse Joined: Sep '03; Posts: 4,001; Likes: 542Quote from FNPhopeful1. 40/3= 13.3 hours then 250/13.3= 18.79 ml/hrHey everybody,
Im hung up on a couple IV problems:
Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
answer is 18.75 ml/hr
How do they get that?
Also
Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min
I have the answers but dont know how they got em.
Thanks !
2. 75/60= 1.25 then 1.25 x 20= 25 gtt/min 
Dec 3, '06Joined: Jan '05; Posts: 162; Likes: 35Okay here goes...hope this helps:
I always use the "what you have and what you need" theory:
Ordered: Morphine sulphate 40mg in 250 ml to infuse at 3 mg/hr. How many cc's per hour will the infusion run?
answer is 18.75 ml/hr
So you have Morphine 40 mg/250ml = 250 divided by 40 = 6.25ml/1mg
What you need: How many ml = 3 mg/hr = 6.25 X 3 = 18.75 ml/hour
Does that make sense?
Okay #2
Ordered: 1000cc .45% NS at 75 ml/hr. Administration set: 20 gtt/ml. How should you regulate the IV? Answer is 25 gtts/min
75 ml/hr X 20 gtt/ml = 1500 gtt/ml divided by 60 minutes = 25 gtt/min
Hope this helps...it's hard to write it down so that it makes sense.
Jamie 
Dec 3, '06Specialty: med/surg, telemetry, IV therapy, mgmt ; Joined: May '05; Posts: 15,027; Likes: 8,983morphine sulfate 40mg in 250 ml to infuse at 3 mg/hr. how many cc's per hour will the infusion run?3 mg/1 hour (dose desired) x 250 ml/40 mg (amount you have on hand) = 18.75 ml/houryou set this equation up in order to manipulate and end up with the labels you want on the final answer.
1000cc 0.45% ns at 75 ml/hr. administration set: 20 gtt/ml. how should you regulate the iv?75 ml/1 hour (rate desired) x 20 gtts/1 ml (drip factor) x 1 hour/60 minute (conversion factor) = 25 gtts/minute 
Dec 3, '06Occupation: ICU RN Specialty: ICU,Oncology,School, ; From: US ; Joined: Sep '05; Posts: 135; Likes: 10hi,
i don't know how your school is teaching you to do math problems, but ours is using dimensional analysis. supposedly, it works with every problem if you use it the same way every time. i don't have enough experience to know if that's true, but i was able to figure out your questions using it, so maybe they are right!
here is how i did it:
1. always use the formula need = order x available
2. in the first problem, you need ml/hr.
ml
 =
hr
3. your order is 40 mg in 250 ml. because you know you want ml on top, reverse the numbers & make it 250ml/40 mg.
ml 250 ml
 =  x
hr 40 mg
4. finally, you have available, the ability to use 3mg in one hour.
ml 250 ml 3mg
 =  x  =
hr 40 mg one hour
5. you know your math will work because you can cross out the mg & you have ml/hour left for your answer.
a. 250 x 3 = 750
b. 40 x 1 = 40
c. 750 divided by 40 equals 18.75 ml per hour
the other problem works the same way.
need = gtts/min
order = 75 ml/hr
avail  20 gtts / ml
* with this one you have to use a conversion factor to get your hour into minutes. set it up like this:
gtts 75 ml 20 gtts 1 hour
 =  x  x 
min 1hr 1ml 60 min
75 x 20 x 1 = 1500
=  = 1500/60 = 25gtts/min
1 x 1 x 60 = 60
it has helped me to do every problem the same. hope this works for you also.
good luckLast edit by SchoolRN,BSN on Dec 3, '06 : Reason: Oops, didn't mean to duplicate Daytonite. I had to take my daughter's bf home before I finished...didn't see her reply. 
Dec 31, '06Specialty: Medical Telemetry ; Joined: Dec '03; Posts: 58; Likes: 10I didn't even post the question, but I'm thankful that you guys answered it so well! I do fine with dimensional analysis when it comes to everything except IV problems...they trip me up every time, and I have to pass the test on Tuesday! This helps very much!