help w/ IV calculations

LaceyRN · Jan 19, 2008

we were supposed to study iv calculations friday in class but all we got was a woman stranding up there for about 7-8 minutes who never gave us a fully worked out problem nor the full formula to work the problem, so needless to say i am stumped and VERY frustrated. i have looked up some formulas in the books i have but i just recieved a practice test from my teacher and the formulas in the book won't work for the problems she gave us, or maybe it's just me and i'm just having a bad day!!!! either way i need some help please!!! here is as example of a problem i am stumped on:
*Give Bretylium 1g in 250 ml D5W at 2mg/min. Drop factor=15 gtt/ml. Calcualte the volume per hour.
The answer is supposed to be 30 ml/hr, but i don't know how to get that!???
i also need help w/ this one: give insulin 100 units in 1000ml NS at 6 units/hr. calculate the volume per hr.

Ok, I am great at math but not so great at teaching so bear with me!

Let's start with the 2nd one-it's easier.

#2: insulin 100u per 1000ml = 100u/1000ml, and the rate is 6u/hour so the calculation is:

(1000ml/100u) x 6u/hr = 60ml/h

now back to the first prob. it's asking for volume per hour which is a rate so the information given 15gtt/ml is extraneous and you don't use it.

#1: Bretylium 1g in 250 ml = 1g/250ml, and the rate is 2mg/min so to find volume/hr we want an answer in ml/h.

(2mg/m) x 60m/hr = 120mg/h (which is .120g/h)

(.120g/h) x (250ml/g) = 30ml/h

Hope this helps!!

Daytonite, BSN, RN · Jan 20, 2008

give bretylium 1 gram in 250 ml d5w at 2mg/min. drop factor=15 gtt/ml. calculate the volume per hour.

dose desired

: 2 mg/1 minute

dose on hand

: 1 gram/250 ml

conversion factor

: 1 gram = 1000 mg

conversion factor

: 60 minutes = 1 hour

you want to end up with

ml/hour

. the drip factor of the iv tubing is a red herring (distracter information) in calculating the volume per hour this iv will run and is not necessary information in determining the answer:

2 mg/1 minute

(dose desired)

x 60 minutes/1 hour

(time conversion factor)

x 250 ml/1 gram

(dose on hand)

1 gram/1000 mg

(conversion factor)

=

30 ml/hour

(dose to give, or volume per hour)

give insulin 100 units in 1000ml of ns at 6 units/hour. calculate the volume per hour.

dose desired

: 6 units/hour

dose on hand

: 100 units/1000 ml

6 units/1 hour

(dose desired)

x 1000 ml/100 units

(dose on hand)

=

60 ml/hour

(dose to give, or volume per hour)

i worked these by dimensional analysis which is, i think, is a much more efficient way to deal with problems, particularly when the information starts to get more complicated and involve more factors. still, the basic formuladose desired divided by the dose on hand times the amount the dose on hand comes in gives you the amount (or dose) to give. that formula will never steer you wrong. you only have to determine which terms are which. it could have easily worked for the second problem:

6 units

(dose desired

)/100 units

(dose on hand)

x 1000 ml

(amount the dose on hand comes in)

=

60 ml

there are tutorials on medication calculation plus weblinks to sites that have practice problems on post #3 of this sticky thread of the student forums: https://allnurses.com/forums/f50/nursing-math-thread-264395.html - the nursing math thread (in the general nursing student discussion forum). several of the tutorials are really good and you should take advantage of them. you can also see a whole bunch of problems worked out on this sticky thread:

https://allnurses.com/forums/f205/dosage-calculations-88867.html - dosage calculations (in the nursing student assistance forum).

ilovematt48 · Jan 20, 2008

thank you both VERY MUCH!!! I think i get it now! :idea: