IV Dosage Calculations... HELP!

Boog'sCRRN246, RN · Feb 12, 2011

Hopefully, everything will make sense

For #1, I got 83mL/hr and 21gtt/min.

For drip rate, you can use the magic number method which is 60 divided by gtt size (which in this case would be 60/15gtt set = 4)...so once you find your flow rate (83mL/hr) you'd divide 83 by 4 and that will give you your gtt/min. Or you can work it out, which would be 15gtt/1mL = Xgtt/83mL, X = 1245gtt/hr, 1245gtt/60min = Xgtt/1min, X = 21gtt/min.

For #2, I got 23mL/hr and 8gtt/min.

40000units/500mL = 1800units/XmL, X = 23mL/hr.

Again for drip rate, you can do 60/20gtt set = 3, 23/3 = 8gtt/min...or worked out 20gtt/1mL = Xgtt/23mL, X = 460gtt/hr, 460gtt/60min = Xgtt/1min, X = 8gtt/min

So, magic number method:

60gtt set = 60/60gtt set...magic number = 1

20gtt set = 60/20gtt set...magic number = 3

15gtt set = 60/15gtt set...magic number = 4

10gtt set = 60/10gtt set...magic number = 6

JSTARZ · Feb 12, 2011

OK. #1 83 mL/hr is correct however 6 gtt/min is incorrect. The key to drops per minute is to remember this is a two step calculation.

First: determine flow rate or amount to be infused (in mLs)/ time (in hours)

ex: 1000 mL/12 hr=83 mL/hr

Second: determine drops per minutes.

gtt/min= flow rate (mL/hr)/60 (minutes) X gtt factor

ex. 83 mL/hr/60 mins X15 gtt=21 gtts/min

the 60 is constant it shall never change in this formula.

#2. Completely wrong. =). To work problems like this you can use simple ratio and proportion.

40000U/500 mL=1800U/X mL. you then cross multiply and solve for X. THis will yield mL/hr. Then you continue on as above with the formula for gtts/min. You should get 23 mL/hr and 8 gtts/min. Hope this helps.

PinkNBlue, BSN, RN · Feb 13, 2011

IV calcs always threw me until one day it just 'clicked'. Hopefully this will help a bit!

You're right on number one with the ml/hr answer. Those are pretty simple with dividing the total volume with the number of hours you're infusing so 1000/12=83.3333 or 83ml/hr.

Drip rates I use the magic number system which makes it so much easier so memorize those and you'll have no problem. :)

60gtts/min=1 (so if the tubing was 60gtts/min, you'd divide your ml/hr answer by 1 which would give you a drip rate of whatever your answer was for ml/hr. This is also what microdrip tubing is divided by if a problem says 'using microdrip tubing').

20gtts/min=3 (because 20 goes into 60 3 times) so you'd divide the ml/hr by 3 which would give you the gtts/min.

15gtts/min tubing=4 (because 15 goes into 60 4 times) so you'd divide the ml/hr by 4 which would give you the gtts/min.

10gtts/min=6 (because 10 goes into 60 6 times) so you'd divide the ml/hr by 4 which would give you the gtts/min.

So for the first problem, the tubing is 15gtts. So you have your hourly rate of 83ml/hr. You'd then take 83 and divide it by 4 so 83/4=20.75 but since you cannot have 0.75 drip, you'd round to 21gtts/min. If this problem said tubing with 10gtts, you'd take 83 (hourly rate)/6=13.8 or 14gtts/min. Does that make sense??

For number two, whenever you have a Heparin scenario, remember that Heparin is usually very slow to infuse so you're going to have a lower number of ml/hr and a low drip rate. I had a calculation test and had a Herpain scenario and questioned myself many times before remembering Hep is slow to infuse so a low answer is not necessarily incorrect. For this problem, you have to do your basic desired amount/available x your vehicle. So you have 1800 units of Heparin ordered and 40,000 units on hand... 1800/40,000=0.045 units. But now you have to multiply your answer by 500ml (your vehicle because ml is what you'll be infusing... not units) so 0.045 units x 500ml= 22.5ml/hr is your hourly rate.

Now you take 22.5ml/hr and divide by your magic number drip rate which because the problem says the tubing is a 20 gtts set, you know that the magic number is 3... so 22.5/3= 7.5 which rounds to 8gtts/min since you cannot give half a drip.

Hopefully this makes a little bit of sense... it's hard not having a piece of paper to write it all out on so you can better understand it. But just know I've been there. One day (soon!) it'll just click. Once you get to piggybacks, let me know if you need help! Helping keeps me current too :) Good luck!!

CrazierThanYou · Feb 13, 2011

Thanks guys! I think I have finally figured it out with everyone's help! :)

Kayjaymack · Apr 2, 2014

Help I'm lost

#1

pepcid 20mg/50ml D5W over 30 min

using a 15gtts/min adm set

administer:__________

#2

1000ml D5 0.45% NS @50hr

available 15gtts/ml adm set

Kandy83 · Apr 3, 2014

Help I'm lost
#1
pepcid 20mg/50ml D5W over 30 min
using a 15gtts/min adm set
administer:__________
#2
1000ml D5 0.45% NS @50hr
available 15gtts/ml adm set

Please write down the full equation. Also write down the answer that you have came up with. We will not do your home work for you. :no:

Esme12, ASN, BSN, RN · Apr 3, 2014

Help I'm lost
#1
pepcid 20mg/50ml D5W over 30 min
using a 15gtts/min adm set
administer:__________
#2
1000ml D5 0.45% NS @50hr
available 15gtts/ml adm set

PLease show us your work so we know how to best help you.

[TABLE=class: fraction]

[TR]

[TD=class: numerator]Volume (mL) x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min)[/TD]

[/TR]

[TR]

[TD=class: denominator] Time (min) [/TD]

[/TR]

[/TABLE]