Another drug calculation problem

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Specializes in Med Surg/Tele/ER.

I thought I was pretty good at these.......but I cannot get the answer that was given. Show me my error please! Am I just having a dumb moment or what??? :imbar

Order reads 60 ml of 10% Glucose to infuse at 40 gtt/min. Using 60 gtt/ml tubing. How long will it take the solution to infuse?

I did 60ml x 60gtt / 60min = 60 min.

The correct answer is 1hr 30 min.

I thought I was pretty good at these.......but I cannot get the answer that was given. Show me my error please! Am I just having a dumb moment or what??? :imbar

Order reads 60 ml of 10% Glucose to infuse at 40 gtt/min. Using 60 gtt/ml tubing. How long will it take the solution to infuse?

I did 60ml x 60gtt / 60min = 60 min.

The correct answer is 1hr 30 min.

time= 60ml*60gtt/ml divided by 40gtt min

3600/40= 90 min

Specializes in Neuro, Critical Care.

i set the problem up using dimentional anaylsis.

first what unit of measurement do we want to end up with? Mintues right? (how long will it take)

so...set your equation equal to

min= 1min/40 gtt x 60 gtt/1 ml x 60 ml= 90 minutes

you always want to have the unit of measurement you want to end up with on the left side of your equation. Then I know that I dont want minutes to cancel off in my equation so I know my first conversion factor will be something with minutes on top (that way if minutes are on the top the units of measurement wont cancel off with the minutes on the left side of the equation..it will be this way in all your dimentional analysis equations..what ever is on the left side of the equation unit wise will be the top unit of measurement on your right side.)

...so what has minutes on top and something else on bottom? 1 minute/40 gtts...so drops (gtts) are now on the bottom and we want them to cancel off so our next conversion factor must have drops on the top (so that gtts will cancel)...so we look for the conversion factor with drops on the top...60 gtts/ 1 ml...now we know we want ml to cancel off so we multiply by 60 ml. You can also think of the 60 ml as 60 ml/1 and then you can see how the ml will cancel off...so now cancel all your units and you are left with minutes...do the math (1 x 60 x 60)/ (40 ) = 90 minutes..

if you set this up you will see that gtt's and ml's will cancel off and you will be left with minutes, which is what you want.

sorry if i confused you even further, dimentional analysis isnt the easiest to explain over the computer...good luck:)

Specializes in Critcal Care.

ELKmnin06 is right on the money with this. One other thing to remember when doing dimensional analysis is that you always have certain things "paired or married" to each other in the problem and you don't want to separate them when solving the problem. In your problem, 40 gtt is "married" to one minute, so keep them together. Likewise for 60gtt and one ml. Pretty soon you can work these and hardly read the question at all. It's easy as pie once you get the hang of it. Good luck.

I thought I was pretty good at these.......but I cannot get the answer that was given. Show me my error please! Am I just having a dumb moment or what??? :imbar

Order reads 60 ml of 10% Glucose to infuse at 40 gtt/min. Using 60 gtt/ml tubing. How long will it take the solution to infuse?

I did 60ml x 60gtt / 60min = 60 min.

The correct answer is 1hr 30 min.

Specializes in Med Surg/Tele/ER.

:imbar :imbar :imbar :imbar Thank ya'll & I usually do dimensional analysis....except on these problems I was taught the other way. I just missed the 40gtt/min for some crazy reason :smackingf. Thanks for getting me straighten out!:bow:

Specializes in Med/Surg..

Hi, We were taught several ways to do dosage calculations. Personally, I don't like dimentional analysis, too lengthy, too confusing. I use simple dosage ordered over dosage available. For your problem - very simple. 60ml @ 40gtts/min. 60 * 40 = 1.5 or 1 1/2 hours or 90 minutes. So, the 60ml of medication would be infused at 40gtts/min over 90 minutes. If you were using gravity instead of a pump, you'd want to count your drips and make sure that 40gtts were infusing per minute and if your calculations were correct - all 60mls of the medication would be infused over 90 minutes.

Ordered over available is just easier for some of us. This is a very simple example - Ex. Dr. orders 600mg of tylenol - it's available on the floor in 300mg tabs. 600 * 300 = 2. So you give your patient 2, 300mg tabs. There are also very simple methods for calculating pediatric dosages, etc.

Specializes in Neuro, Critical Care.
:imbar :imbar :imbar :imbar Thank ya'll & I usually do dimensional analysis....except on these problems I was taught the other way. I just missed the 40gtt/min for some crazy reason :smackingf. Thanks for getting me straighten out!:bow:

:) I like when ppl post dosage calcs, it gives me a chance to practice!!

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