# help, my math is less than perfect!

1. I came across a website and I am trying to learn how to calc meds to get ahead start before that section comes up because it will be my weakest. This is the problem... I came up with an answer of 20 is this problem worded wrong or am I not getting it?

1 litre of 5% Dextrose in 0.9% sodium chloride is prescribed over 7 hours. The drop factor is 20. The infusion has been going for 2 hours and 6 minutes. 300 millilitre remains. What is the drip rate (drops / minute) required to ensure the infusion finishes on time?

Volume to infuse = 1 litre - 300 millilitre = 700 millilitre
Time for infusion = 7 hours - 2 hours and 6 minutes = 4 hours and 54 minutes
The formula for calculating drip rate is:

volume (ml) X drop factor (drops/ml)
-------------------------------------- = drops / minute
time (min)

Place the values in the formula:-
700 X 20
----------
294
14000
= ----------
294
= 47.6190476190476 drops / minute

Why are they using 700????

Also can anyone suggest a drug calc book for dummies? My test book does not give enough examples.

thanks !
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Joined: Mar '09; Posts: 28; Likes: 3

3. Quote from pupsnpaws
I came across a website and I am trying to learn how to calc meds to get ahead start before that section comes up because it will be my weakest. This is the problem... I came up with an answer of 20 is this problem worded wrong or am I not getting it?

1 litre of 5% Dextrose in 0.9% sodium chloride is prescribed over 7 hours. The drop factor is 20. The infusion has been going for 2 hours and 6 minutes. 300 millilitre remains. What is the drip rate (drops / minute) required to ensure the infusion finishes on time?

Volume to infuse = 1 litre - 300 millilitre = 700 millilitre
Time for infusion = 7 hours - 2 hours and 6 minutes = 4 hours and 54 minutes
The formula for calculating drip rate is:

volume (ml) X drop factor (drops/ml)
-------------------------------------- = drops / minute
time (min)

Place the values in the formula:-
700 X 20
----------
294
14000
= ----------
294
= 47.6190476190476 drops / minute

Why are they using 700????

Also can anyone suggest a drug calc book for dummies? My test book does not give enough examples.

thanks !
They are using 700 because in order to subtract 300 milliliter from 1 liter, you have to convert liters into milliliters.
1 liter = 1000 mL, so you would subtract 1000mL -300mL= 700 mL.

A much easier way to do this problem would be to take 1L and convert it into mL, which would equal 1000mL
Then divide 1000ml by 7, which would equal 142.85714(this is the drops per hr), then use this formula: volume(mL)/ 60(min) x drop factor.

142.85714 / 60(min) x 20(drop factor)

you can reduce this to 142.85714 / 3.

Now divide 142.85714 by 3 which equals 47.619047
The drop factor would be 48( you would need to round to the nearest whole # because you can't half a drop)
Last edit by ladynurse1 on Apr 25, '09
4. Yes I understood that part but don't you use the 300 because they ask how long it will take to finish the infusion. Isn't the 700ml gone?
5. take a look at my post. I just edited to add something. Let me know if this helps. If not, I will make you a word document that will make more sense.
6. Wow... I still dont get it. Thanks for your help I still don't understand if only 300ml is left why are they using 700mg in the calc. To me it seems like you had 1000 and now 300 is left you would calculate how long to infuse 300. God help me!
7. so when i read the problem, i knew that the order wanted 1000ml to be infused over a period of 7 hours. after 2 hours and 6 minutes, 700 ml of the solution has been infused.

700 should not be used. the 700 is gone and already in the patient. 300 is the VTBI factor in this problem. pull out the information you NEED.

"1 litre of 5% Dextrose in 0.9% sodium chloride is prescribed over 7 hours. The drop factor is 20. The infusion has been going for 2 hours and 6 minutes. 300 millilitre remains. What is the drip rate (drops / minute) required to ensure the infusion finishes on time?"

the formula to figure this problem out is correct.

volume in milliliters to be infused
______________________________ x drip factor

time in minutes

300ml
_____ x 20
294 minutes

the answer is 20 drops per minute. you are correct.

if you were to infuse the solution @ 47 drops per minute, the infusion would finish in much shorter of a time than ordered. you have 300 ml to infuse over a period of 4 hours and some change. if there are 20 drops per each ml x 300ml, thats 6000 drops. divide that by the number of minutes (294), and your answer is still 20.

i dont know why that website says that 48 is the answer.
8. your textbook is showing an incorrect solution to this problem. the 47.619 drops/minute would have been the infusion rate for the 1 liter bag if it had been infusing on time at 142 cc/hour like it was supposed to! it is a fluke that 700 mls over 294 minutes with 20 drop tubing also happens to work out to the same number of drops/minute. i worked out both figures twice because it was confusing to see the same final calculations end up to be the same answer. however, your textbook is still incorrect. you should write a letter to the publisher pointing out the error along with the correct solution.
[font=courier new]
[font=courier new]1 litre of 5% dextrose in 0.9% sodium chloride is prescribed over 7 hours. the drop factor is 20. [font=courier new]the infusion has been going for 2 hours and 6 minutes. 300 millilitre remains. what is the drip rate (drops / minute) required to ensure the infusion finishes on time?
this is how i calculate the answer. . .
1 liter (1000 ml) over 7 hours would be 1000 ml/7 hours for 142.85714 ml/hour

the problem is telling us that after 2 hours and 6 minutes 700 mls of the iv fluid was infused. so, for the remaining 4 hours and 54 minutes the 300 mls will need to be infused in order to be in compliance with the order that was prescribed: to infused 1 liter (1000 ml) over 4 hours.
300 ml + 700 ml = 1000 ml
2 hours and 6 minutes + 4 hours and 54 minutes = 7 hours
to make this easier, i suggest that the hours and minutes be converted to minutes now. there are 60 minutes in each hour:
4 hours and 54 minutes = 294 minutes
rewrite the problem: 300 ml to be infused over 294 minutes with tubing that has a drop factor of 20. what is the drip rate in drops/minute so that the infusion finishes on time?
300 ml (volume to be infused)/294 minutes (time to be infused) x 20 gtts/ml (drop factor of iv tubing) = 20.408 gtts/minute, rounded to 20 gtts/minute
this sticky thread on the general nursing student discussion forum has free online tutorials for how to do medical calculations. see post #2 for the weblinks: http://allnurses.com/general-nursing...ad-264395.html - the nursing math thread
9. I was thinking that you would have to set the infusion rate in the beginning. That's how I'm coming up with 48. If you are infusing 1000mL over 7 hrs, I would set the infusion rate at 48, but I guess the problem is just asking about the 300 ml over 4hrs and 54 min. Thanks for chiming in Daytonite and flightnurse
Last edit by ladynurse1 on Apr 25, '09