Need Help with Dosage Calculation

nurseprnRN, BSN, RN · Jul 26, 2013

Rather than show you how I would solve this addition and division problem, I'd like to see if I can help you see how to think about it. Your goal here is NOT to derive some fancy formula or have one to memorize to plug in as many numbers as there are in the whole set-up given you by your faculty. Your goal is to be able to think about the situation and visualize what runs when and how much fluid of different kinds are given such that the total is 1500cc. This is because this sort of situation may very likely happen in your practice, and you need to know how to think about it so you can figure out what to do.

It might be helpful to start by actually drawing a picture, or writing down a list of all 24 hours in a day in one-hour blocks, and color in the blocks to show where the piggybacks are being given and how much they are. I know, sounds silly. Indulge me.

How many cc's do they add up to in a day? (note, it doesn't matter at all how many mg of drugs or what kind of IV fluids there are in them. This is strictly a problem of total fluid volumes, right?)

How many minutes (hours) are involved in running them piggybacks?

So, if you can give a total of 1500 cc from all IV sources, how many ccs do you have left to give from the maintenance IV?

For ease in calculation, how many cc/hour is that? Yes, you can run the maintenance IV while the piggybacks are running. Your sole concern is being sure that your patient only gets a total of 1500 cc in the 24 hours.

What do you get?

Esme12, ASN, BSN, RN · Jul 27, 2013

Restricted Fluids: 1500 mL/24 hours
Primary IV of D5LR running via infusion pump
Ampicillin 3g IVPB q6h in 100 mL of D5W over 30 minutes each
Gentamycin 170 mg IVPB q8h in 50 mL NSS each to infuse over 1 hr

A. Calculate IVPB flow rates: Ampicillin: __mL/hr Gentamycin __mL/hr
B. Calculate the total IVPB time: ___ hrs
C. Calculate the total IVPB volume: ___mL

This is a great site...DosageHelp.com - Helping Nursing Students Learn Dosage Calculations since this is your first math here lets break it down.

.......how fast does the pump need to go if you have to give 100mL of fluid over 30 min

[TABLE=class: fraction]
[TR]
[TD=class: numerator][/TD]
[/TR]
[TR]
[TD=class: denominator]100 ml (amount to give)/30 minutes (time over which it is to be infused) x 60 minutes/1 hour (conversion factor) = 200 ml/hour (infusion rate to program on the iv pump)[/TD]
[/TR]
[/TABLE]

Now the Gentamycin......

50mL (amount to give)/60min (time to be given) x 60min/1hr (your conversion factor) = 50mL/hr

If you are giving one 4 times (q6hr) in 24 hours over 30 mins

4doses x 30min = 120mins How many hours are in 120 mins 120min/60min/hr = 2 hours

and the other 3 times (q8hr) in 24 hours over 1 hour

3 doses at 1 hr a piece.....3 x 1 = 3 hrs

so the total in infusion time is

2 hours(for ampicillin) + 3 hours (for gentamycin) = 5 hours total IVPB infusion time

Now you need total IVBP volume. You have 100mL of one infusing 4times in 24 hours

100mL/1dose x 4 doses = 400mL

You also have 50mL of the other infusing 3 times in 24 hours

50mL/1dose x 3 doses = 150mL

So if one is 400mL total and the other is 150mL total the total is....

400mL + 150mL = 550ml total

Esme12, ASN, BSN, RN · Jul 27, 2013

We now know these answers

A. Calculate IVPB flow rates: Ampicillin: 200mL/hr Gentamycin 50mL/hr
B. Calculate the total IVPB time: 5hrs
C. Calculate the total IVPB volume: 550mL

Lets figure out these

D. Calculate the total primary IV volume: __ mL
E. Calculate the total primary IV time: __ mL
F. Calculate the primary IV flow rate: __mL/hr

If we know that this patient has already received a total of 550mL's of IVfluid in meds alone...and they can have NO MORE than 1500 in 24 hours....how much fluid is left over to give 1500mL (total allowed) - 550mL (already given) is 950mL's left over to be given in the next 24 hours.

1500mL - 550mL = 950mL

We know that the IV meds take up a total of 5 hours every day how many hours are left over to infuse the rest of the IVF. There is 24 hours in a day and 5 hours are already taken leaving 19 hours left over

24hr - 5hr = 19hours

Now we need to infuse the remaining 950mL of fluid over 19 hours.....at what rate would you set the IV pump?

950mL/19hr = 50mL/hour

The next one you will show me and figure out what you don't understand.