Math...again

Music in My Heart · Nov 26, 2007

here i am once again. i do not understand the drip factor stuff. i have an order of aminophylline 1gm in 500 cc d5w to infuse at 0.5mg/kg/hr for a pt weighing 154.
the first question is what is the hourly amt the pt is to receive i got 35 mg/hr
second, how many gtt/min should the iv run if the drop factor is 60gtt/ml.
i set it up this way and have gotten an off the wall 8.3
500ml/x = 60gtt/1ml ...that cross multiplies to 500=60x divide 500/60...and i got 8.3.
am i doing this right? :o

here's what i get:

if the "154" means "154 kg" then 0.5 mg/kg/hr x 154 kg = 77 mg/hr

if the "154" means "154 lb" then 0.5 mg/kg/hr x 154 lb x (1 kg/2.2 lb) = 35 mg/hr

35 mg/hr x (500 ml/1 gm) x (1 gm/1000 mg) = 17.5 ml/hr (recall 1 cc = 1 ml)

17.5 ml/hr x (1 hr/60 min) x (60 gtt/1 ml) = 17.5 drips per min

SarasotaRN2b · Nov 29, 2007

Here's what I get:
If the "154" means "154 kg" then 0.5 mg/kg/hr x 154 kg = 77 mg/hr
If the "154" means "154 lb" then 0.5 mg/kg/hr x 154 lb x (1 kg/2.2 lb) = 35 mg/hr
35 mg/hr x (500 ml/1 gm) x (1 gm/1000 mg) = 17.5 ml/hr (recall 1 cc = 1 ml)
17.5 ml/hr x (1 hr/60 min) x (60 gtt/1 ml) = 17.5 drips per min

Would this be rounded up to 18 gtt/min?

Music in My Heart · Nov 29, 2007

Would this be rounded up to 18 gtt/min?

I don't really know. If you're following the rules of significant figures then yes, there would only be 2 significant figures and you would round up.

Not being a nurse yet, I don't know what they'd do in clinical practice.

Daytonite, BSN, RN · Nov 29, 2007

Would this be rounded up to 18 gtt/min?

Yes. In the real world of nursing, there is no such thing as a 17.5 drop. You would be standing looking at the drip chamber of the IV tubing with your watch next to it and counting the number of drops as they fall in terms of whole numbers and noting the sweep hand as it goes around on your watch.

Cosper123 · Nov 30, 2007

Here's what I get:
If the "154" means "154 kg" then 0.5 mg/kg/hr x 154 kg = 77 mg/hr
If the "154" means "154 lb" then 0.5 mg/kg/hr x 154 lb x (1 kg/2.2 lb) = 35 mg/hr
35 mg/hr x (500 ml/1 gm) x (1 gm/1000 mg) = 17.5 ml/hr (recall 1 cc = 1 ml)
17.5 ml/hr x (1 hr/60 min) x (60 gtt/1 ml) = 17.5 drips per min

"I have an order of Aminophylline 1gm in 500 cc d5w to infuse at 0.5mg/kg/hr for a pt weighing 154. "

The way I read this, the 500ml/gm is moot since we are given the hourly rate. So, assuming the 154 was pounds, I worked it as such:

Using this formula -

Order/Time X drop factor /60 minutes

Where Order/Time would normally give the hourly rate.

35mg x 60gtt /60min = 35

Is there something that I missed or did someone else get 35 drops?

Music in My Heart · Nov 30, 2007

"I have an order of Aminophylline 1gm in 500 cc d5w to infuse at 0.5mg/kg/hr for a pt weighing 154. "
The way I read this, the 500ml/gm is moot since we are given the hourly rate. So, assuming the 154 was pounds, I worked it as such:
Using this formula -
Order/Time X drop factor /60 minutes
Where Order/Time would normally give the hourly rate.
35mg x 60gtt /60min = 35
Is there something that I missed or did someone else get 35 drops?

I don't use formulae; I just reason my way through it the problem. My logic appears sound but perhaps someone will point out an error that I've made.

The problem with your equation (35mg x 60gtt /60min = 35 drops) is dimensional inconsistency. The units of your answer would be mg-drops/minute, not drops.

Cosper123 · Nov 30, 2007

Yep, should read 35 drops per min.

And that's why I use formulas instead of trying to reason my way through a problem :)

Music in My Heart · Nov 30, 2007

Yep, should read 35 drops per min.
And that's why I use formulas instead of trying to reason my way through a problem :)

The problem is, you've still got your dimensional inconsistency.

35mg x 60gtt /60min DOES NOT = 35 drops/minute. It equals 35 mg-drops/min which are not usable units.

That's why I reason my way through problems. It won't guarantee a correct answer but it will avoid some incorrect ones.

Perhaps Daytonite will take a peek at this post point out the flawed reasoning (whose ever it is...). If it's mine, I welcome the correction because I just hate not understanding things and this, I think that I do.

Cosper123 · Dec 1, 2007

Yeah I wouldn't be applying your dimensional logic to my explianation of the formula because I really don't worry about the details to that degree.

All I know is the order divided by time is your hourly rate, and then multiply that by the drop factor and divide by 60 and you get the drips per min.

And with that I got 35. And yes please someone else work the math out here and see what you get...I'd especially like to know the answer if I'm wrong as it would give me an opportunity to improve.

Daytonite, BSN, RN · Dec 2, 2007

The problem is: Aminophylline 1gm in 500 cc D5W to infuse at 0.5mg/kg/hr for a patient who weighs 154 pounds. How much of the drug should the patient be receiving each hour? Then, how many drops per minute will the IV run if the drop factor of the IV tubing is 60gtt/mL?

1 gram in 500cc (or mL) is 2mg/mL.

If the patient weighs 154 pounds he should get 35mg, and this would be a per hour dose:

0.5 mg/kg

(dose desired)

x 154 pounds

(patients weight)

x 1kg/2.2 pounds =

35 mg

(dose to give)

The drip rate will be 18 gtts/minute rounded off from 17.5

500mL/1 gram

(dose on hand)

x 35 mg/hour

(dose desired)

x 60 gtts/1 mL

(drip factor of IV tubing)

x 1 gram/1000mg

(conversion factor )

x 1 hour/60 minutes

(conversion factor)

= 17.5 gtts/minute = 18 gtts/minute

rounded off

Hope that helps clear up the controversy of this problem for you.

Cosper123 · Dec 2, 2007

Thank you for clearing it up Daytonite!