Math...again

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

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?

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.

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?

"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.

Yep, should read 35 drops per min.

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

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.

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.

Thank you for clearing it up Daytonite!

Yep, should read 35 drops per min.

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

Butyou have to use the right formula! What's wrong with reasoning through a problem?

One of the things that I have found that helped (besides the great assistance from Daytonite!) is that when I am looking at a calculation program, I will write down the info given, what you are trying to find AND any conversion factors.

If I am looking for a flow rate of drips/min...I will immediately place that to the right of my equals sign ( ...... = gtt/min). Then I will look for the info given and the first thing I will look for is the gtt/ml and that is the first thing I will write on the left (gtt/ml + .... = gtt/min). I'll then look at the other information given and put it in so that by doing dimensional analysis, I'll find myself with my final answer being gtt/min.

If I can't cross off everything but that, I know that I made some error in setting up the problem.

I have to say that the best thing I learned in chemistry was the use of dimensional analysis and the use of conversion factors.

Kris