Please Help with IV calculation homework

Nurses General Nursing

Published

Hello everyone...

Thank you in advance for reading my post. I am hoping someone can help me with my homework. My problem is:

"Another patient in CCU who weighs 142lbs is on Dobutamine infusing at 2 mcg/kg/min. Calculate the rate in:

___mcg/hr;___mg/hr; and ___mL/hr."

Now I figured out the mcg/hr=7,740 and mg/hr=4 but I am stuck on mL/hr. Can anyone help me? I would be so appreciative. Thanks again!!!:heartbeat

Oh...if you don't mind, would you please work it out, so I can see how you did it. Thanks a million!

roser13, ASN, RN

6,504 Posts

Specializes in Med/Surg, Ortho, ASC.

Maybe I'm just rusty, but it seems to me that you'd need to know the concentration (mg/ml) to figure out the ml/hr.

Is there any more info in the question?

BabyNurseBecky

14 Posts

Specializes in NICU.

I totally agree with roser13. There is no way to know how many mL per hour unless you know the concentration.

Also, maybe I am just rusty too (very possible), but are you sure it's 4 mg/hr???

RNRyan

9 Posts

Specializes in Cardiac.

Yeah, going along with what the people above me said-you need to know how many mcg/ml or mg/ml before you can figure out how fast to titrate that. And like what Becky said above me, I don't think that 4 is right. There are 1000 mg/mcg so taking that into account, 7740/1000= 7.74 mg/hr.

Hope that helps.

JaclynRN789

10 Posts

oh...thank you guys. Let me look at the order again...:D

scroopit

7 Posts

According to my drug references, dobutamine is available in 0.5mg/mL; 1mg/mL; 2mg/mL; and 4mg/mL in D5W for infusion. Your book should specify which ratio to administer. Good luck.

An example using the 0.5mg/mL:

7740mcg/hr X mg/1000mcg X mL/0.5mg = 15.48mL/hr

RNKPCE

1,170 Posts

If the strength is 400mg/250ml your drip rate would be about 4.7ml per hour. But you don't know the strength. Some doctors order double strength dopamine 800mg in 250ml, I have even seen triple strength once.

JaclynRN789

10 Posts

Dobutamine

Standard Concentration: 500 mg/250 mL D5W (Conc. 2mg/mL)

This is how I did the problem...

142lbs/2.2= 64.5kg

64.5x2=129mcg/min

129mcgx60=7740mcg/hr

7740mcg/1000=7.74mg/hr

7740mcg= ml

hr 2000mcg= 3.87 rounded to 4mg/hr

Now I just need to figure out mL per hour

Thank you all for taking the time to help me figure this out. I TRULY appreciate all your kindness.:heartbeat

JaclynRN789

10 Posts

uhmmm...is it 8.5mL/hr?

I am so bad with math :(

BabyNurseBecky

14 Posts

Specializes in NICU.

I would say it is 3.87 mL/hr. You need to divide the 7.74 mg/hr by 2 because there are 2 milligrams in each milliliter.

2mg 7.74 mg

______ = _______

1mL x mL

2x 7.74

___ _____

2 2

x = 3.87 mL (which I would guess would be rounded to 4)

I hope this is right - can someone else check my math. I am getting sleepy . . .

BabyNurseBecky

14 Posts

Specializes in NICU.

When I posted my reply, it messed up my spacing. I had everything spaced out so it looked like a math problem.

It should be 2mg/1mL on one side and 7.74mg/xmL on the other side.

Then, you do the math and it is 2/2x on one side and 7.74/2 on the other side. Therefore, x=3.87.

scroopit

7 Posts

250mL/500mg X 7.74mg/hr = 3.87mL/hr Round off to 4mL/hr.

Remember that the fractions that you use are equalities and be sure to set your problem up so that your units cancel out. For example: If 1mg = 1000mcg (an equality), then 1mg/1000mcg or 1000mcg/1mg. You can write the fraction either way because the values of the numerator and denominator are equal. You are therefore only multipling by "1" in an effort to manipulate the units. In the problem above, I went from mL/mg to mL/hr by multiplying by "1" (there is 7.74 mg of medication being instilled in 1 hour of time; therefore 7.74mg=1hr). Sorry if I confused you more. Good luck.

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