Please explain to me why I set up this problem wrong. Dimensional Analysis

the way that problem was set up is really confusing. Just do your conversion one step at a time. Remember the unit you want should be on the top all the time

I always start out with the weight conversion .. just my preference but you don't have to.

117 lbs * 1 kg/2.2 lbs = 53.18 kg (put this answer aside, we'll use it later on)

Main problem:

30 ml/hr * 400 mg/500ml = 24 mg/hr (ml cancels out)

at this point you can do two things.. you can convert your answer mg/hr to mcg/hr or into mg/min. Eventually you want your answer in mcg/min.

24 mg/hr * 1000 mcg/mg = 24,000 mcg/hr (mg cancels out)

24,000 mcg/hr * 1 min/60 mins(hr) = 400 mcg/min (hr cancels out)

** since you want your answer in mcg/kg/min, you'd want to divide 400 mcg/min by 53.18 kg to get the dose PER KG (The value 400 mcg/min does not factor in the weight of the the patient; you need to include the weight in order to give the pt the correct therapeutic dose)

400 mcg/min divided by 53.18 kg = 7.5 mcg/kg/min (compare the 400 mcg/min vs 7.5 mcg/kg/min. Notice that w/o the weight factor in, the patient will get an excessive amount of dopamine)

Hope this helps.

I'm with Kris --

I always start out by looking at how the answer needs to be.. mcg/kg/min.. so I would start out by looking for mcg as well

thus the 1st step would be 1000 mcg/1 mg -- then just keep canceling out until you get rid of all the factors you don't need.

Okay, so how I begin this process is finding out the proportion of drug to total volume. So 400 divided by 500, leaves a ratio of 0.8mg per 1mL of solution. Since you have to know the ratio in mics, you simply move the decimal over to equal 800mcg per 1mL of solution. At this point make sure that the 400mg/500mL is equivalent to 400,000mcg/500mL. Wouldn't you agree this is the same?

Now, taking into consideration that there are 800mcg per 1mL, just multiply it by thirty. You should get 24,000mcg per 30mL of solution. This is the amount your patient is getting per HOUR.

So at this point you need to find out the dosage (24,000mcg per hour) divided by every Kg of your patient. If your patient weighs 117 pounds, convert pounds to kilograms, to get 53.1818182 Kg. At this point, you will have to look at your institution's rounding rules. If you round to the nearest whole number you would get 53Kg.

So how many micrograms is your patient getting per 1Kg? To find this answer divide 24,000mcg by 53Kg. You will get 452.830189mcg per 1Kg. Once again according to your institution there may be rounding rules. So lets stick with rounding to the closest whole number, 453.

At this point we know that your patient will be receiving 453mcg per 1Kg every HOUR.

Finally, you will need to take your dosage (453mcg for every 1kg) per hour and divide this by 60 minutes. So 453mcg divided by 60 minutes, gives you 7.55mcg/1kg/minute.

I know that this was a lengthy explanation but sometimes it helps to have a step by step instruction on dosage calculation. Remember, there is always more than one way to skin a cat, and as long as you get the right answer, and the right dose for your patient, you are administering a SAFE dose.

Hope this helps. Good luck!

SopranoKris! that absolutely makes sense. THANK YOU!!!!!

Everyone else who took the time to answer... Thank you!! :)