This is a simple formula that uses linear algebra and a little fraction/cross multiplication action. I use this one quite often. Then, I double check with a flow rate calculator on my PDA. lol
So let's say you are going to hand a dopamine infusion. You have 400 mg in 250 ml of solution. You want to start your infusion at 10 mcg/kg/min. The patient is 70 kg.
First, I want to know how many mg an hour I will need to give this patient. I take 10 and multiply by 70. This gives me mcg per minute.
This should be 700 mcg.
Next, I want to know how many mcg an hour I will be giving. So, I take 700 and multiply by 60. (60 minutes in an hour) This should equal 42,000 mcg.
Now, I want to convert the mcg to mg so I am working with the same units of measure throughout my formula. Remember, 1000 mcg equals 1 mg. So, we simply divide 42,000 by 1000. This should give us 42 mg per hour.
Now we have all of the information we need to set up our formula.
On the left side, I set up what I have on hand. 400mg
On the right side I set up what I need to give. 42mg
The X will be ML/hr.
The completed formula should look like this:
250 ML X ML
Now, we cross multiply and solve X.
Cross multiply first, and we have: 400X = 250 multiplied by 42.
The result should be: 400X = 10, 500
Now we simply treat this like linear algebra and divide both sides by 400 and isolate X.
400X divided by 400 = X and 10, 500 divided by 400 = 26.25
So, X= 26.25 ML/hr. Most will round down to 26 Ml/Hr.