Dosage Calculation ???

a solution of 400 mg dopamine hcl in 250 ml of d5w is infusing at 20gtt/min. calculate the mcg/min dosage.

actually, yes this is solvable, but it is missing the drop factor of the iv tubing being used. you know the formula, dose desired divided by dose on hand? it does have another part to it if you carry it through: equals dose to give. what you have here is a problem that is playing around with plugging figures into the equation and leaving you to find the desired dose. desired dose is usually information that is given to you in a problem, not being asked for. fooled you, didn't they? make a picture to help yourself understand what i am saying.

that's the problem you need to solve. it's going to require a conversion factor (mg to mcg) and how the heck you get from ml's to gtts? you are missing the drop factor (drops/milliliter) of the tubing being used. now, this may be a mistake on the part of the instructor, but maybe not. they may be testing your knowledge of iv tubing. there are 2 different kinds of tubings that can be used:

• microdrip (or pediatric) tubing which delivers 60 gtts/ml
  
• macrodrip tubing delivers at different rates based on the manufacturer specifications
  • 10 gtts/ml
    
  • 12 gtts/ml
    
  • 15 gtts/ml (probably the most common, often called standard tubing)
    
  • 20 gtts/ml

the answer to the question might be "there is not enough information to solve this problem"

the "a" answer, at least the brown noser answer, the "go to the head of the class answer", might be to use all the various drop factors to get the following solutions. take a deep breath and begin (once you get the first calculation, you just substitute [i'll be copying and pasting] the drop factor into the remaining calculations. remember, you want to end up with "mcg" in the numerator and "minutes" in the denominator, so you manipulate the ratios to yield those labels in their correct positions for you while maintaining relationships within their proper ratios.

fyi. . .dopamine is usually ordered by the doctor as mcg/kg/min. you can also calculate a possible weight on this patient if you know what that mcg/kg/min figure is! let's have some fun.

be aware that you can rework any med calc problems once you have all three elements of the dose desired divided by dose on hand equals the dose to give formula. all you have to do is replace one of the three figures with the dreaded "x" and solve for it. most problems don't ask you for the dose desired or the dose on hand, but a tricky instructor might do it to see if you know how to do the math! these kinds of questions are what the guys in premed used to call "ace-breakers", separate the thinkers from the rest of the pack and make the difference between an "a" and a lower grade.

Whoa! Is that hokey, or what? Go get your "A".