# Critical care math using dimensional analysis

- 0Jul 15, '13 by RetrieverGirlI need help with dosage calculations for critical care. Does anyone know how to use dimensional analysis? I need help on mcg/min and mcg/kg/min drip rates. I need a good website with some practice questions also.
- 2Jul 15, '13 by FineAgain, BSN, RNHere is the site that helped me the most:

DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

Do you have to use dimensional analysis? I always thought it was too many steps to get to the same answer. - 1Jul 15, '13 by lorirn2bQuote from arrisubI agree! I definitely prefer proportion method.Here is the site that helped me the most:

DosageHelp.com - Helping Nursing Students Learn Dosage Calculations

Do you have to use dimensional analysis? I always thought it was too many steps to get to the same answer.llg likes this. - 1Jul 15, '13 by bluedove1If you stick with dimensional way you are set....it will become second nature to you...the reference website is really goodRetrieverGirl likes this.
- 2Jul 16, '13 by Streamline2010Dimensional is also called Factor Label Method. I used it in engineering. Having all of the units cross out at the end so that you are left with just the correct units (mg, mm, lb, kg, volume per minute, whatever you wanted) is a nice check that you set up the equation correctly and have solved it correctly.♪♫ in my ♥ and GrnTea like this.
- 2Jul 16, '13 by
*GrnTea*, BSN, MSN, RNMy only caveat about DA (other than it is often more complicated than necessary) is that so often I see students try to cram every possible bit of data in the question into the equation...and a lot of it is not needed for the answer. Examination writers know this and put distractors (wrong answers) that would result from doing that in the choices. Does make for a lot of confusion, and we see it here often.

Step back from every problem and ask what's really being asked, see if you can eyeball a possible answer range, and then determine how to solve for X in any way that works comfortably for you.RetrieverGirl and llg like this. - 1Another problem with Dimensional Analysis (DA) is that it doesn't always work well in real-life situations. Sometimes, in actual clinical practice, the situation doesn't "fit" dimensional analysis very well. But I have never met a problem that didn't lend itself to the old proportion way of calculating things.

A third problem -- which is perhaps my biggest gripe about Dimensional Analysis -- is that I see many students and new nurses using it to "solve" math problems without really understanding what is going on with the situation. Taking care of a patient requires more than just solving an equation, it requires an understanding of the relationships between volumes, rates, dosages, etc. When young nurses just plug numbers into an equation and get an answer (as if for a test question), they often miss what is actually happening with the fluid/medication/etc. and the patient. The proportion method promotes an understanding of the quantities of meds/fluids/etc. involved -- and that understanding is important for optimal patient care.

DA can work for test questions ... particularly if the questions are chosen to be well-suited for DA. But its weakness show when the new grads struggle with actual practice situations.GrnTea likes this. - 0Jul 16, '13 by RetrieverGirlHonestly I don't always use dimensional analysis. But for some math problems it makes better sense to me. I also use ratio and proportion. I just want to get those this critical care math.
- 1Jul 16, '13 by bluedove1Why don't you post one of your critical care problems so we can see what you are having problems with. I find if you don't have a good grasp of DA and if you try to go between using DA and proportion you will get confused and screw up...DA is what I learned in chemistry....for me DA is so much easier once you learn it and really apply it without switching back and forth..jmhoEsme12 likes this.
- 1Jul 16, '13 by SlinkyheadRNI always use DA and I am always the first done with 100% on every math test. Smartest person is the one whose solution is the simplest and works.shortlilgirl02 likes this.