Dimensional Analysis Dosage calculations

YES YOU CAN DO IT!Dimensional Analysis Dosage calculations

Mulholland Ch 1 4 and working on 5, after this move on to orders, labels, errors, oral dosages.1

Understand the learning components needed in order to perform dosage calculations.Apply dimensional analysis method when calculating dosages for medication administration.Outcomes

DA for med order calcs makes life easier2

FORMULA METHOD:

RATIO AND PROPORTION:LINEAR:250 mg : 1 tab :: 1.5 g : x tabs

FRACTIONAL:

Other methods:Disadvantages: Must remember the extra step of changing D and H to same unit of measurement. May have many steps and variables.

WE WILL NOT USE THESE METHODS, SO YOU CAN RELAX!!

Relax

ADVANTAGES:Organized and simple structureSet up in one step so all information is in one problemEasy to see if set up is incorrect

REQUIRED ELEMENTS:Need to anticipate what units your answer needs to be inWhat your given quantity is and what units need to be convertedConversion factors to convert given quantity and units into your desired answer units

Dimensional analysis method

What is being ordered?In simpler terms

What do we have on hand?

Do we need any equivalents, or do we need to convert into equivalents?

Where are we going, what are we looking for?

What is the doctor ordering or prescribing, 650 mg Tylenol PO q6h prn headache? 1 mg Dilaudid IV q3h prn moderate to severe pain? Lasix 20 mg PO bid ? Did u read p101 med freq, abbrev?Tylenol 325 mg tablets, or Dilaudid 2 mg / ml, or Lasix 40 mg tablets ?What if he ordered 0.65 g Tylenol ? Or drug x 5 mg per kg and pt wt in poundsWhat are you being asked to give? What unit are we being asked to give for the ordered dose? Are we looking for mL? mg? g,? Or tablets? We are looking for what is the DESIRED UNIT DOSE

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Determine the label you want your answer to be in (desired answer units) and write it on the right side of your equation. (your book also tells you to put desired answer units on the left side of your page, Mulholland, p.46) Put the known values (given quantity and units) of the problem in fraction form on the left side of your equation. Remember, the desired answer unit must be in the numerator. (Mulholland, p.47)Put in any conversion factors you will need to work towards the desired label.Cancel out all labels that are both in numerator and denominator.Do the math: reduce, multiply the numerators, multiply the denominators; then divide the numerator by the denominator.

Ideas to help you

Look at without fancy terminology Class can look at page 46 for book terminologyLABEL DESIRED ANSWER UNITS - How many hrs are in 3 days? What want to know? HOURSKNOWN VALUES GIVEN QTY UNITS What were we given to figure out? 3 daysCONVERSION FACTORS, What do we need to convert to get the answer? We know 1 day = 24 hrs 30 days / 1 x

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Basic math functions / FractionsAdding, Subtracting, Multiplication, DivisionDecimals -King Henry Doesn't [Usually] Drink Chocolate Milk with a MicroscopeThe first letters stand for the prefixes, with "Usually" in the middle standing for the "unit", being meters, grams, or liters. Many memory phrases omit the "Usually", and consequently students forget where the basic unit goes, messing up their conversions. Leave the "Usually" in there so you can keep things straight:kilo- hecto- deka- [unit] deci- centi- milli- ^- ^- micro-Must know equivalents / conversions (no apothecary items).Using Estimation (Mulholland, p.136) and Estimated Dose to anticipate your answer, then do your DA equation.

Things you will need to know

Using Estimation example of hours in 3 days, or 650 mg tylenol with 325 mg tabs, get idea of what answer is,Do exercises pages 137 150 in Mulholland. 2. Also, don't forget to tell them to ignore the apothecary items (which I think this book leaves out entirely or it might be in there, I can't remember).3. The book addresses "approximate equivalents" which is always confusing, maybe you could add something about that too.

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Lets not make this too complicated: We know that there are 72 hours in 3 days, this is how it would look using D.A. -Some things are common sense

Lets start with a conversion40 L = ______ gal? gal:

Desired Answer UnitsStarting (Conversion) Factor

gal

10Given Quantity and Units

110

CONVERSIONS NEED TO KNOW1 gallon = 4 Liters (according to Mulhollands approximate English conversions) but really is 3.785 L or 3.79If students bring up discrepancy, tell them re pg 66 & 81Household measurements10

Same problem different setup40 L = ______ gal

Desired Answer UnitsStarting (Conversion) Factor

galGiven Quantity and Units

11010

Give Aspirin 0.65 g PO q 4 h prn headache Bottle: 325 mg per tablet (1 tablet = 325 mg)How many tablets will you give per dose?Conversion factor: 1000 mg = 1 g

What are we looking to give?TabletsWhat is dose on hand?325 mg per tabletWhat is the ordered dose?0.65 g dose

How will we set this up using Dimensional Analysis?

Order:

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What are we looking for?What is dosage on hand?What is the conversion factor and what is the order? Work it

Mulholland, pg 115-116 for similar problem

Cancel out and do the math:Work it

So, you will give the patient 2 tablets as needed every 4 hrs

You have an order for Daypro 1200 mg po bid:

A simple example

21cap2

Mulholland, pg 138, problem 5 for similar problemDesired Answer Units

Mulholland, pg 14715

The order reads Estratab 3125 mcg po daily:

Another complex example

tab

Desired Answer Units2.5 tab

Order: Azithromycin 12 mg/kg PO daily dose. Patient weighs 22 lbs. Pharmacy sends a 240 mL bottle of Azithromycin labeled 200mg/5mL. How many mL will you pour for each dose?How about a more complex problem

Desired Answer UnitsMulholland, pg 160, 147 for similar problems

110

1

Mulholland, pg 180

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practiceYour patient may receive Dilaudid 3 mg IM q3h for pain. At this hospital Dilaudid is supplied in 1-ml ampules containing 4 mg. How many milliliters will you administer?

ml

0.75

Mulholland, J. M. (2011). The nurse, the math, the meds: Drug Calculations Using Dimensional Analysis. (2nd ed.). St Louis, MO: Elsevier Mosby.

Moore, S.G. (2011). Nursing math simplified: Math magic. (5th ed.). Clearwater, FL: H&H Publishing.

Horntvedt, T. (2012). Calculating Dosages Safely: A dimensional analysis approach. Philadelphia, PA: F.A. Davis.

Resources

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