DOSAGE CALCULATIONS Fundamentals of nursing pg 736-738 Medical Dosage Calculations Olsen, et al

DOSAGE DOSAGE CALCULATIONSCALCULATIONS

Fundamentals of nursing pg Fundamentals of nursing pg 736-738736-738

Medical Dosage Calculations Medical Dosage Calculations

Olsen, et al Olsen, et al

ObjectivesObjectives

GoalGoal Nursing students will demonstrate dosage Nursing students will demonstrate dosage

calculations competency by passing a calculations competency by passing a required dosage calculation test with a 90% required dosage calculation test with a 90% or better.or better.

ObjectivesObjectives Students will understand how to correctly Students will understand how to correctly

convert numbers between and within convert numbers between and within apothecaries, household, and metric apothecaries, household, and metric measurement systems.measurement systems.

Students will demonstrate ability to Students will demonstrate ability to accurately calculate drug dosagesaccurately calculate drug dosages

Dosage Calculation TestDosage Calculation Test

Must pass with a 90% or higherMust pass with a 90% or higher Three attempts allowed to passThree attempts allowed to pass You WILL NOT proceed in the program You WILL NOT proceed in the program

if you do not pass the dosage if you do not pass the dosage calculation examcalculation exam

MUST complete remediation exercises MUST complete remediation exercises prior to second or third attemptprior to second or third attempt

May use testing center issued calculator May use testing center issued calculator for test (basic function calculator)for test (basic function calculator)

Testing in the Testing Testing in the Testing CenterCenter

Must have CSI ID card or can’t get inMust have CSI ID card or can’t get in You must be checked in 1 hour prior to You must be checked in 1 hour prior to

testing center closing to receive testtesting center closing to receive test Identify test as following:Identify test as following:

Class – NURP 106 (Fundamentals)Class – NURP 106 (Fundamentals) Instructor: Paula HartInstructor: Paula Hart Test: Dosage Calculation Exam # (1, 2 or Test: Dosage Calculation Exam # (1, 2 or

3)3)

Question- Why do we care about getting Question- Why do we care about getting 100% on our dosage calculations test?100% on our dosage calculations test?

Answer- Because a human being could die Answer- Because a human being could die from a wrongly placed decimal point or an from a wrongly placed decimal point or an accidental extra zero placed during a accidental extra zero placed during a dosage calculation…dosage calculation…

It’s that important. It’s that important.

““3 babies died from the wrong dose of 3 babies died from the wrong dose of heparin given. Dosage calculation errors heparin given. Dosage calculation errors were made.”were made.”Indianapolis Star/ Sept 19, 2006Indianapolis Star/ Sept 19, 2006

What do you need to be What do you need to be successful?successful?

Review the content in this power Review the content in this power point, your text book, text book site, point, your text book, text book site, and Kaplan siteand Kaplan site

Ask for help if you need it from your Ask for help if you need it from your instructors, math lab, internet sitesinstructors, math lab, internet sites

Use ALL available resourcesUse ALL available resources PRACTICE, PRACTICE, PRACTICE PRACTICE, PRACTICE, PRACTICE

Ready to begin?Ready to begin?

Math Review – Roman Math Review – Roman NumeralsNumerals

Read from left to rightRead from left to right A smaller numeral to the right of a A smaller numeral to the right of a

larger numeral is added to the larger larger numeral is added to the larger numeralnumeral

A smaller numeral to the left of a A smaller numeral to the left of a larger numeral is subtracted from larger numeral is subtracted from the larger numeralthe larger numeral

Easily translated to Arabic numbersEasily translated to Arabic numbers

Roman Numeral PracticeRoman Numeral Practice

XXX = _________XXX = _________ XIV = __________XIV = __________ iii = ____________iii = ____________ XXV = ___________XXV = ___________ XIX = ____________XIX = ____________ VI = _____________VI = _____________ XXIV =___________XXIV =___________

Math Review contMath Review cont

You will need to review/refresh how You will need to review/refresh how to multiply and divide whole to multiply and divide whole numbers, fractions and decimals, numbers, fractions and decimals, how to convert minutes to hours, how to convert minutes to hours, and any basic arithmetic in your and any basic arithmetic in your Medical Dosage Calculations book.Medical Dosage Calculations book.

The Metric SystemThe Metric System

The preferred system of measurement The preferred system of measurement for prescribing and administering meds.for prescribing and administering meds.

Is a decimal system based on powers of Is a decimal system based on powers of 1010

Base units areBase units are Grams- measures mass or weight, such as Grams- measures mass or weight, such as

the dose of a drugthe dose of a drug Liters- measures the volume- such as the Liters- measures the volume- such as the

amount of a drug or solution to administeramount of a drug or solution to administer

Metric System cont.Metric System cont.

The order of the six metric units from The order of the six metric units from largest to smallest can be remembered by:largest to smallest can be remembered by:

KKing ing HHenry enry DDied of a ied of a DDisease isease CCalled alled MMumpsumps

(kilo-)(hecta-)(deka-)(base unit)(deci-)(centi-)(kilo-)(hecta-)(deka-)(base unit)(deci-)(centi-)(milli-)(milli-)

-gram -gram

-liter-liter

-meter-meterValue to base: k-1000, h-100, d-10, base-1, d-0.1, c-0.01, m-Value to base: k-1000, h-100, d-10, base-1, d-0.1, c-0.01, m-

0.0010.001

Metric System contMetric System cont Moving from one metric unit equivalent to Moving from one metric unit equivalent to

the next involves moving the decimal point the next involves moving the decimal point one place value to the left or right one place value to the left or right depending on whether you are moving up depending on whether you are moving up or down from the base.or down from the base.

If you are moving from a smaller to a If you are moving from a smaller to a larger metric unit, such as mg to larger metric unit, such as mg to grams(gm) the decimal moves to the left. grams(gm) the decimal moves to the left. ((LLeft = eft = LLarger)arger)

If your moving from larger to smaller, gm If your moving from larger to smaller, gm to mg, then move the decimal to the right.to mg, then move the decimal to the right.

Metric System contMetric System cont Examples- To state 1 mg in gm you Examples- To state 1 mg in gm you

would move the decimal 3 place values would move the decimal 3 place values to the left. So, 1 mg= 0.001 gm.to the left. So, 1 mg= 0.001 gm.

To state 1 kg in gm you would move the To state 1 kg in gm you would move the decimal point 3 places to the right. So, 1 decimal point 3 places to the right. So, 1 kg=1000 gm.kg=1000 gm.

Cubic centimeters (cc)=milliliters(ml)Cubic centimeters (cc)=milliliters(ml) cc is no longer an acceptable abbreviation, cc is no longer an acceptable abbreviation,

however you will see it used.however you will see it used. Convert within a system to make it Convert within a system to make it

easier to do calculations. Ex. 1000ml=1L easier to do calculations. Ex. 1000ml=1L

Apothecary and Apothecary and Household systemsHousehold systems

Common US systems of measurement but Common US systems of measurement but not used worldwide.not used worldwide.

Need to convert apothecary and household Need to convert apothecary and household units of measurement into the metric units of measurement into the metric system. system.

Household conversions you need to Household conversions you need to memorizememorize 1tsp=5ml1tsp=5ml 1Tbsp=3tsp1Tbsp=3tsp 1 ounce=30ml1 ounce=30ml 16ounces=1lb16ounces=1lb 2.2lb=1kg2.2lb=1kg

Apothecary and Apothecary and Household systems cont.Household systems cont.

Apothecary measurementsApothecary measurements gr xv is 15 grainsgr xv is 15 grains gr ii is 2 grainsgr ii is 2 grains gr 1/6 is 1/6gr 1/6 is 1/6thth of a grain of a grain

Apothecary conversions you need to Apothecary conversions you need to memorizememorize gr i=60mggr i=60mg gr XV=1gmgr XV=1gm

You will be provided with charts to help you You will be provided with charts to help you with memorizing.with memorizing.

Apothecary and Apothecary and Household systems cont.Household systems cont.

ExamplesExamples 2tsp=10ml (2tsp x 5ml=10ml)2tsp=10ml (2tsp x 5ml=10ml) 8oz=240ml8oz=240ml 100kg=220lb100kg=220lb gr ¾=45mggr ¾=45mg

Calculating DosagesCalculating Dosages Three ways:Three ways:

Ratio & Proportion (solving for X)Ratio & Proportion (solving for X) Dimensional Analysis (Preferred Dimensional Analysis (Preferred

method)method) FormulaFormula

We will be teaching Dimensional We will be teaching Dimensional Analysis in this program. Analysis in this program.

You may choose the method you are mostYou may choose the method you are most

comfortable with and use it consistently. comfortable with and use it consistently.

Calculating Dosages Calculating Dosages cont.cont.We all learn differently. It very important that you We all learn differently. It very important that you

identify the method that makes sense to you. If identify the method that makes sense to you. If you don’t know which method makes sense, try you don’t know which method makes sense, try out each method on the same set of practice out each method on the same set of practice problems and see which way makes sense. Once problems and see which way makes sense. Once you find a method stick with it. Resist the you find a method stick with it. Resist the temptation to “formula hop.”temptation to “formula hop.”

Whichever method you choose follow these 3 steps:Whichever method you choose follow these 3 steps:

1.Convert1.Convert

2. Think2. Think

3. Calculate3. Calculate

AlwaysAlways ask yourself does my answer make sense. ask yourself does my answer make sense.

It is normal to feel nervous, so try to remember to It is normal to feel nervous, so try to remember to “KISS” (“KISS” (KKeep eep IIt t SSimple imple SStudents)tudents)

Ratio and Proportion:Ratio and Proportion: Solve for XSolve for X Dose on handDose on hand == What the Dr. orderedWhat the Dr. ordered

volume/tablet Xvolume/tablet X

Example: The doctor orders 10 mg of a drug Example: The doctor orders 10 mg of a drug and you have 5 mg tabs on hand. You will give and you have 5 mg tabs on hand. You will give ____ tabs.____ tabs.

5mg5mg == 10 mg10 mg

1 tab X tab1 tab X tab 5X = 10 x 1 = 5X = 10 X = 2 Tablets5X = 10 x 1 = 5X = 10 X = 2 Tablets

Dimensional Analysis:Dimensional Analysis:

Set up units of measurement so that Set up units of measurement so that they cancel out, until you arrive at they cancel out, until you arrive at your correct measurementyour correct measurement

Always start with the dose orderedAlways start with the dose ordered

10mg10mg XX 1 Tab1 Tab == 10 Tab10 Tab == 2 2 TabletsTablets

1 5mg 5 1 5mg 5

Formula:Formula: Do conversions first, and then plug it into Do conversions first, and then plug it into

the equation to formulate the answerthe equation to formulate the answer

Dose orderedDose ordered X X Amount Amount == Amount to Amount to

Dose on hand on hand Dose on hand on hand administeradminister

Ie: Ie: 10 mg10 mg XX 1 Tab 1 Tab == 2 Tablets 2 Tablets

5 mg 5 mg

Conversion practice:Conversion practice:

1 gram = _________ mg1 gram = _________ mg 1 cc = ___________mL1 cc = ___________mL 1 oz = ___________ mL1 oz = ___________ mL 1 cc = ____________ mL1 cc = ____________ mL 3 t = _____________ T3 t = _____________ T 1 T = ____________ mL1 T = ____________ mL 1 t = _____________ mL1 t = _____________ mL

Conversion practice:Conversion practice:

1 gram = ___________grains1 gram = ___________grains 60 mg = ____________ grains60 mg = ____________ grains 1 kg = _____________ lbs1 kg = _____________ lbs 1 in = ______________ cm1 in = ______________ cm 120 mg = ____________ grains120 mg = ____________ grains 0.5 gram = ____________ grains0.5 gram = ____________ grains

RoundingRounding

Do not round until you get to the Do not round until you get to the answer. You should always carry at answer. You should always carry at least two decimal places (hundredths least two decimal places (hundredths 0.01)throughout the problem. 0.01)throughout the problem.

AnswersAnswers must be rounded to the must be rounded to the tenths (0.1)tenths (0.1)

Follow the rules of rounding: if the Follow the rules of rounding: if the number being rounded is from 1-4 number being rounded is from 1-4 then round down, 5-9 round upthen round down, 5-9 round up

Rounding contRounding cont Answers in drops (gtt) must be rounded to Answers in drops (gtt) must be rounded to

the nearest whole number.the nearest whole number. Capsules must be rounded to the nearest Capsules must be rounded to the nearest

wholewhole Enteric coated tablets must be rounded to Enteric coated tablets must be rounded to

the whole. the whole. Unscored tablets should be rounded to the Unscored tablets should be rounded to the

whole.whole.

In other words, round to the nearest In other words, round to the nearest deliverable dose. Ex. If your answer is 1.9 deliverable dose. Ex. If your answer is 1.9 suppositories or 21.7 gtts do these answers suppositories or 21.7 gtts do these answers make sense?make sense?

Diluting tube feeding Diluting tube feeding solutionssolutions Occasionally a client may not be able to Occasionally a client may not be able to

tolerate full strength feeding solution. You tolerate full strength feeding solution. You may need to dilute a feeding solution to an may need to dilute a feeding solution to an ordered strength, such as ½ strength, 2/3 ordered strength, such as ½ strength, 2/3 strength, etc. strength, etc.

Formula to dilute a feeding solution Formula to dilute a feeding solution Amount in can Amount in can = Strength X300ml = 3

X 4 300ml x 4 =3x 400ml-X 4 300ml x 4 =3x 400ml-300=100ml 300=100ml

1200ml1200ml=x of water=x of water

3 3

General guidelines and General guidelines and tips when taking test tips when taking test

Write everything you know at the top of Write everything you know at the top of your scratch paper at the start of the test. your scratch paper at the start of the test.

Identify the specific question being asked Identify the specific question being asked and then identify the components that and then identify the components that will help you to arrive at the answer.will help you to arrive at the answer.

Set up the equation carefully, label all Set up the equation carefully, label all units in the equation, make all units in the equation, make all conversions needed.conversions needed.

Follow the rules of math for order of Follow the rules of math for order of operations: multiply, divide, add and/or operations: multiply, divide, add and/or subtractsubtract

General guidelines and General guidelines and tips when taking test tips when taking test

cont.cont. Use your calculator, even if you Use your calculator, even if you

think you can do it in your head.think you can do it in your head. Follow guidelines for rounding.Follow guidelines for rounding. Show all your work.Show all your work. Recheck your answer when Recheck your answer when

submitting it to the computer for submitting it to the computer for keystroke errors. keystroke errors.

Don’t second guess yourself!!!Don’t second guess yourself!!!

Practice Problem #1Practice Problem #1

The physician orders digoxin The physician orders digoxin (Lanoxin) 5 mg.(Lanoxin) 5 mg.

The pharmacy sends 15 mg/5mL. The pharmacy sends 15 mg/5mL. How many mL will you administer? How many mL will you administer?

5mg x 5mg x 5mL/15mg = 1.7mL= 1.7mL


The physician orders Mycostatin The physician orders Mycostatin 250,000 units oral swish and swallow 250,000 units oral swish and swallow QIDQID

You have on hand: 100,000 units/mLYou have on hand: 100,000 units/mL

How many mL will you administer?How many mL will you administer?

250,000 units x mL/100,000 units= 250,000 units x mL/100,000 units= 2.5mL2.5mL


You have an order for gr (grain) X You have an order for gr (grain) X Acetaminophen (Tylenol) PO dailyAcetaminophen (Tylenol) PO daily

You have Tylenol 15 mg/mLYou have Tylenol 15 mg/mL

How many mL will you administer?How many mL will you administer?

10gr x 60mg/gr x mL/15mg= 40mL 10gr x 60mg/gr x mL/15mg= 40mL


Your patient has just had lunch and Your patient has just had lunch and you must calculate the total amount you must calculate the total amount in mL consumed by the patient:in mL consumed by the patient: 4 oz Juice4 oz Juice 8 oz Milk8 oz Milk 6 oz Broth 6 oz Broth

1oz=30mL so….1oz=30mL so….

120mL +240mL +180mL= 540mL120mL +240mL +180mL= 540mL

Practice Problem #5Practice Problem #5 The order is to start a continuous tube The order is to start a continuous tube

feeding of 2/3 strength Jevity at 50ml/hr. feeding of 2/3 strength Jevity at 50ml/hr. How much water will you add to the How much water will you add to the entire can to get the desired strength if entire can to get the desired strength if each can contains 300ml?each can contains 300ml?

300ml300ml = = 2 2

x 3x 3

300ml x 3= 2x300ml x 3= 2x

900ml=x=x

22

450ml=x 450ml-450ml=x 450ml-300ml=150300ml=150

Reconstitution Reconstitution Some medications are unstable when Some medications are unstable when

stored in solution or liquid form, stored in solution or liquid form, therefore they are supplied as a therefore they are supplied as a powder. powder.

Before they can be administered they Before they can be administered they must be dissolved or “reconstituted” must be dissolved or “reconstituted” by mixing with a diluent (liquid)by mixing with a diluent (liquid)

The volume of diluent used to The volume of diluent used to dissolve the powder determines its dissolve the powder determines its unit concentration or the dose of unit concentration or the dose of drug contained in 1ml (mg/ml)drug contained in 1ml (mg/ml)

Reconstitution cont.Reconstitution cont.

Vials usually will have reconstituting Vials usually will have reconstituting directions printed on them so you must directions printed on them so you must determine the type and amount of determine the type and amount of diluent to be added in order to diluent to be added in order to reconstitute the drug correctly.reconstitute the drug correctly.

The resulting solution strength or The resulting solution strength or concentration (mg/ml) will be found in concentration (mg/ml) will be found in the instructions on the vial. The mg/ml the instructions on the vial. The mg/ml is now the available dose of the drug is now the available dose of the drug ordered. ordered.

Reconstitution ex pges 237-244Reconstitution ex pges 237-244

Dosages based on body Dosages based on body weightweight

Sometimes dosages are ordered by body Sometimes dosages are ordered by body weight of the pt., especially when giving weight of the pt., especially when giving pediatric doses.pediatric doses.

Remember all medication math is done in Remember all medication math is done in the metric system, so weight for dosages the metric system, so weight for dosages must be converted and calculated in kg.must be converted and calculated in kg.

Remember 1lb=16oz, 1kg=2.2lbRemember 1lb=16oz, 1kg=2.2lb When converting from lbs to kg, divide by When converting from lbs to kg, divide by

2.22.2 When converting ounces to lbs divide by 16When converting ounces to lbs divide by 16

Dosages based on body Dosages based on body weightweight Ex. A baby weighs 10lb 12oz. How many lbs is Ex. A baby weighs 10lb 12oz. How many lbs is

this? First divide 12oz by 16= 0.75lb. So this this? First divide 12oz by 16= 0.75lb. So this baby weighs 10.75 lbs. Now how many kg does baby weighs 10.75 lbs. Now how many kg does this baby weigh? 10.75/2.2=4.88kg (leave at 4.88 this baby weigh? 10.75/2.2=4.88kg (leave at 4.88 for calculations)for calculations)

Now we must multiply the ordered mg/kg dose by Now we must multiply the ordered mg/kg dose by the weight of the pt in kg to get the desired dose the weight of the pt in kg to get the desired dose for that pt. Then do your dosage calculations.for that pt. Then do your dosage calculations.

Ex. Ordered drug is 2mg/kg, available is Ex. Ordered drug is 2mg/kg, available is 10mg/ml, the baby weighs 10lb 12oz, how much 10mg/ml, the baby weighs 10lb 12oz, how much will you give? will you give? Wt=4.88 kgWt=4.88 kg 2mg/kg=9.8mg2mg/kg=9.8mg You will give 0.98ml or 1mlYou will give 0.98ml or 1ml

Practice problemPractice problem

You have an order for cefaclor You have an order for cefaclor (Ceclor) 20 mg/kg/day in three (Ceclor) 20 mg/kg/day in three divided doses. The child weighs 20 divided doses. The child weighs 20 lbs. How much will you give in each lbs. How much will you give in each dose?dose? Wt=9.09Wt=9.09 Daily dose=181.8Daily dose=181.8 Each dose=60.6Each dose=60.6

Calculating IV flow ratesCalculating IV flow rates IV flow rate is the speed at which the IV fluid IV flow rate is the speed at which the IV fluid

infuses in the body.infuses in the body. Usually measured in drops per minute (gtt/min)Usually measured in drops per minute (gtt/min) The number of gtts required to deliver 1mL of The number of gtts required to deliver 1mL of

fluid varies with the type of administration set fluid varies with the type of administration set used. used.

The administration set is made of plastic tubing, The administration set is made of plastic tubing, a drip chamber, and a “spike,” which is inserted a drip chamber, and a “spike,” which is inserted into the bag/bottle of fluid/medication.into the bag/bottle of fluid/medication.

There are 2 types of sets: Macrodrip=10,15,or There are 2 types of sets: Macrodrip=10,15,or 20 gtt/mL or Microdrip=60gtt/ml20 gtt/mL or Microdrip=60gtt/ml

Calculating Flow rates Calculating Flow rates for IVsfor IVs IV flow rate formula:IV flow rate formula:

Volume of infusion in mL x gtt factor Volume of infusion in mL x gtt factor = Flow rate

time of infusion (usually in min) (usually time of infusion (usually in min) (usually inin

gtt/min)gtt/min)

Ex: Administer D5 1/2NS at 30mL/hr using a Ex: Administer D5 1/2NS at 30mL/hr using a microdrip.microdrip.

30mL x 60gtt/mL 30mL x 60gtt/mL =30gtt/min =30gtt/min

60 min60 min

Administer 3,000mL D5 1/2NS in 24 hrs with a Administer 3,000mL D5 1/2NS in 24 hrs with a drop factor of 15gtt/mLdrop factor of 15gtt/mL

3000mL x 15gtt/mL = 31.25gtt/min = 31.25gtt/min

1440 min1440 min

Drugs Infusing in Less than Drugs Infusing in Less than 1 hour:1 hour:

If a drug is ordered to be infused in If a drug is ordered to be infused in 1 hour or less what do you do?1 hour or less what do you do?

Example: Mandol 1 Gm in 50 mL NSExample: Mandol 1 Gm in 50 mL NSInfuse in 30 minutes. Adm. Set: Infuse in 30 minutes. Adm. Set:

15gtt/cc15gtt/cc

50 mL x 15gtt/mL50 mL x 15gtt/mL = 25gtt/min= 25gtt/min

30 min30 min

Example:Example:

You have an order for Aldomet 250 mg You have an order for Aldomet 250 mg IVPB in 100 mL D5W to be infused over IVPB in 100 mL D5W to be infused over 45 minutes. The administration set is 45 minutes. The administration set is labeled 10 gtt/mLlabeled 10 gtt/mL

What is the drop rate?What is the drop rate?

100 mL x 10gtt/mL = 22.22 or = 22.22 or 22gtt/min22gtt/min

45 minutes45 minutes

Practice ProblemsPractice Problems

The nurse hangs 1 Liter D5W to The nurse hangs 1 Liter D5W to infuse over 8 hours. The infuse over 8 hours. The administration set is labeled 60 administration set is labeled 60 gtt/mL.gtt/mL.

What is the gtt/min? What is the gtt/min?

1000 mL x 60gtt/ml =125gtt/min=125gtt/min

480 min480 min

Dosage CalculationsDosage Calculations

The doctor orders 50 mL of Normal The doctor orders 50 mL of Normal Saline (NS) to infuse over 30 Saline (NS) to infuse over 30 minutes. Your tubing is labeled 15 minutes. Your tubing is labeled 15 gtt/mL.gtt/mL.

50mL x 15gtt/mL50mL x 15gtt/mL = 25gtt/min = 25gtt/min

30 minutes30 minutes

Do you now feel better about your Do you now feel better about your knowledge of dosage calculations? Well, knowledge of dosage calculations? Well, you should. you should.

Looking to the futureLooking to the future

This semester we covered the basic This semester we covered the basic knowledge of dosage calculations. knowledge of dosage calculations. Each semester the math test will add Each semester the math test will add more advanced problem solving more advanced problem solving along with the basic concepts along with the basic concepts learned here. learned here.

So….. Again ask for help if you need So….. Again ask for help if you need it and it and

PRACTICE, PRACTICE, PRACTICEPRACTICE, PRACTICE, PRACTICE

Documents

DOSAGE CALCULATIONS Fundamentals of nursing pg 736-738 Medical Dosage Calculations Olsen, et al