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

Objectives Goal Objectives Nursing students will demonstrate dosage calculations competency by passing a required dosage calculation test with a 90% or better. Objectives Students will understand how to correctly convert numbers between and within apothecaries, household, and metric measurement systems. Students will demonstrate ability to accurately calculate drug dosages

Dosage Calculation Test Must pass with a 90% or higher Three attempts allowed to pass You WILL NOT proceed in the program if you do not pass the dosage calculation exam MUST complete remediation exercises prior to second or third attempt May use testing center issued calculator for test (basic function calculator)

Testing in the Testing Center Must have CSI ID card or can’t get in You must be checked in 1 hour prior to testing center closing to receive test Identify test as following: Class – NURP 106 (Fundamentals) Instructor: Paula Hart Test: Dosage Calculation Exam # (1, 2 or 3)

Question- Why do we care about getting 100% on our dosage calculations test? Answer- Because a human being could die from a wrongly placed decimal point or an accidental extra zero placed during a dosage calculation… It’s that important. “3 babies died from the wrong dose of heparin given. Dosage calculation errors were made.” Indianapolis Star/ Sept 19, 2006

What do you need to be successful? Review the content in this power point, your text book, text book site, and Kaplan site Ask for help if you need it from your instructors, math lab, internet sites Use ALL available resources PRACTICE, PRACTICE, PRACTICE

Ready to begin?

Math Review – Roman Numerals Read from left to right A smaller numeral to the right of a larger numeral is added to the larger numeral A smaller numeral to the left of a larger numeral is subtracted from the larger numeral Easily translated to Arabic numbers

Roman Numeral Practice XXX = _________ XIV = __________ iii = ____________ XXV = ___________ XIX = ____________ VI = _____________ XXIV =___________

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

The Metric System The preferred system of measurement for prescribing and administering meds. Is a decimal system based on powers of 10 Base units are Grams- measures mass or weight, such as the dose of a drug Liters- measures the volume- such as the amount of a drug or solution to administer

Metric System cont. The order of the six metric units from largest to smallest can be remembered by: King Henry Died of a Disease Called Mumps (kilo-)(hecta-)(deka-)(base unit)(deci-)(centi-)(milli-) -gram -liter -meter Value to base: k-1000, h-100, d-10, base-1, d-0.1, c-0.01, m-0.001

Metric System cont Moving from one metric unit equivalent to the next involves moving the decimal point one place value to the left or right depending on whether you are moving up or down from the base. If you are moving from a smaller to a larger metric unit, such as mg to grams(gm) the decimal moves to the left. (Left = Larger) If your moving from larger to smaller, gm to mg, then move the decimal to the right.

Metric System cont Examples- To state 1 mg in gm you would move the decimal 3 place values to the left. So, 1 mg= 0.001 gm. To state 1 kg in gm you would move the decimal point 3 places to the right. So, 1 kg=1000 gm. Cubic centimeters (cc)=milliliters(ml) cc is no longer an acceptable abbreviation, however you will see it used. Convert within a system to make it easier to do calculations. Ex. 1000ml=1L

Apothecary and Household systems Common US systems of measurement but not used worldwide. Need to convert apothecary and household units of measurement into the metric system. Household conversions you need to memorize 1tsp=5ml 1Tbsp=3tsp 1 ounce=30ml 16ounces=1lb 2.2lb=1kg

Apothecary and Household systems cont. Apothecary measurements gr xv is 15 grains gr ii is 2 grains gr 1/6 is 1/6th of a grain Apothecary conversions you need to memorize gr i=60mg gr XV=1gm You will be provided with charts to help you with memorizing.

Apothecary and Household systems cont. Examples 2tsp=10ml (2tsp x 5ml=10ml) 8oz=240ml 100kg=220lb gr ¾=45mg

Calculating Dosages Three ways: Ratio & Proportion (solving for X) Dimensional Analysis (Preferred method) Formula We will be teaching Dimensional Analysis in this program. You may choose the method you are most comfortable with and use it consistently.

Calculating Dosages cont. We all learn differently. It very important that you identify the method that makes sense to you. If you don’t know which method makes sense, try out each method on the same set of practice problems and see which way makes sense. Once you find a method stick with it. Resist the temptation to “formula hop.” Whichever method you choose follow these 3 steps: 1.Convert 2. Think 3. Calculate Always ask yourself does my answer make sense. It is normal to feel nervous, so try to remember to “KISS” (Keep It Simple Students)

Ratio and Proportion: Dose on hand = What the Dr. ordered Solve for X Dose on hand = What the Dr. ordered volume/tablet X Example: The doctor orders 10 mg of a drug and you have 5 mg tabs on hand. You will give ____ tabs. 5mg = 10 mg 1 tab X tab 5X = 10 x 1 = 5X = 10 X = 2 Tablets

Dimensional Analysis: Set up units of measurement so that they cancel out, until you arrive at your correct measurement Always start with the dose ordered 10mg X 1 Tab = 10 Tab = 2 Tablets 1 5mg 5

Formula: Do conversions first, and then plug it into the equation to formulate the answer Dose ordered X Amount = Amount to Dose on hand on hand administer Ie: 10 mg X 1 Tab = 2 Tablets 5 mg

Conversion practice: 1 gram = _________ mg 1 cc = ___________mL 1 oz = ___________ mL 1 cc = ____________ mL 3 t = _____________ T 1 T = ____________ mL 1 t = _____________ mL

Conversion practice: 1 gram = ___________grains 60 mg = ____________ grains 1 kg = _____________ lbs 1 in = ______________ cm 120 mg = ____________ grains 0.5 gram = ____________ grains

Rounding Do not round until you get to the answer. You should always carry at least two decimal places (hundredths 0.01)throughout the problem. Answers must be rounded to the tenths (0.1) Follow the rules of rounding: if the number being rounded is from 1-4 then round down, 5-9 round up

Rounding cont Answers in drops (gtt) must be rounded to the nearest whole number. Capsules must be rounded to the nearest whole Enteric coated tablets must be rounded to the whole. Unscored tablets should be rounded to the whole. In other words, round to the nearest deliverable dose. Ex. If your answer is 1.9 suppositories or 21.7 gtts do these answers make sense?

Diluting tube feeding solutions Occasionally a client may not be able to tolerate full strength feeding solution. You may need to dilute a feeding solution to an ordered strength, such as ½ strength, 2/3 strength, etc. Formula to dilute a feeding solution Amount in can = Strength X 300ml = 3 X 4 300ml x 4 =3x 400ml-300=100ml 1200ml=x of water 3

General guidelines and tips when taking test Write everything you know at the top of your scratch paper at the start of the test. Identify the specific question being asked and then identify the components that will help you to arrive at the answer. Set up the equation carefully, label all units in the equation, make all conversions needed. Follow the rules of math for order of operations: multiply, divide, add and/or subtract

General guidelines and tips when taking test cont. Use your calculator, even if you think you can do it in your head. Follow guidelines for rounding. Show all your work. Recheck your answer when submitting it to the computer for keystroke errors. Don’t second guess yourself!!!

Practice Problem #1 The physician orders digoxin (Lanoxin) 5 mg. The pharmacy sends 15 mg/5mL. How many mL will you administer? 5mg x 5mL/15mg = 1.7mL

Practice Problem #2 The physician orders Mycostatin 250,000 units oral swish and swallow QID You have on hand: 100,000 units/mL How many mL will you administer? 250,000 units x mL/100,000 units= 2.5mL

Practice Problem #3 You have an order for gr (grain) X Acetaminophen (Tylenol) PO daily You have Tylenol 15 mg/mL How many mL will you administer? 10gr x 60mg/gr x mL/15mg= 40mL

Practice Problem #4 Your patient has just had lunch and you must calculate the total amount in mL consumed by the patient: 4 oz Juice 8 oz Milk 6 oz Broth 1oz=30mL so…. 120mL +240mL +180mL= 540mL

Practice Problem #5 The order is to start a continuous tube feeding of 2/3 strength Jevity at 50ml/hr. How much water will you add to the entire can to get the desired strength if each can contains 300ml? 300ml = 2 x 3 300ml x 3= 2x 900ml=x 2 450ml=x 450ml-300ml=150

Reconstitution Some medications are unstable when stored in solution or liquid form, therefore they are supplied as a powder. Before they can be administered they must be dissolved or “reconstituted” by mixing with a diluent (liquid) The volume of diluent used to dissolve the powder determines its unit concentration or the dose of drug contained in 1ml (mg/ml)

Reconstitution cont. Vials usually will have reconstituting directions printed on them so you must determine the type and amount of diluent to be added in order to reconstitute the drug correctly. The resulting solution strength or concentration (mg/ml) will be found in the instructions on the vial. The mg/ml is now the available dose of the drug ordered. Reconstitution ex pges 237-244

Dosages based on body weight Sometimes dosages are ordered by body weight of the pt., especially when giving pediatric doses. Remember all medication math is done in the metric system, so weight for dosages must be converted and calculated in kg. Remember 1lb=16oz, 1kg=2.2lb When converting from lbs to kg, divide by 2.2 When converting ounces to lbs divide by 16

Dosages based on body weight Ex. A baby weighs 10lb 12oz. How many lbs is this? First divide 12oz by 16= 0.75lb. So this baby weighs 10.75 lbs. Now how many kg does this baby weigh? 10.75/2.2=4.88kg (leave at 4.88 for calculations) Now we must multiply the ordered mg/kg dose by the weight of the pt in kg to get the desired dose for that pt. Then do your dosage calculations. Ex. Ordered drug is 2mg/kg, available is 10mg/ml, the baby weighs 10lb 12oz, how much will you give? Wt=4.88 kg 2mg/kg=9.8mg You will give 0.98ml or 1ml

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

Calculating IV flow rates IV flow rate is the speed at which the IV fluid infuses in the body. Usually measured in drops per minute (gtt/min) The number of gtts required to deliver 1mL of fluid varies with the type of administration set used. The administration set is made of plastic tubing, a drip chamber, and a “spike,” which is inserted into the bag/bottle of fluid/medication. There are 2 types of sets: Macrodrip=10,15,or 20 gtt/mL or Microdrip=60gtt/ml

Calculating Flow rates for IVs IV flow rate formula: Volume of infusion in mL x gtt factor = Flow rate time of infusion (usually in min) (usually in gtt/min) Ex: Administer D5 1/2NS at 30mL/hr using a microdrip. 30mL x 60gtt/mL =30gtt/min 60 min Administer 3,000mL D5 1/2NS in 24 hrs with a drop factor of 15gtt/mL 3000mL x 15gtt/mL = 31.25gtt/min 1440 min

Drugs Infusing in Less than 1 hour: If a drug is ordered to be infused in 1 hour or less what do you do? Example: Mandol 1 Gm in 50 mL NS Infuse in 30 minutes. Adm. Set: 15gtt/cc 50 mL x 15gtt/mL = 25gtt/min 30 min

Example: You have an order for Aldomet 250 mg IVPB in 100 mL D5W to be infused over 45 minutes. The administration set is labeled 10 gtt/mL What is the drop rate? 100 mL x 10gtt/mL = 22.22 or 22gtt/min 45 minutes

Practice Problems The nurse hangs 1 Liter D5W to infuse over 8 hours. The administration set is labeled 60 gtt/mL. What is the gtt/min? 1000 mL x 60gtt/ml =125gtt/min 480 min

Dosage Calculations The doctor orders 50 mL of Normal Saline (NS) to infuse over 30 minutes. Your tubing is labeled 15 gtt/mL. 50mL x 15gtt/mL = 25gtt/min 30 minutes

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

Looking to the future This semester we covered the basic knowledge of dosage calculations. Each semester the math test will add more advanced problem solving along with the basic concepts learned here. So….. Again ask for help if you need it and PRACTICE, PRACTICE, PRACTICE