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# Medmath pharmacology

## on Dec 01, 2011

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Nursing Pharmacology

Nursing Pharmacology

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## Medmath pharmacologyPresentation Transcript

• Med MathMakiNg Nurses’ Lives Simple in Numbers Dr. Cyruz P. Tuppal RN, RM, RT, MSN, MASPED, DMS, DNSc drcyruztuppal@gmail.com drcyruztuppal@yahoo.com
• Tips for success Pick one method, that is easiest for YOU Study it Learn it Practice it Practice it Practice it
• Topics Apothecary System Weight and Temperature Conversions Metric System Med Math  Administration Doses  Weight Based Doses  Drip Rate Calculations
• Apothecary System Phased out and replaced by metric system Basic Units: grain (gr), dram (dr), drop (gtt), ounce, (oz), pint (pt), quart (qt) Equivalents 1dr = 1 tsp = 60 gtts 3tsp = 1 Tbsp
• Weight Conversion Fact: 1 kilogram (kg) = 2.2 pounds (lbs) Fact: Weight in kgs X 2.2 = weight in pounds
• Conversion Practice 80 kilogram patient, what is weight in pounds kilograms X 2.2 = pounds 80 X 2.2 = 176 lbs.
• Conversion Practice 100 kilogram patient, what is weight in pounds kilograms X 2.2 = pounds 100 X 2.2 = 220 lbs.
• Weight Conversion Fact: 1 kilogram (kg) = 2.2 pounds (lbs) Fact: Weight in kgs X 2.2 = weight in pounds Fact: Weight in pounds / 2.2 = weight in kilograms
• Conversion Practice 245 lb patient, what is weight in kilograms lbs / 2.2 = kilograms 245 / 2.2 = 111.36 kgs
• Conversion Practice 140 lb patient, what is the weight in kilograms lbs / 2.2 = kilograms 140 / 2.2 = 63.63 kilograms
• Conversion Practice The easy way…Half of weight in pounds, subtract 10%Example: 180 lbs . . . . . 90 10% of 90 = 9 81 kilograms
• Conversion Practice 180 lb patient, what is the weight in kilograms lbs / 2.2 = kilograms 180 / 2.2 = 81.82 kilograms
• Temperature Conversions Fahrenheit:  Water Freezes at 32º F  Water Boils at 212º F Celsuis:  Water Freezes at 0º C  Water Boils at 100º C
• Temperature Conversions Fahrenheit  Celsius Subtract 32 from the temperature Multiply by 0.556 or 5/9 98.6 – 32 = 66.6 66.6 X 0.556 = 37.03 = 37º C
• Practice Convert 103º F to Celsius 103 – 32 = 71 71 X 0.556 = 39.48º C
• Temperature Conversions Celsius  Fahrenheit Multiply by 1.8 Add 32 37º X 1.8 = 66.6 66.6 + 32 = 96.6º F
• Practice Convert 44º C to Fahrenheit 44 X 1.8 = 79.2 79.2 + 32 = 111.2 º F
• On your own 120 º F  Celsius 76.4 º F  Celsuis 60 º C  Fahrenheit 24 º C  Fahrenheit
• Metric System System of 10 (base 10) No fractions only decimals EASY!
• Metric System
• Metric System Deca 10 Deci 0.1 Hecto 100 Centi 0.01 Kilo 1000 Mili 0.001
• Metric System Gram = g 1 L = 1000 mL Liter = l 1 mL = 1 cc Kilogram = kg 1 g = 1000 mg Milliliter = mL 1 mg = 1000 g Milligram = mg 1cc = 1 mL Cubic centimeter = 1 g = 0.001 mg cc 1 mg = 0.001 g Microgram = g
• The math Adding – keep the decimal points in line Subtracting – see above Multiplying – multiply without regard to decimals then add decimal places Dividing – make the divisor a whole number and add zeroes to the dividend
• Addition 4.3795 + 5.2389 --------------- 9.6184
• Subtraction 9.6184 - 5.2389 --------------- 4.3795
• Multiplication 34.76 X 4.935 -------------- 17154060Add decimal places = 5 171.54060 = 171.5406
• Division .75 / .995 75 / 99.5  move decimal -------------- 0.7537
• Converting1g = 1000mg so… g  mg X 10001mg = 1000 µg so… mg  g X 10001g = ???? g = 1,000,000 g
• Converting 500mL = 0.5L so… mL  L / 1000 The Bottom Line…To convert from the base to mili X 1000To convert from mili to the base / 1000To convert from mili to X 1000To convert from base to X 1000000
• Standard Administration The long formula dose desired X volume on hand Volume to administer = ------------------------------------ dose on hand
• Example Orders call for 0.5mg Atropine for symptomatic bradycardia. You have 1mg in 10 mL pre-filled syringe0.5 mg X 10 mL------------------ = volume to administer 1.0 mg
• Example mg’s cancel out 0.5 X 10mL = 5mL0.5 mg X 10 mL------------------ = 5 mL 1.0 mg
• Another Example You have 100mg Furosemide in a 10mL vial. The order is for 40mg80 mg X 10 mL------------------ = volume to administer 100 mg
• Example mg’s cancel out 80 X 10mL = 800mL/100 = 880 mg X 10 mL------------------ = 8 mL 100 mg
• Catching on?
• Try it on your own Benadryl – 50 mg in 2 mL Orders are for 12.5 mg Show your work
• Benadryl12.5 mg X 2 mL------------------ = volume to administer 50 mg12.5 X 2 = 25 / 50 = 0.5 mL
• The easy way Set up an equation Cross Multiply Divide Sound like algebra?
• The easy way Order is for 45 mg Benadryl You have 50 mg in 2 mL 50 45 --- --- 2 X
• The easy way 50 45 --- --- 2 XMultiply 45 X 2 = 90Divide 90 by 50 = 1.8So… you would administer 1.8 mL = 45 mg
• Another example Order is for 3 mg Valium You have 10 mg in 2 mL 10 3 --- -- 2 X
• Another example 10 3 --- -- 2 XMultiply 3 X 2 = 6Divide 6 by 10 = 0.6So… you would administer 0.6 mL = 3 mg
• Finally, the good stuff Order is for 145 µg of Fentanyl Citrate You have 300 mcg in 5 mL 300 145 ----- ----- 5 X
• The good stuff 300 145 ----- ----- 5 XMultiply 145 X 5 = 725Divide 735 by 300 = 2.42 = 2.4So… you would administer 2.4 mL = 145 mg
• Weight Based Dosage1. Convert weight to kgs.2. Calculate the dose to give3. Calculate the volume to administer
• Weight Based Dosage 1.5 mg/kg Lidocaine for a 185 lb patient in cardiac arrest.1. Convert the weight to kilograms.  185 / 2.2 = 84 kgs Or  93 – 9.3 = 83.7 = 84 kgs
• Weight Based Dosage 1.5 mg/kg Lidocaine for a 185 lb patient in cardiac arrest.2. Calculate the dose to give  84 kgs X 1.5 mg = 126 mg
• Weight Based Dosage 1.5 mg/kg Lidocaine for a 185 lb patient in cardiac arrest.3. Calculate the volume to administer  126 mg is the dose we want to give  10 mL pre-filled syringe containing 100 mg
• Weight Based Dosage 126 mg X 20 mL ------------------ = volume to administer 200 mg 126 X 20 = 2520 / 200 = 12.6 mLSo, one complete syringe containing 10 mL plus approx. 2.6 mLfrom a second syringe
• Weight Based Dosage Pediatric 2mg/kg Benadryl for a 25 lb patient1. Convert weight to kilograms  25 / 2.2 = 11.36 kgs Or  12.5 – 1.2 = 11.3 kgs
• Weight Based Dosage Pediatric 2mg/kg Benadryl for a 25 lb patient2. Calculate the dose to give  11.3 kgs X 2 mg/kg = 22.6 mg
• Weight Based Dosage Pediatric 2mg/kg Benadryl for a 25 lb patient3. Calculate the volume to administer 22.6 mg X 1 mL -------------------- = 0.45 mL 50 mg
• Or the easy way We know we want 2mg/kg The child ways 11.3 or roughly 11 kgs The dose will be 22mg 50 22 --- --- 1 X
• Or the easy way 50 22 --- --- 1 X22 X 1 = 22 / 50 = 0.44 mL
• Drip Rate Calculations Facts:  In a 60 drop set, 60 drops = 1 mL  In a 10 drop set, 10 drops = 1 mL  In a 15 drop set, 15 drops = 1 mL  Medications are usually given in 60 gtt sets  Doesn’t mean you cannot give it in a 10 gtt set  A 60 drip set is usually called a microdrip  A 10 drip set is usually called a macrodrip
• Microdrips 60 gtts = 1 mL If your dose was 1 mL / hr what would your drip rate be? 1 gtt / minuteWhy? 60 gtts = 1 mL (our dose) 1 drop / min = 60 gtts/hr = 1 mL = 60 gtts
• Easy huh?
• Let’s try another Using a 60 drop set, the dose is 30 mL/hr 60 gtts = 1 mL 30 mL = 1800 gtts 1800 gtts/60 min = 30 gtts/min
• And another Using a 60 drop set, the dose is 45 mL/hr 60 gtts = 1 mL 45 mL = 2700 gtts 2700 gtts / 60 min = 45 gtts / hr
• Dose not in mL/hr or mL/min?
• No sweat…
• Understanding Concentrationof drug in fluid A liter bag of fluid = 1000 cc or 1000 mL If you add 800 mg of a drug to 1000 mL of fluid, what would ur ratio of drug to fluid be? 800 mg X mg ---------- -------- 1000 mL 1 mL
• Drug in fluid 800 mg X mg ---------- -------- 1000 mL 1 mL800 X 1 = 800 / 1000 = 0.8 mg/mL
• Drug in fluid 400 mg X mg ---------- -------- 250 mL 1 mL400 X 1 = 400 / 250 = 1.6 mg / mLConvert mg  mcg  Dopamine1.6 X 1000 = 1600 mcg / mL
• You do it You add 1 gram of Lidocaine to 250 mL NS The answer should be in mg/mLSurvey Says…. 1 gm = 1000 mg 1000 mg in 250 mL = 4mg/mL
• Not mL/hr but mg/min Lidocaine 2mg/min Mixed 1gm/250ml 1000mg = 1gm 1000mg/250ml = 4mg/ml Drip rate = 30gtts/min
• Why? 4mg/ml The dose is 2mg/min Using a microdrip (60) 60gtts=1ml 4mg/min = 60 2mg/min = 30 1mg/min = 15
• The Math Drug order (mg/min) X IV Drip rate (gtts/ml) ------------------------------------------- Drug concentration (mg/ml) X 1min 2mg/min X 60 gtts/ml -------------------------- 4mg/ml X 1min
• 2mg/min X 60 gtts/ml-------------------------- 4mg/ml X 1min 2 X 60 120 -------- = --- 30 gtts 4X1 4
• Putting it ALL together
• Dopamine Weight Based Over time (mcg/kg/min)
• Weight based over time Order is for 7mcg/kg/min Drug on hand is 800 mg Drip Set is 60gtts/ml Pt weight is 220 lbs IV solution 500mL NS
• 1. Convert Weight from lbs to kgs2. Convert measurements (mgs  µg)3. Determine µg/mL4. Formula
• Step 1: Convert Weight 220 lbs  kgs 220 / 2.2 = 100 kgs
• Step 2: ConvertMeasurements 800 mg  µg Mg  µg = X 1000 800,000 µg
• Step 3: Determine µg/mL 800,000 µg / 500 mL 1600 µ / mL
• Step 4: FormulaDrug order (µg/kg) X weight (kgs) X drip rate---------------------------------------------------Concentration on hand (µg/ml) X time (min)
• Step 4: Formula 7 µg/kg X 100 kgs X 60 gtts/mL --------------------------------------- 1600 µg/mL X 1 min 7 X 100 = 700 X 60 = 4200 4200 / 1600 = 26.25 = 26 gtts/min
• Another Order is for 5 µg/kg/min Drug on hand is 800 mg = 800,000 µg 60 Drop set Pt weighs 175 lbs IV solution 500 mL NS
• Step 1: Convert Weight 175 lbs / 2.2 = 79.5 ~ 79 kgs 87.5 – 8.7 = 78.8 ~ 79 kgs
• Step 2: ConvertMeasurements 800 mg  µg 800,000 µg
• Step 3: Determine µg/mL 800,000 mcg / 500 mL 1600 mcg / mL
• Step 4: Formula Drug order X weight X drip rate --------------------------------------- Conc on hand X time 5 mcg/kg X 79 kgs X 60 ----------------------------- 1600 mcg/mL X 1 min
• Step 4: Formula 5 X 79 X 60 = 23700 23700 / 1600 = 14.81 ~ 15 gtts/min
• An easy check to your work For 5 µg / kg / min Take weight in pounds (175) Drop the last digit (17) Subtract 1 (16)  in the ballpark, not completely accurate