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# Med Math

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### Transcript

• 1. Med Math
• 2. Tips for success
• Pick one method, that is easiest for YOU
• Study it
• Learn it
• Practice it
• Practice it
• Practice it
• 3. Topics
• Apothecary System
• Weight and Temperature Conversions
• Metric System
• Med Math
• Weight Based Doses
• Drip Rate Calculations
• 4. 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
• 5. Weight Conversion
• Fact: 1 kilogram (kg) = 2.2 pounds (lbs)
• Fact: Weight in kgs X 2.2 = weight in pounds
• 6. Conversion Practice
• 80 kilogram patient, what is weight in pounds
• kilograms X 2.2 = pounds
80 X 2.2 = 176 lbs .
• 7. Conversion Practice
• 100 kilogram patient, what is weight in pounds
• kilograms X 2.2 = pounds
100 X 2.2 = 220 lbs.
• 8. 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
• 9. Conversion Practice
• 245 lb patient, what is weight in kilograms
• lbs / 2.2 = kilograms
245 / 2.2 = 111.36 kgs
• 10. Conversion Practice
• 140 lb patient, what is the weight in kilograms
• lbs / 2.2 = kilograms
140 / 2.2 = 63.63 kilograms
• 11. Conversion Practice
• The easy way…
• Half of weight in pounds, subtract 10%
• Example: 180 lbs . . . . . 90
10% of 90 = 9 81 kilograms
• 12. Conversion Practice
• 180 lb patient, what is the weight in kilograms
• lbs / 2.2 = kilograms
• 180 / 2.2 = 81.82 kilograms
• 13. KNOW YOUR WEIGHT CONVERSIONS!!!!!
• 14. Temperature Conversions
• Fahrenheit:
• Water Freezes at 32 º F
• Water Boils at 212º F
• Celsuis:
• Water Freezes at 0 º C
• Water Boils at 100º C
• 15. 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 = 37 º C
• 16. Practice
• Convert 103 º F to Celsius
• 103 – 32 = 71
71 X 0.556 = 39.48 º C
• 17. Temperature Conversions
• Celsius  Fahrenheit
• Multiply by 1.8
• 37 º X 1.8 = 66.6
• 66.6 + 32 = 96.6º F
• 18. Practice
• Convert 44 º C to Fahrenheit
• 44 X 1.8 = 79.2
• 79.2 + 32 = 111.2 º F
• 120 º F  Celsius
• 76.4 º F  Celsuis
• 60 º C  Fahrenheit
• 24 º C  Fahrenheit
• 20. Metric System
• System of 10 (base 10)
• No fractions only decimals
• EASY!
• 21. Metric System
• 22. Metric System
• Deca 10
• Hecto 100
• Kilo 1000
• Deci 0.1
• Centi 0.01
• Mili 0.001
• 23. Metric System
• Gram = g
• Liter = l
• Kilogram = kg
• Milliliter = mL
• Milligram = mg
• Cubic centimeter = cc
• Microgram =  g
• 1 L = 1000 mL
• 1 mL = 1 cc
• 1 g = 1000 mg
• 1 mg = 1000  g
• 1cc = 1 mL
• 1  g = 0.001 mg
• 1 mg = 0.001 g
• 24. 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
• 4.3795
• + 5.2389
• ---------------
• 9.6184
• 26. Subtraction
• 9.6184
• - 5.2389
• ---------------
• 4.3795
• 27. Multiplication
• 34.76
• X 4.935
• --------------
• 17154060
• Add decimal places = 5
• 171.54060 = 171.5406
• 28. Division
• .75 / .995
• 75 / 99.5  move decimal
• --------------
• 0.7537
• 29. Converting
• 1g = 1000mg so… g  mg X 1000
• 1mg = 1000 µg so… mg   g X 1000
• 1g = ????  g = 1,000,000  g
• 30. Converting
• 500mL = 0.5L so… mL  L / 1000
• The Bottom Line…
• To convert from the base to mili X 1000
• To convert from mili to the base / 1000
• To convert from mili to  X 1000
• To convert from base to  X 1000000
• The long formula
• dose desired X volume on hand
• Volume to administer = ------------------------------------
• dose on hand
• 32. Example
• Orders call for 0.5mg Atropine for symptomatic bradycardia. You have 1mg in 10 mL pre-filled syringe
• 0.5 mg X 10 mL
• ------------------ = volume to administer
• 1.0 mg
• 33. Example
• mg’s cancel out
• 0.5 X 10mL = 5mL
• 0.5 mg X 10 mL
• ------------------ = 5 mL
• 1.0 mg
• 34. Another Example
• You have 100mg Furosemide in a 10mL vial. The order is for 40mg
• 80 mg X 10 mL
• ------------------ = volume to administer
• 100 mg
• 35. Example
• mg’s cancel out
• 80 X 10mL = 800mL/100 = 8
• 80 mg X 10 mL
• ------------------ = 8 mL
• 100 mg
• 36. Catching on?
• 37. Try it on your own
• Benadryl – 50 mg in 2 mL
• Orders are for 12.5 mg
• 12.5 mg X 2 mL
• ------------------ = volume to administer
• 50 mg
• 12.5 X 2 = 25 / 50 = 0.5 mL
• 39. The easy way
• Set up an equation
• Cross Multiply
• Divide
• Sound like algebra?
• 40. The easy way
• Order is for 45 mg Benadryl
• You have 50 mg in 2 mL
• 50 45
• --- ---
• 2 X
• 41. The easy way
• 50 45
• --- ---
• 2 X
• Multiply 45 X 2 = 90
• Divide 90 by 50 = 1.8
• So… you would administer 1.8 mL = 45 mg
• 42. Another example
• Order is for 3 mg Valium
• You have 10 mg in 2 mL
• 10 3
• --- --
• 2 X
• 43. Another example
• 10 3
• --- --
• 2 X
• Multiply 3 X 2 = 6
• Divide 6 by 10 = 0.6
• So… you would administer 0.6 mL = 3 mg
• 44. Finally, the good stuff
• Order is for 145 µ g of Fentanyl Citrate
• You have 300 mcg in 5 mL
• 300 145
• ----- -----
• 5 X
• 45. The good stuff
• 300 145
• ----- -----
• 5 X
• Multiply 145 X 5 = 725
• Divide 735 by 300 = 2.42 = 2.4
• So… you would administer 2.4 mL = 145 mg
• 46. Weight Based Dosage
• Convert weight to kgs.
• Calculate the dose to give
• Calculate the volume to administer
• 47. 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
• 48. 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
• 49. 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
• 50. Weight Based Dosage
• 126 mg X 20 mL
• ------------------ = volume to administer
• 200 mg
126 X 20 = 2520 / 200 = 12.6 mL So, one complete syringe containing 10 mL plus approx. 2.6 mL from a second syringe
• 51. Weight Based Dosage
• Pediatric
• 2mg/kg Benadryl for a 25 lb patient
• Convert weight to kilograms
• 25 / 2.2 = 11.36 kgs
• Or
• 12.5 – 1.2 = 11.3 kgs
• 52. Weight Based Dosage
• Pediatric
• 2mg/kg Benadryl for a 25 lb patient
• 2. Calculate the dose to give
• 11.3 kgs X 2 mg/kg = 22.6 mg
• 53. Weight Based Dosage
• Pediatric
• 2mg/kg Benadryl for a 25 lb patient
• 3. Calculate the volume to administer
• 22.6 mg X 1 mL
• -------------------- = 0.45 mL
• 50 mg
• 54. 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
• 55. Or the easy way
• 50 22
• --- ---
• 1 X
• 22 X 1 = 22 / 50 = 0.44 mL
• 56. 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
• 57. Microdrips
• 60 gtts = 1 mL
• If your dose was 1 mL / hr what would your drip rate be?
• 1 gtt / minute
• Why?
• 60 gtts = 1 mL (our dose)
• 1 drop / min = 60 gtts/hr = 1 mL = 60 gtts
• 58. Easy huh?
• 59. 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
• 60. 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
• 61. Dose not in mL/hr or mL/min?
• 62. No sweat…
• 63. Understanding Concentration of 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
• 64. Drug in fluid
• 800 mg X mg
• ---------- --------
• 1000 mL 1 mL
• 800 X 1 = 800 / 1000 = 0.8 mg/mL
• 65. Drug in fluid
• 400 mg X mg
• ---------- --------
• 250 mL 1 mL
• 400 X 1 = 400 / 250 = 1.6 mg / mL
• Convert mg  mcg  Dopamine
• 1.6 X 1000 = 1600 mcg / mL
• 66. You do it
• You add 1 gram of Lidocaine to 250 mL NS
• The answer should be in mg/mL
Survey Says…. 1 gm = 1000 mg 1000 mg in 250 mL = 4mg/mL
• 67. Not mL/hr but mg/min
• Lidocaine 2mg/min
• Mixed 1gm/250ml
1000mg = 1gm 1000mg/250ml = 4mg/ml Drip rate = 30gtts/min
• 68. Why?
• 4mg/ml
• The dose is 2mg/min
• Using a microdrip (60) 60gtts=1ml
• 4mg/min = 60
• 2mg/min = 30
• 1mg/min = 15
• 69. 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
• 70.
• 2mg/min X 60 gtts/ml
• --------------------------
• 4mg/ml X 1min
2 X 60 120 -------- = --- 4 X 1 4 30 gtts
• 71. Putting it ALL together
• 72. Dopamine
• Weight Based
• Over time (mcg/kg/min)
• 73. 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
• 74.
• Convert Weight from lbs to kgs
• Convert measurements (mgs  µg)
• Determine µg/mL
• Formula
• 75. Step 1: Convert Weight
• 220 lbs  kgs
• 220 / 2.2 = 100 kgs
• 76. Step 2: Convert Measurements
• 800 mg  µg
• Mg  µg = X 1000
• 800,000 µg
• 77. Step 3: Determine µg/mL
• 800,000 µg / 500 mL
• 1600 µ / mL
• 78. Step 4: Formula
• Drug order ( µg/kg) X weight (kgs) X drip rate
• ---------------------------------------------------
• Concentration on hand (µg/ml) X time (min)
• 79. 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
• 80. 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
• 81. Step 1: Convert Weight
• 175 lbs / 2.2 = 79.5 ~ 79 kgs
• 87.5 – 8.7 = 78.8 ~ 79 kgs
• 82. Step 2: Convert Measurements
• 800 mg  µg
• 800,000 µg
• 83. Step 3: Determine µg/mL
• 800,000 mcg / 500 mL
• 1600 mcg / mL
• 84. 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
• 85. Step 4: Formula
• 5 X 79 X 60 = 23700
• 23700 / 1600 = 14.81 ~ 15 gtts/min
• 86. 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