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Math and Dosage Calculations for Health Care Third Edition Booth & Whaley

Math and Dosage Calculations for Health Care Third Edition Booth & Whaley. Chapter 12: Specialized Calculations. Learning Outcomes. 12.1 Measure insulin doses accurately. 12.2 Measure heparin dosage and flow rates, verifying that they fall within the normal daily range.

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Math and Dosage Calculations for Health Care Third Edition Booth & Whaley

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  1. Math and Dosage Calculations for Health CareThird EditionBooth & Whaley Chapter 12: Specialized Calculations

  2. Learning Outcomes 12.1 Measure insulin doses accurately. 12.2 Measure heparin dosage and flow rates, verifying that they fall within the normal daily range. 12.3 Calculate the hourly flow rate for IV infusions ordered in milligrams per minute.

  3. Learning Outcomes (cont.) 12.4 Calculate IV flow rates for medications ordered in mg/kg doses. 12.5 Calculate IV flow rates for titrated medications. 12.6 Determine the percentages of solutions, dilutions, and solids. 12.7 Prepare solutions from a concentrate.

  4. Introduction • Specialized calculations include • Insulin • Heparin • Critical care IV fluids • Preparation of solutions • Alligations • These special calculations require extra effort

  5. Pancreas Insulin • High Alert Medication • Pancreatic hormone that stimulates glucose metabolism • With low or no insulin production • Insulin-dependent diabetes • Routine injections of insulin needed to keep glucose (blood sugar) from rising • Generally administered Sub-Q (rotate sites)

  6. Insulin – TYPES • Beef and pork – derived from the pancreas • Human insulin • Replaced beef and pork in the U.S. • Produced using genetically engineered bacteria • Insulin Lispro • Synthetic form

  7. Insulin – TIMING OF ACTION • Rapid-acting • Administer 30 to 60 minutes before meals • Regular (R) and Semi-lente (S) • Very rapid acting • Administer 15 minutes before meal • Insulin Lispro

  8. Insulin – TIMING OF ACTION (cont.) • Intermediate-acting • Lente (L), NPH (N), and Protamine Zinc (P) • Long-acting • Ultralente (U) • Lantus • Newer type • Maintains constant blood levels

  9. Insulin – TIMING OF ACTION (cont.) • Onset • Time when insulin begins to lower blood glucose • Peak • Time when insulin’s effect is the greatest • Duration • Length of time the effect of insulin lasts • Measured from the time of onset

  10. Insulin – TIMING OF ACTION (cont.) Example Regular insulin injection administered at 0700 • Onset – 30 minutes, 0730 • Peak – 2.5 to 5 hours post administration, between 0930 and 1200 • Duration – 8 h, until 1530

  11. Insulin – TIMING OF ACTION (cont.)

  12. Insulin – LABELS Manufacturer Expiration date and lot # Concentration Brand name Type Storage information Species

  13. Concentration Usually listed twice as 100 units/mL – traditional form U-100 (100 units/mL) insulin Source Beef Pork Human Insulin – LABELS (cont.)

  14. Insulin Syringes • Marked in units • Measures amount of insulin (units) not volume of solution • 100 unit capacity • 50 unit capacity • 30 unit capacity • Calibrated in 1 or 2 unit increments

  15. Insulin Syringes (cont.) Rule 12-1 For more accurate measurements use a 50 unit capacity insulin syringe for insulin doses less than 50 units, and a 30 unit capacity insulin syringe for doses less than 30 units.

  16. Insulin Syringes (cont.) Example Ordered: Humulin N 66 units Use a 100 unit capacity syringe Ordered: Humulin R 8 units Use a 30 unit capacity syringe

  17. Insulin Syringes (cont.) Rule 12-2 When using U-500 or a dose of insulin over 100 units use a tuberculin or standard syringe. Calculate the amount to administer in milliliters.

  18. Insulin Syringes (cont.) Example Determine amount of insulin to give. Ordered: Humulin R U-500 insulin, 120 units Amount to administer = 0.24 mL Use a tuberculin syringe

  19. Patient Education: MEASURING A SINGLE INSULIN DOSE 1. Always wash your hands before handling insulin and syringes. 2. If you are using an intermediate- or long-acting insulin (Lente, NPH, Ultralente, 70/30, or 50/50), roll the vial between your palms to mix the insulin until all of the insulin looks cloudy.

  20. Patient Education: MEASURING A SINGLE INSULIN DOSE (cont.) 3. Cleanse the rubber stopper of the vial with an alcohol wipe, using a circular motion. Start at the center of the circleand work outward.

  21. 12-21 Patient Education: MEASURING A SINGLE INSULIN DOSE (cont.) 4. Draw up an amount of air equal to your insulin dose in the syringe. Pull back the plunger until the leading ring is aligned with the correct marking on the syringe.

  22. Patient Education: MEASURING A SINGLE INSULIN DOSE (cont.) 5. Inject the air into the insulin vial. 6. Keep the needle inserted through the stopper and turn the vial upside down. Draw up your ordered dose of insulin.

  23. Patient Education: MEASURING A SINGLE INSULIN DOSE (cont.) 7. Avoid touching the needle during the procedure. 23

  24. Insulin Combinations • Provide greater control over glucose levels • Two types of insulin • Intermediate-acting • Short-acting

  25. Insulin Combinations (cont.) • Manufacturer combines some types • Novolin 70/30 • 70% NPH insulin • 30% regular insulin • Humulin 50/50 • 50% NPH insulin • 50% regular insulin

  26. Insulin Combinations (cont.) • Insulin pens • Self-administration without having todraw up medicationfrom separatebottles 12-26

  27. Insulin Combinations (cont.) Rule 12-3 When preparing a combined insulin dose, always draw up the rapid-acting insulin first. Remember: the insulin with a quicker onset is drawn up first. Clear then Cloudy Clear Cloudy

  28. Insulin Combinations (cont.) Example Ordered: Novolin R 20 units and Humulin N 15 units Sub-Q now Draw up the rapid-acing (clear) insulin first 20 units of Novolin R Then draw up the intermediate-acting (cloudy) insulin 15 units of Humulin N

  29. Insulin Combinations (cont.) Rule 12-4 To prepare a combined insulin dose: 1. Calculate the total dose of insulin: dose of rapid-acting insulin + dose of intermediate-acting insulin total dose insulin

  30. Insulin Combinations (cont.) Rule 12-4 (cont.) 2. Draw up an amount of air equal to the dose of intermediate-acting insulin. • Inject it into the intermediate insulin vial, but do not draw up the dose. • Withdraw the needle from this vial. 3. Draw up an amount of air equal to the dose of rapid-acting insulin. • Inject it into the rapid-acting insulin vial.

  31. Insulin Combinations (cont.) Rule 12-4 (cont.) 4. Without withdrawing the needle from the stopper, invert the vial. Draw up the dose of rapid-acting insulin. 5. Carefully insert the needle through the stopper of the intermediate-acting insulin vial. • Invert the vial, without injecting any of the rapid-acting insulin into the vial.

  32. Insulin Combinations (cont.) Rule 12-4 (cont.) 6. Draw up intermediate-acting insulin until the leading ring reaches the calibration indicating the total dose. • If you accidentally draw up more than the total amount desired, do not push the excess back into the vial. • You must begin the procedure again.

  33. Insulin Combinations (cont.) Example Ordered: Humulin N 42 units and Humulin R 10 units Sub-Q daily How many units will be in the syringe after both insulins have been drawn up into the syringe? 52 units of insulin

  34. Error Alert! When two types of insulin are combined, measure the correct amount of each.

  35. Practice True/False Onset is the time when insulin begins to lower the glucose level. Duration is measured from the time the insulin dose was administered. When mixing insulins, draw up the cloudy before the clear. Insulin is administered using special syringes marked in units. T F From the time of onset F Clear then cloudy T

  36. Heparin • High Alert Medication • Anticoagulant • Reduce or prevent blood clotting • Administered IV or Sub-Q (rotate sites) • Flush solution for heparin locks

  37. Heparin (cont.) • Measured in USP units • Dosage calculations must be accurate • Safe adult dosage range • 20,000 to 40,000 units/24h • Verify that calculated doses fall within this range • Infuse using an infusion pump to ensure accuracy

  38. Heparin – CALCULATIONS • Desired dose represents a flow rate • Quantity of units per period of time • Infuse using an infusion pump to ensure accuracy. • Drop rate used to verify pump rate or if the tubing is removed from the pump temporarily.

  39. Heparin – CALCULATIONS (cont.) Rule 12-5To determine the rate to administer a solution containing heparin with an electronic device that measures the infusion in mL per hour find A, where D = rate of the desired dose Q = dosage unit H = dose on hand A = amount to administer Calculate using your chosen calculation method.

  40. Heparin – CALCULATIONS(cont.) Example Use your chosen calculation method to find hourly rate to administer IV heparin. Ordered: 1000 units/h IV heparin using an infusion pump On hand: 50,000 units heparin in 1000 mL D5W H = 50,000 units; Q = 1000 mL; D = 1000 units/h A = 20 mL/h

  41. Heparin – CALCULATIONS (cont.) Rule 12-6To calculate the hourly dose (D), multiply the total dosage by the hourly flow rate. Determine the following: H = dose on hand or total amount to administer Q = dosage units for the total amount A = amount to administer or the flow rate of the infusion Calculate using your chosen calculation method.

  42. Heparin – CALCULATIONS (cont.) Example What is the hourly dose? Ordered: 30,000 units of IV heparin in 500 mL to D5W to infuse at 25 mL/h H = 30,000 units; Q = 500 mL; A = 25 mL/h D = 1500 units/h

  43. Heparin – CALCULATIONS (cont.) Example Next determine if 1500 units/h is a safe dose. 36,000 units/day is within the safe range of 20,000 to 40,000 units/day

  44. Practice What is the hourly dosage for an infusion of 45,000 units heparin in 1200 mL of D5W infusing at 30 mL/h? Is this a safe dose? Answer 1125 units/h Is this a safe dose? This is a safe dose.

  45. Critical Care IV • IV medications used in critical care settings • Fast-acting and potent • Narrow margin of safety • Administered continuous, IV push, or bolus • Used to alter or maintain • Heart rate • Cardiac output • Blood pressure • Respirations

  46. Critical Care IV – PER MINUTE ORDERS Rule 12-7 To convert a per minute order to an hourly rate: 1. Convert the order to mL/min. Determine the following: D = rate of desired dose (mg or mcg/min) Q = dosage unit (mL) H = dose on hand (mg or mcg/min) A = amount to administer (mL/min) Calculate using your chosen calculation method.

  47. Critical Care IV – PER MINUTE ORDERS (cont.) Rule 12-7 (cont.) 2. Convert mL/min to mL/h • Either by multiplying by 60 or if using dimensional analysis use the factor 60/1 as part of your equation • Both ways the hourly flow rate will be determined in mL/h

  48. Critical Care IV – PER MINUTE ORDERS (cont.) Example Find the hourly flow rate. Ordered: 5000 mg Esmolol in 500 mL D5W at 8 mg/min via infusion pump H = 5000 mg; Q = 500 mL; D = 8 mg/min A = 0.8 mL/min × 60 = 48 mL/h

  49. Critical Care IV – ORDERS BASED ON BODY WEIGHT Rule 12-8To find the IV flow rate based upon weight: • Convert the weight to kg • Determine the desired dose • Calculate the amount to administer • Calculate the flow rate

  50. Critical Care IV – ORDERS BASED ON BODY WEIGHT (cont.) Example Find the flow rate for an adult weighing 187 lb. Ordered: Acyclovir 5 mg/kg IV in 100 mL D5W over 1 hour, q 8 hours X 7 days On hand : Acyclovir 1000 mg/20 mL. Label instructions are to dilute to a dosage strength of 7 mg/mL or less. Convert wt to kg: 178 lb = 85 kg Determine desired dose: D = 425 mg

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