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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

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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 11: Calculations for Special Populations McGraw-Hill

  2. Learning Outcomes 11.1 Explain why dosages for special populations must be based on the individual patient. 11.2 Identify factors that affect the absorption, distribution, biotransformation, and elimination of drugs in special populations. McGraw-Hill

  3. Learning Outcomes (cont.) 11.3 Determine safe doses for special populations. 11.4 Calculate patient dosages based on body weight. 11.5 Find a patient’s body surface area (BSA). McGraw-Hill

  4. Learning Outcomes (cont.) 11.6 Calculate patient dosages based on a patient’s BSA. 11.7 Describe volume and medication limitations for special populations. 11.8 Calculate infusion rates based upon body weight. McGraw-Hill

  5. Introduction • Two populations requiring extra consideration when calculating medication dosages • Pediatric (less than 18 years old) • Geriatric (over 65 years old) • Risk of harm is far greater due to the way they break down and absorb medications. McGraw-Hill

  6. Introduction (cont.) • Clarify all confusing drug orders • Calculate with absolute accuracy • Verify that dose is safe • Seek assistance from your supervisor Do not take short cuts with medication calculations. McGraw-Hill

  7. Factors That Impact Dosing • Standardized doses based on assumptions • The patient’s body and age • Body systems are fully developed and functioning • Assumptions do not hold true for all populations or situations McGraw-Hill

  8. Factors That Impact Dosing –PHARMACOKINETICS • Study of how drugs are used by the body • Absorption • Distribution • Biotransformation • Elimination • Understanding these processes allows for adjustments for special populations McGraw-Hill

  9. Factors That Impact Dosing –PHARMACOKINETICS (cont.) • Absorption • Process that moves a drug from the site where it is given into the bloodstream • IV medications bypass the absorption process • Oral medications – digestive system • Topical – through the skin McGraw-Hill

  10. Factors That Impact Dosing –PHARMACOKINETICS (cont.) • Distribution • Process that moves the drug from the bloodstream to other body compartments • Target site – where the drug produces its desired effect McGraw-Hill

  11. Factors That Impact Dosing –PHARMACOKINETICS (cont.) • Biotransformation • Process that chemically changes the drug in the body • Occurs primarily in the liver • Helps to protect the body from foreign chemicals including drugs McGraw-Hill

  12. Factors That Impact Dosing –PHARMACOKINETICS (cont.) • Elimination • Process where the drug leaves the body • Main route – urine • Other ways • Air that we exhale • Sweat • Feces • Breast milk • Other body secretions McGraw-Hill

  13. Factors That Impact Dosing –PHARMACOKINETICS (cont.) • Adjust dose • If one of the four processes are not functioning within certain limits • Made according to nature and severity of patient’s condition • May by higher or lower than standard doses McGraw-Hill

  14. Factors That Impact Dosing (cont.) • Conditions that impact dosing • Stomach or intestinal disorders • Liver disorders • Obesity • Kidney disease • Functions of body systems change over the life of a person. McGraw-Hill

  15. Factors That Impact Dosing (cont.) • Newborns – systems not fully developed • pH of stomach is lower • Thinner skin • Liver still developing • Less circulation to muscles • Geriatrics – systems deteriorate • Skin and veins become fragile • Decreased liver function • Decreased kidney function • Poor circulation McGraw-Hill

  16. Working with Special Populations • Other Considerations • Parent or caretaker may be administering or assisting with medications. • Educate regarding medications • Geriatric patients may have decreased awareness or understanding. McGraw-Hill

  17. Working with Special Populations – GERIATRIC PATIENTS • Show respect • Listen to their concerns • Encourage them to • Use the same pharmacy to fill all prescriptions • Have one primary care physician to monitor and approve all medications • Keep a list of all medications McGraw-Hill

  18. Special Populations –GERIATRIC PATIENTS (cont.) • Decreased dexterity • Injections • Eye drops • Open bottles • Difficulty swallowing • Drugs that cannot be crushed • Foods that can be mixed with drugs McGraw-Hill

  19. Hearing loss Do they understand instructions? Have them repeat information back to you Difficulty reading small print Labeling Tablet colors Special Populations –GERIATRIC PATIENTS (cont.) McGraw-Hill

  20. Special Populations –GERIATRIC PATIENTS (cont.) • Short-term memory loss • Written instructions • Medication calendars • Pill dispensers • Avoid OTC or herbal meds until discussing with physician. • Do not take expired meds or borrowed meds. McGraw-Hill

  21. Teaching Patients About Medications 1. Name of the medication 2. Purpose 3. How to store it 4. How long to take the medication 5. How and when to take it 6. How to know if it is effective McGraw-Hill

  22. Teaching Patients About Medications(cont.) 7. Required follow-up tests, doctor appointments 8. Possible side effects and what to do 9. Interactions with other drugs and foods 10. Symptoms to report to the doctor 11. What to do if a dose is missed 12. Keeping a list of all medications McGraw-Hill

  23. Dosages Based on Body Weight • Amount of medication per • Weight of the patient per • Unit of time mg/kg/h McGraw-Hill

  24. Dosages Based on Body Weight Rule 11-1Calculating dosage based on body weight: 1. Convert the patient’s weight to kilograms 2. Calculate the desired dose D by multiplying dose ordered by the weight in kilograms such as McGraw-Hill

  25. Dosages Based on Body Weight(cont.) Rule 11-1(cont.) 3. Confirm whether or not the desired dose is safe by checking the label, package insert, or product literature. 4. Calculate the amount to administer, using fraction proportion, ratio proportion, dimensional analysis, or the formula method. McGraw-Hill

  26. Dosages Based on Body Weight(cont.) Calculate the amount to administer to a 3-year-old weighing 34 lb. Ordered: hysocyamine sulfate 5 mcg/kg subq 1 h pre-anesthesia On hand: hysocyamine sulfate 0.5 mg/mL Convert 34 lb to kg = 15.5 kg Example McGraw-Hill

  27. Dosages Based on Body Weight(cont.) Find the desired dose: 77.5 mcg = D Find the amount to administer: 77.5 mcg = 0.0775 = 0.08 mg Amount to administer = 0.16 mL Example (cont.) McGraw-Hill

  28. Dosages Based on Body Weight(cont.) • Pediatric injection volume • Limited to size and age of the child • Length and gauge of needle vary with age and size of the patient • Geriatric injections • Depth of injection may also vary due to reduce muscle size McGraw-Hill

  29. Pediatric Injections McGraw-Hill

  30. Ensuring Safe Dosages • Drug orders – written in several ways • Check to see if dose ordered is a standard recommended dose • Not less than the minimum or • Not greater than the maximum McGraw-Hill

  31. Ensuring Safe Dosages (cont.) Rule 11-2Ensuring Safe Dosages When working with special populations, always check the package insert, drug label, or product literature to ensure the safety of the dose to be administered. McGraw-Hill

  32. Error Alert ! Convert ounces carefully. • The weight of babies may be measured in pounds and ounces or grams. • 16 oz = 1 lb, an ounce is not a tenth of a pound. • A baby who weighs 8 lb 6 oz does not weigh 8.6 lb. McGraw-Hill

  33. Error Alert ! Weight 8 lb 6 oz Convert 6 ounces to pounds using as the conversion Therefore 8 lb 6 oz = 8.375 lb McGraw-Hill

  34. Practice Determine whether the following order is safe. If safe, calculate the amount to administer. Patient: Child who weighs 14.5 kg Ordered: Amoxil 75 mg PO q8h On hand: Usual child dose 20-40 mg/kg day q8h Answer Dosage doesn’t fall within recommended dosage range; contact the physician. McGraw-Hill

  35. Dosages Based on Body Surface Area (BSA) • BSA calculations Provide more accurate dosage calculations that are specific to the patient’s size and severity of his/her illness. McGraw-Hill

  36. Dosages Based on BSA – CALCULATING BSA • BSA is stated in square meters (m2) • Must know height and weight • Use a formula or a special chart called a nomogram McGraw-Hill

  37. Dosages Based on BSA – CALCULATING BSA (cont.) Rule 11-3 Calculating the BSA using a formula: 1. If you know the height in cm and weight in kg, calculate McGraw-Hill

  38. Dosages Based on BSA – CALCULATING BSA (cont.) Rule 11-3 (cont.) 2. If you know the height in inches and weight in pounds, calculate If the result is less then one, round to nearest hundredth. If the result is greater than one, round to nearest tenth. McGraw-Hill

  39. Dosages Based on BSA – CALCULATING BSA (cont.) Find the body surface area for an adult who is 5’6” tall and who weighs 168 lb. BSA = 1.88 m2 Example McGraw-Hill

  40. Dosages Based on BSA – CALCULATING BSA (cont.) Rule 11-4 Calculating BSA using a Nomogram: Using a straight edge, align the straight edge so it intersects at the height and weight. Doing so will create an intersection in the BSA scale. McGraw-Hill

  41. Dosages Based on BSA – CALCULATING BSA (cont.) Find the body surface for a baby who is 24 in and weighs 14 lb and 8 oz. Use the “Child’s Nomogram” BSA = 0.21 m2 Example McGraw-Hill

  42. Calculating Dosage Based on BSA Rule 11-5 Calculating dosage based on BSA: 1. Calculate the patient’s BSA. 2. Calculate the desired dose: dosage ordered per m2 x BSA = desired dose 3. Confirm whether the desired dose is safe. 4. Calculate the amount to administer, using fraction proportion, ratio proportion, or the formula method. McGraw-Hill

  43. Calculating Dosage Based on BSA (cont.) Ordered: CeeNU (1st dose) 140 mg now for a child 38 in tall and weighing 47 lb According to the package the first dose is a single oral dose providing 130 mg/m2 . BSA = 0.76 m2 Desired dose should be 98.8 mg (based on recommended dosing) Ordered dose of 140 mg is too large for the patient. Example McGraw-Hill

  44. Practice Patient: 34 cm tall, 5 kg Ordered: Cerubidine 5.5 mgIV weekly On hand: Cerubidine injection 5mg/mL when reconstituted Recommended pediatric dose 25 mg/m2 If dose is safe, calculate amount to administer: BSA = 0.22 m2 Desired dose = 5.5 mg Dose ordered is a safe dose Amount to administer = 1.1 mL McGraw-Hill

  45. Daily Maintenance Fluid Needs (DMFN) • Children’s bodies contain a higher percentage of water than adults’ bodies • Children and critically ill patients are at risk for: • Fluid overload • Dehydration • Electrolyte imbalance McGraw-Hill

  46. Daily Maintenance Fluid Needs (DMFN)(cont.) • Monitor both the amount of medication and the amount of fluid a patient receives • Fluids can be calculated on: • Body weight • Body surface (BSA) • Metabolism • Age McGraw-Hill

  47. Daily Maintenance Fluid Needs (DMFN)(cont.) • Represents the fluid needed over 24 hours • Combines: • Maintenance fluids, orally and parenterally • Medication • Diluent for medication • Fluids used to flush the injection port McGraw-Hill

  48. Daily Maintenance Fluid Needs (DMFN)(cont.) • Amount of maintenance fluid required varies by weight • Replacement fluids • Based on patient’s condition • Vomiting • Diarrhea • Fever McGraw-Hill

  49. Daily Maintenance Fluid Needs (DMFN) (cont.) Rule 11-6 To calculate daily maintenance fluid needs (DMFN) based on weight: 1. If the patient weighs up to 10 kg, find 2. If the patient weighs 10 to 20 kg, find McGraw-Hill

  50. Daily Maintenance Fluid Needs (DMFN) (cont.) Rule 11-6(cont.) 3. If the patient weighs over 20 kg, find McGraw-Hill