Transcript Chapter 12 Calculations for Special Populations - McGraw

PowerPoint® to accompany
Math and Dosage Calculations for
Medical Careers
Second Edition
Booth • Whaley
Chapter 11
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Chapter 11 Calculations for
Special Populations
Learning Objectives
When you have completed Chapter 11,
you will be able to:



Explain why dosages for specific populations
must be based on the individual patient.
Identify factors that affect the absorption,
distribution, biotransformation, and
elimination of drugs in special populations.
Determine safe doses for special population
patients.
Chapter 11
3
Learning Objectives



(con’t)
Calculate patient dosages based on
body weight.
Find a patient’s body surface area
(BSA).
Calculate patient dosages based on a
patient’s BSA.
Chapter 11
4
Learning Objectives


(con’t)
Describe volume and medication
limitations for special populations.
Calculate infusion rates based upon
body weight.
Chapter 11
5
Introduction

Two special populations require extra
consideration when calculating
medication dosages.



Pediatric (children under age 18)
Geriatric (mature adults over age 65)
Risk of harm is far greater due to way
they break down and absorb
medications.
Chapter 11
6
Introduction




(con’t)
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
Chapter 11
7
Factors that Impact Dosing

Normal dose of medication makes
assumptions



About the patient’s body and age
That body systems are fully developed and
functioning
Special populations may need dosages
adjusted due to this assumption not
being true
Chapter 11
8
Pharmacokinetics

Study of how drugs are used by the body




Absorption
Distribution
Biotransformation
Elimination
Understanding these processes allows for
adjustments for special populations
Chapter 11
9
Absorption

Process that moves a drug from the site
where it is given into the bloodstream



IV medications bypass the absorption
process by going directly into the
bloodstream
Oral medications absorbed in digestive
system
Topical absorbed through the skin
Chapter 11
10
Distribution



Process that moves the drug from the
bloodstream to other body tissues and
fluids
Target site is where the drug product
produces its desired effect
Each drug affects drug target sites
Chapter 11
11
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
Chapter 11
12
Elimination



Process where the drug leaves the body
Main way of eliminating is in the urine
Other ways





Air that we exhale
Sweat
Feces
Breast milk
Other body secretions
Chapter 11
13
Drug Adjustment



Adjustment is needed if one of these four
processes are not functioning within certain
limits.
Dose adjustment is made according to nature
and severity of patient’s condition.
You are not expected to make these
adjustments, but be aware that they may
have to be done.
Chapter 11
14
Conditions That Impact
Dosing
Functions of body systems change over
the life of a person
Newborns – systems not developed yet
 Ph of stomach is lower
 Thinner skin
 Liver still developing
 Less circulation to muscles
Chapter 11
15
Conditions That Impact
Dosing (con’t)
Geriatrics – systems begin to deteriorate




Skin and veins become fragile
Decreased liver function
Decreased kidney function
Poor circulation
Chapter 11
16
Working with Special
Populations

Other Considerations
Parent or caretaker may be
administering or assisting them with
medications
 These individuals will need education
regarding any regular or special
requirements

Chapter 11
17
Working with Special
Populations (con’t)


Show respect when working with
geriatric patients
Encourage them


To participate in planning their medication
schedule
To have only one primary physician to
monitor and approve all medications
Chapter 11
18
Working with Special
Populations (con’t)



Geriatric patients may have
decreased dexterity
Ask for bottle caps that are
not childproof
Inform patient when
medication can be crushed
or mixed with applesauce to
aid swallowing
Chapter 11
19
Working with Special
Populations (con’t)



Geriatric patients may
not be able to read
small print
Ask for meds to be
labeled so that they
can easily be read
Do not assume patients
can distinguish
between colors of
tablets
Chapter 11
20
Working with Special
Populations (con’t)




Geriatric patients often have some form of
hearing loss
Have patients repeat instructions and
information
Determine if you need to give written
direction and explanations
Use medication calendars or containers with
days and time meds are to be taken
Chapter 11
21
Teaching Patients
About Medications
1.
2.
3.
4.
5.
6.
Name of the medication
Purpose
How to store it
How long patient needs to take the
medication
How and when to take it
How to know if it is effective
Chapter 11
22
Teaching Patients About
Medications (con’t)
7.
8.
9.
10.
11.
12.
Required follow-up tests, doctor
appointments
Possible side effects and what to
do
Interactions with other drugs and
foods
Symptoms to report to the doctor
What to do if a dose is missed
Keeping a list of all medications
Chapter 11
23
Dosages Based on Body
Weight
Rule 11 - 1
Calculating 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
mg
m cg
x kg  desired dose or
x kg  desired dose
kg
kg
Chapter 11
24
Dosages Based on Body
Weight (con’t)
Rule 11 - 1 (con’t)
3. Confirm whether or not the desired
dose is safe by checking the label,
package insert, or product literature.
If unsafe, consult the physician who
wrote the order
4. Calculate the amount to administer,
using fraction proportion, ratio
proportion, dimensional analysis, or
the formula method
Chapter 11
25
Dosages Based on Body
Weight (con’t)
Example
Calculate the amount to administer to a three-yearold who weighs 34 lb.
Ordered: hysocyamine sulfate 5 mcg/kg subq 1 h
pre-anesthesia
On hand: hysocyamine sulfate 0.5 mg/mL
Answer: 0.15 mL
Chapter 11
26
Injections




Limited to size and age of the child
Length and gauge of needle vary
with age and size of the patient
Smaller muscles need smaller
needles
Depth of injection may also vary
for geriatric patients due to reduce
muscle size
Chapter 11
27
Pediatric Injection (con’t)
Maximum Volume
of IM Injection
0.5-1 mL
Stage of Development
Infant
Toddler,
walking for at
least one year
1 mL
Preschooler and
elementary
school age
1-1.5 mL
Chapter 11
28
Ensuring Safe Dosages



Drug orders may be written in several
ways.
You must check to see if dose is
standard recommended dose.
You need to determine if dose ordered
is not less than minimum or greater
than maximum recommended dose.
Chapter 11
29
Ensuring Safe Dosages
(con’t)
Rule 11 - 2
Ensuring 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.
Chapter 11
30
Error Alert !
Convert ounces carefully.
 The weight of babies is often
measured in pounds and ounces.


Because 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.
Chapter 11
31
Error Alert! (con’t)
Convert 6 ounces to pounds using
1 lb as the conversion
16 oz
6 oz  1lb  0.375 lb
16 oz
Thus, 8 lb 6 oz = 8.375 lb
Chapter 11
32
Ensuring Safe Dosages
(con’t)
Example:
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.
Chapter 11
33
Dosages Based on Body
Surface Area (BSA)



BSA calculations are used to provide
more accurate dosage calculations
specific to the patient’s size and severity
of his/her illness.
Some medications are based on
patient’s body weight only.
Both weight and height are used to
determine a patient’s body surface.
Chapter 11
34
Calculating BSA Using a
Formula



A patient’s BSA is stated in
square meters or m2
To calculate the BSA you must
know the height and weight
Use a formula or a special
chart called a nomogram
Chapter 11
35
Calculating BSA Using a
Formula
Rule 11 - 3:
To determine a patient’s Body Surface Area
(BSA):
1. If you know the height in cm and weight
in kg, calculate
BSA  height (cm)  weight (kg) m2
3600
Chapter 11
36
Calculating BSA Using a
Formula (con’t)
2. If you know the height in
inches and weight in pounds,
calculate
height
(in)

weight
(lb)
BSA 
m2
3131
Chapter 11
37
Calculating BSA Using a
Formula (con’t)
Example:
Find the body surface area for an adult
who is 5’6” tall and who weighs 168 lb.
BSA = 1.9 m2
Chapter 11
38
Calculating the Body Surface Area
(BSA) using a Nomogram
Rule 11 - 4
 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
Chapter 11
39
Calculating the BSA using a
Nomogram (con’t)
Example:
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
Chapter 11
40
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 x BSA = desired dose
3. Confirm whether or not the desired dose is
safe. If unsafe, consult the physician who
wrote the order.
4. Calculate the amount to administer, using
fraction proportions, ratio proportions, or the
formula method. Chapter 11
41
Calculating Dosage Based
on BSA (con’t)
Example:
Ordered: Ceenu (1st dose) 140 mg now
for a child whose height is 38 in and
weight is 47 lb
According to the package the first dose is
a single oral dose providing 130 mg/m2
The dose ordered 140 mg is above the first
recommended dose. Contact the physician.
Chapter 11
42
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
Chapter 11
43
DMFN


(con’t)
You must monitor not only the amount
of medication but the amount of fluid
Fluids can be calculated on:




Body weight
Body surface (BSA)
Metabolism
Age
Chapter 11
44
DMFN


(con’t)
DMFN represent the fluid a patient
needs over 24 hours
Combines:




Maintenance fluids, orally and parenterally
Medication
Diluent for medication
Fluids used to flush the injection port
Chapter 11
45
DMFN

Amount of maintenance fluid required



(con’t)
Depends on weight
For children = 100 mL/kg/day
Replacement fluids


Based on patient’s condition
May be due to



Vomiting
Diarrhea
Fever
Chapter 11
46
DMFN
(con’t)
Rule 11 - 6
To calculate daily maintenance fluid needs
(DMFN) based on weight:
1. If the patient weighs up to 10 kg, find
100 mL  kg  DMFN in mL
1 kg
Chapter 11
47
DMFN
(con’t)
Rule 11 – 6 (con’t)
2. If the patient weighs 10 to 20 kg, find
1000 mL  50 mL  (kg10)  DMFN in mL
1 kg














Chapter 11
48
DMFN
(con’t)
Rule 11 - 6 (con’t)
3. If the patient weighs over 20 kg, find
20
mL
1500 mL 
 (kg  20)  DMFN in mL
1 kg














Chapter 11
49
DMFN
(con’t)
Example:


Find the DMFN for a patient who weighs
16 kg
Answer = 1300 mL
Find the DMFN for a patient who
weighs 24 kg Answer = 1580 mL
Chapter 11
50
IV Fluid Volumes
Rule 11 - 7
For pediatric patients and
critically ill patients, the
amount of solution in the IV
tubing must be considered
when determining infusion
times and volumes.
Chapter 11
51
IV Fluid Volumes



(con’t)
Five feet of standard IV tubing contains
about 10 mL of solution.
With a volume control chamber, a child
will not begin receiving medication until
the 10 mL of solution already in the
tubing has infused.
Low-volume tubing contains only 0.3
mL of solution per 5 feet.
Chapter 11
52
Creatinine Clearance


Liver and kidney functions are often
reduced in geriatric patients
Decreased liver function results in:



Slower metabolism of drugs
Delaying or prolonging the desired
effect of medications
Absorption of drugs may be decreased
Chapter 11
53
Creatinine Clearance



(con’t)
Decreased kidney function
and decreased cardiac
output will slow excretion
of meds
Slower excretion and
reduced metabolism can
cause accumulations of
meds in the body thus
increasing side effects
Can cause toxicity
Chapter 11
54
Creatinine Clearance

Chronic diseases can damage the
kidneys




(con’t)
Hypertension
Diabetes
Congestive heart failure
Drugs can impair kidney function


Lasix
Aminoglycoside antibiotics
Chapter 11
55
Creatinine Clearance



(con’t)
Package inserts discuss safe dosage
levels on creatinine clearance
Creatinine is a by-product found in the
blood as a result of muscle metabolism
Creatine Clearance (ClCR) = indicator of
the rate at which kidneys filter the
blood
Chapter 11
56
Creatinine Clearance



(con’t)
Creatinine clearance
decreases with age.
Creatinine clearance level
is calculated using
information that comes
from analysis of blood
and urine samples.
Physician will factor in a
patient’s creatinine
clearance when writing a
drug order.
Chapter 11
57
Ideal and Actual Body Weight



Geriatric patients have a
decreased proportion of
lean body mass and
water
Certain drugs may bind
to lean tissue or body fat
changing the effect of the
medication
Monitor serum drug
levels
Chapter 11
58
Ideal and Actual Body Weight
(con’t)




Fat-soluble drugs are distributed to
body fat
Elderly have a larger proportion of body
fat
Drugs are therefore distributed to more
tissues
May cause residual effects such as
drowsiness
Chapter 11
59
Ideal and Actual Body Weight
(con’t)


Water soluble drug doses for
overweight patients should be based on
ideal body weight.
If patient is below ideal body weight,
the actual weight should be used.
Chapter 11
60
Determine Safe Dosages
for Geriatric Patients
Rule 11 - 8
Check the package insert or product
literature. Determine the safe dose
based upon renal function and the ideal
or actual body weight of the patient.
If the dose is safe, calculate the amount
to administer.
Chapter 11
61
Determine Safe Dosages for
Geriatric Patients (con’t)
Example:
A 78-year-old male is 5’4” tall and weighs 180
lb. (Ideal weight range is 122–157 lb.) He
has normal renal function and has a nonlifethreatening infection.
Ordered: Garamycin 85 mg IM q 8h
On hand: Garamycin injection, 40 mg/mL (usual
dosage is 1 mg/kg
This is a safe dose - Give 2.1 mL
Chapter 11
62
Error Alert!
For medications that are
strongly bound to lean
body tissue, calculate an
overweight patient’s dose
on ideal body weight, not
actual weight.
Chapter 11
63
Polypharmacy


Polypharmacy refers to the practice of
taking many medications at a time
Many geriatric patients take several
medications



Take prescribed drugs past expiration date
Borrow medications
Look for ways to limit costs and may take
older drugs instead of seeing MD
Chapter 11
64
Drug Interactions
Rule 11 - 9
To identify cases of polypharmacy and
reduce the risk of drug interactions,
ask elderly patients about:
1. All medications they take which are
prescribed by either their primary physician
or specialists
2. Any over-the-counter medications they take
including vitamins, laxatives, and allergy
medications
Chapter 11
65
Drug Interactions
(con’t)
Rule 11 - 9 (con’t)
3. Any social drugs which they use including
alcohol, tobacco, and marijuana
4. Medications that they borrow from family and
friends
5. Herbal and home remedies that they use
including natural supplements such as ginseng,
gingko biloba, and St. John’s wort
Chapter 11
66
Drug Interactions
(con’t)
Each additional medication a
patient takes increases the
likelihood of a drug
interaction.


Can interfere with the
effectiveness of a medication
Can cause serious or even fatal
side effects
Chapter 11
67
Drug Interactions
(con’t)
Factors that cause adverse
drug reactions






Advanced age
Small body size
Multiple illness (including
chronic problems)
Multiple medications
Living alone
Malnutrition
Chapter 11
68
Drugs to be Avoided in
Specific Diseases
Severe Risk
 benign
prostatic
hypertrophy
antihistamines
anti-Parkinson’s
drugs
GI antispasmodics
antidepressants
Chapter 11
69
Drugs to be Avoided in
Specific Diseases (con’t)
Severe Risk

Cardiac
dysrhythmia

Clotting disorders

COPD

GI diseases

Seizures
Tricyclic
antidepressants
Antiplatelet drugs, ASA
Hypnotics, sedatives,
beta blockers
NSAIDs, ASA
Metoclopramide (Reglan)
Chapter 11
70
Drugs to be Avoided in
Specific Diseases (con’t)
Less Severe Risk


Benign prostatic
hypertrophy
Constipation
Narcotics
Antihistamines
anti-Parkinson’s
drugs
GI antispasmodics
antidepressants
Chapter 11
71
Drugs to be Avoided in
Specific Diseases (con’t)
Less Severe Risk
 Diabetes mellitus
 GI diseases
 Insomnia
Steroids, beta
blockers
Aspirin, potassium
supplements
Decongestants,
bronchodilators, some
antidepressants
 Seizures
Antipsychotics
Chapter 11
72
Apply Your Knowledge
True or False
A baby who weighs 6 lb 8 oz
weighs 6.8 lb.
Answer: False
Chapter 11
73
Apply Your Knowledge
True or False
A baby who weighs 9.5 lb
weighs 9 lb 8 oz.
Answer: True
Chapter 11
74
Apply Your Knowledge
Name three resources that you can consult
to see if the calculated dose is a safe
dose to administer.
Answer:
1. Drug label
2. Package insert
3. Drug literature
Chapter 11
75
Apply Your Knowledge
Pediatric dosages should be
rounded to the nearest:
a. Tenth
b. Hundredth
c. Thousandth
Answer: b. Hundredth
Chapter 11
76
Apply Your Knowledge
What two things are pediatric dosages
often based on?
Answer: Weight and BSA
Chapter 11
77
Apply Your Knowledge
The amount of fluid the patient needs
over a 24-hour period is called the
__________?
Answer:
Daily maintenance fluid
needs (DMFN)
Chapter 11
78
Apply Your Knowledge
Which age-related change would
indicate a need to consider a smaller
needle length for an IM injection?
a.
b.
c.
d.
thinner, more fragile skin
loss of subcutaneous tissue
decreased muscle mass
difficulty swallowing
Answer: c. decreased muscle mass
Chapter 11
79
Apply Your Knowledge
The test used to measure the rate at which
the kidneys filter the blood is called:
a. kidney function test creatinine
b. renal function test
c. creatinine
d. creatinine clearance
Answer:
d. creatinine clearance
Chapter 11
80
Apply Your Knowledge

True or False
For medications that are strongly bound
to lean body tissue, calculate an
overweight patient’s dose on the ideal
weight, not actual weight.
Answer: True
Chapter 11
81
Apply Your Knowledge
Polypharmacy occurs when a patient:
a. uses too many pharmacists
b. takes many medications at a time
c. borrows medications from friends
d. sees a variety of health-care providers
Answer:
b. takes many
medications at a time
Chapter 11
82
Calculations for Special
Populations
Perfection
consists not in
doing
extraordinary
things, but in
doing ordinary
things
extraordinarily
well.
-- Angelique
Arnauld
Chapter 11
THE END
83