Transcript Pound-kilogram conversion spreadsheet

SSAC2007.WY159.JZ1.1
Computing Dosage for Infants and
Children
Calculation of Dosage Using the Body Weight Method
Calculate pediatric dosage using the
child’s weight in kilograms and the
manufacturer’s recommended daily
dose based on the weight in
kilograms.
Core Quantitative Issue
Ratio and proportion
Supporting Quantitative Skill
Unit conversions
Prepared for SSAC by
*JIAN ZOU – SOUTH SEATTLE COMMUNITY COLLEGE*
© The Washington Center for Improving the Quality of Undergraduate Education. All rights reserved. *YEAR*
1
Math and Meds
Calculating dosage is a fundamental skill for nurses. The
calculations hinge on understanding ratios and proportions.
The textbook/workbook Math and Meds for Nurses by Dolores F.
Saxton, Norma Ercolano and Colleen Glavinsplehs (Delmar
Learning, 2005; first edition by Saxton and Ercolano, 1998)
covers the subject in great detail and with many examples. We
will work through a variation on one of those examples in this
module to demonstrate how such calculations are facilitated by
using a spreadsheet.
Problem:
Ryan’s pediatrician has prescribed 25 mg/kg/day amoxicillin oral
suspension in three divided doses. From the drug book, you find
that the manufacturer recommends 20 – 40 mg/kg/day in three
divided doses every 8 hours. Your pharmacy supplies bottles of oral
suspension labeled 125 mg per 5 mL. Ryan weighs 40 lb. How many
mL should you administer every 8 hours?
-- adapted from Saxton and Ercolano, 1998,
p. 211, problem 2.
2
Overview of Module
According to Math and Meds (1998, p. 207), “Even minor mistakes in
administering medication to an infant or child can be extremely
serious because of differences in their ability to absorb, distribute,
metabolize, and excrete substances such as drugs.” This module is
designed to show you how to calculate the amount of medication to be
administered to an infant or a child according to the physician’s
prescription, the manufacturer’s recommended daily dose per
kilograms of body weight, and the body weight of the child.
Slides 4-6 Build the pound-to-kilogram conversion spreadsheets.
Slide
7 Gives the formulas to use to calculate the dosage in mg.
Slides 8-9 Build the spreadsheets to calculate the dosages.
Slide 10
Calculates the dosage in mL.
Slides11-12 Build the spreadsheet to calculate the dosages in ml
Slides 13 End of module assignment
3
Solving dosage question: Pound-kilogram conversion
Infants and children should take only the amount of medication that is
considered safe for their body weight. This immediately introduces a
problem: whereas the patient’s body weight is generally measured in
pounds, most drug books and drug manufacturers give recommended
pediatric dosages in terms of body weight in kilograms, and many
physicians also prescribe medications using these units. The first goal,
then, is to become proficient in converting between pounds and kilograms.
You often hear that one kilogram is the same as 2.2 pounds. So to
convert a child’s weight from pounds to kilograms, you divide the
number of pounds by 2.2.
Example:
a child weighs 44 lb,
44 ÷ 2.2 = 20 kilograms,
so the child weighs 20 kilograms.
We can be more accurate and say that one kilogram is the
same as 2.2046 pounds. So to convert pounds to kilograms,
divide the number of pounds by 2.2046. With Excel, dividing
by 2.2046 is as easy as dividing by 2.2.
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Solving dosage question: Pound-kilogram conversion spreadsheet
B
C
2 pounds
kilograms
3
5
2.27
4
6
2.72
5
7
3.18
6
8
3.63
7
9
4.08
8
10
4.54
9
11
4.99
10
12
5.44
11
13
5.90
12
14
6.35
13
15
6.80
14
16
7.26
15
17
7.71
16
18
8.16
17
19
8.62
18
20
9.07
Instead of converting pounds to kilograms one by one, we are
going to build a conversion table by Excel.
In a new Excel worksheet,
• type pounds in Cell B2 and kilograms in Cell C2;
• enter numbers 5 through 20 in the pounds column;
• type the Excel formula that divides the value in B3 by 2.2046
hence converting the number of pounds in Cell B3 to number of
kilograms;
• copy Cell C3 and paste it through C4 to C18, converting pounds
in all the cells to kilograms. We obtain a table like the one on the
left.
Task #1:
Create a similar Excel conversion table that converts
pounds to kilograms for 12 – 40 pounds.
= cell with a number in it
All formulas in Excel start with a = sign.
= cell with a formula in it
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Solving dosage question: Pound-kilogram conversion spreadsheet (2)
B
2 pounds
3
4
5
6
7
8
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10
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12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
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17
18
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20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
C
kilograms
5.44
5.90
6.35
6.80
7.26
7.71
8.16
8.62
9.07
9.53
9.98
10.43
10.89
11.34
11.79
12.25
12.70
13.15
13.61
14.06
14.52
14.97
15.42
15.88
16.33
16.78
17.24
17.69
18.14
D
Your completed Task #1 should
look like this
= cell with a number in it
= cell with a formula in it
You can enter numbers 12 through 40
in the pounds column without typing
them one by one: enter 12, 13, and 14
in Cells B3, B5, and B5; highlight
these three cells; place your cursor at
the lower right corner of the
highlighted block and drag the corner
down.
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Solving dosage question: Ratio and proportion: Patient’s dosage per day
From the lb-kg conversion spreadsheet, Ryan’s body weight 40 lb = 18.14 kg.
The ratio of prescribed 25 mg per day to 1 kg must equal the ratio of Ryan’s
dosage in mg per day to his body weight 18.14 kg. Write Ryan’s dosage per day
as x mg, set up the proportion, and then –
25 mg
x mg

1 kg 18.14 kg
or x 
25
*18.14  453.6 mg
1
So, Ryan should take 453.6 mg per day in three divided doses, that is
453.6/3=151.2 mg every 8 hours.
In general, we have
patient' s dosage per day
prescribed dosage per day

patient' s body weigh t in kg
1 kg
or
(patient’s dosage per day)
= (prescribed dosage per kg per day) x (patient’s body weight in kg)
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Solving dosage question: Patient’s dosage per day: Spreadsheet
2
3
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5
6
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B
C
Patient's weight
in lb
in kg
D
Prescribed
mg/kg/day
E
Patient's dosage
mg/day
We are going to build a spreadsheet to
calculate the dosages for patients of
body weights from 12 lb through 42 lb
with the prescribed dosage of 25
mg/kg/day.
In the first row of a new Excel
spreadsheet:
• Type Patient’s weight, Prescribed,
and Patient’s dosage in Cells B2, D2,
and E2, respectively;
= cell with a number in it
• Type in lb, in kg, mg/kg/day, and
mg/day in Cells B3, C3, D3, and E3,
respectively.
= cell with a formula in it
The spreadsheet should look like the
one on the left.
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Solving dosage question: Patient’s dosage per day: Spreadsheet (2)
B
C
D
2 Patient's weight
Prescribed
3
in lb
in kg
mg/kg/day
4
12
5.44
5
13
5.90
6
14
6.35
7
15
6.80
8
16
7.26
9
17
7.71
10
18
8.16
11
19
8.62
12
20
9.07
13
21
9.53
14
22
9.98
15
23
10.43
16
24
10.89
17
25
11.34
18
26
11.79
19
27
12.25
20
28
12.70
21
29
13.15
22
30
13.61
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31
14.06
24
32
14.52
25
33
14.97
26
34
15.42
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35
15.88
28
36
16.33
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16.78
30
38
17.24
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39
17.69
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40
18.14
33
41
18.60
34
42
19.05
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
= cell with a number in it
= cell with a formula in it
E
Dose/day
mg/day
136.1
147.4
158.8
170.1
181.4
192.8
204.1
215.5
226.8
238.1
249.5
260.8
272.2
283.5
294.8
306.2
317.5
328.9
340.2
351.5
362.9
374.2
385.6
396.9
408.2
419.6
430.9
442.3
453.6
464.9
476.3
• Enter pound number from 12 through 42 in Cells
B4 through B34.
• In Cell C4, enter the formula that converts pounds
in B4 to kilograms.
• Copy C4 and paste it to Cells C5 though C34,
converting pounds in Cells B5 through B34 into
kilograms.
• Enter the prescribed dose per kg body weight
per day (25) in Cells D4 through D34.
• In E4, enter the formula that multiplies the body
weight in kg in Cell C4 by the dose per kg per day
in Cell D4, to obtain the dose per day for the
patient, and paste it to cells through Cell E5
through E34.
The completed spreadsheet should look like the
one on the left.
Ryan weighs 40 lb. So from
the table, his daily dose
should be 453.6 mg
9
Solving dosage question: Ratio and proportion: Med per administration
Now we find out the amount of oral suspension
Ryan should take each time.
Divide the daily dose by 3 to get 453.6÷3=151.2 mg. So Ryan should take 151.2
mg of amoxicillin each time.
The available oral suspension contains 125 mg of amoxicillin per 5 mL. To find the
amount of oral suspension in mL, x mL, that contains 151.2 mg of amoxicillin, we
set up the proportion:
125 mg 151.2 mg

5 mL
x mL
Solving the above proportion, we get
125 mg
x  151.2 mg  (
)  6 mL
5 mL
The amount of oral suspension for every 8 hours
= (dose per each time) / (the mg to mL ratio of the oral suspension)
Ryan should take 6 mL of the oral suspension each time for three times a day.
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Solving dosage question: Med per administration: Spreadsheet
We are going to use the spreadsheet to calculate the amount of oral suspension to be taken
each time for children of various weights.
Type mg/8hours in cell F3, mg/mL in Cell
G3, and mL/8hour in Cell H3
• Enter the formula that divides the dose per
day by 3 to obtain the dose per 8 hours in Cell
F4, then paste it in Cells F5 through F34
• Enter the ratio of the mg to mL of the
available oral suspension in Cell G4 and
paste it in Cells G5 through G34;
• Enter the formula that calculates the
amount of oral suspension in Cell H4 and
paste it in Cells H5 through H34.
The completed spreadsheet is on the next
slide.
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Solving dosage question: Med per administration: Spreadsheet (2)
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B
C
D
Patient's weight
Prescribed
in lb
in kg
mg/kg/day
12
5.44
13
5.90
14
6.35
15
6.80
16
7.26
17
7.71
18
8.16
19
8.62
20
9.07
21
9.53
22
9.98
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10.43
24
10.89
25
11.34
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11.79
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12.25
28
12.70
29
13.15
30
13.61
31
14.06
32
14.52
33
14.97
34
15.42
35
15.88
36
16.33
37
16.78
38
17.24
39
17.69
40
18.14
41
18.60
42
19.05
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
E
F
G
H
Dose/day
Suspension
mg/day
mg/8hours mg/mL
mL/8hours
136.1
45.4
25.0
1.8
147.4
49.1
25.0
2.0
158.8
52.9
25.0
2.1
170.1
56.7
25.0
2.3
181.4
60.5
25.0
2.4
192.8
64.3
25.0
2.6
204.1
68.0
25.0
2.7
215.5
71.8
25.0
2.9
226.8
75.6
25.0
3.0
238.1
79.4
25.0
3.2
249.5
83.2
25.0
3.3
260.8
86.9
25.0
3.5
272.2
90.7
25.0
3.6
283.5
94.5
25.0
3.8
294.8
98.3
25.0
3.9
306.2
102.1
25.0
4.1
317.5
105.8
25.0
4.2
328.9
109.6
25.0
4.4
340.2
113.4
25.0
4.5
351.5
117.2
25.0
4.7
362.9
121.0
25.0
4.8
374.2
124.7
25.0
5.0
385.6
128.5
25.0
5.1
396.9
132.3
25.0
5.3
408.2
136.1
25.0
5.4
419.6
139.9
25.0
5.6
430.9
143.6
25.0
5.7
442.3
147.4
25.0
5.9
453.6
151.2
25.0
6.0
464.9
155.0
25.0
6.2
476.3
158.8
25.0
6.4
From the table, with the body
weight of 40 lb, Ryan should
take 6 mL each time.
= cell with a number in it
= cell with a formula in it
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End of Module Assignment
1.
One inch equals 2.54 cm. A child is 54 in tall. What is the
child’s height in cm?
2.
Build a spreadsheet that converts 12 through 60 inches to
centimeters.
3.
A physician has prescribed for a baby of 20 lb a medication
15 mg/kg/day to be administered in divided doses every 12
hours. The drug on hand is labeled 75mg per 2 mL.
(a) Calculate how many mL of the drug the nurse should
administer each time?
(b) Build a spreadsheet to calculate the doses to be
administered each time for babies with weights varying from
15 lb to 25 lb.
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Pre and post module test
1.
Write the ratio of 30 students to 40 chairs.
2.
A vial of Kantrex Injection is labeled 75 mg per 5 mL. Write the
ratio of mL to mg.
3.
You drove your car 500 miles and used 20 gallons of gas. At the
same ratio, how many miles would you expect to drive on 15
gallons of gas?
4.
A nurse finds that the manufacturer’s recommended dosage for
a certain drug is 12 mg per kg of body weight per day. At this
ratio, what is the daily dosage for a child of 39 lb?
5.
One tbsp = 15.0 mL. How many tablespoonfuls (tbsp) are there
in 75 mL?
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