Transcript Maths – IV Calculations

Topic 3
Math/Drugs Calculations
IV Giving Sets
Generally there are 2 types of giving sets
in use and they deliver drops of different
sizes
 Blood giving sets 15 or 20 drips/ml.
these are known as macrodrips
 The more commonly used metrisets
deliver 60/drips/ml. These are known as
microdrips.

IV calculation

For drops per minute the rule is:
Rate (drops/minute) = Volume (in ml) x
Time (minutes)
Drip factor
Example 1
A 1L bag of N/saline is to run over 6 hours. You are using a giving
set which delivers 20 drops/ml. What should the flow rate be set at?
Rate = 1000 x 20
convert the 1L to 1000ml
6 x 60
1
= 1000 x
20 common factor 10 & 4
360
1
= 2000
36
= 500
Long division
9
•
= 55.55
= 56 drops/ minute Rounded up to nearest whole number
Example 2

A 500ml bag of Hartman’s solution is to
run over 4 hours. The giving set delivers
20 drops/ml. What should the flow rate
be?
Solution – Example 2
Rate = 500 x 20
4 x 60
1
= 500 x 20
240
1
= 500
12
= 125
3
= 42 drops/minute
Example 3

A patient is to receive 500ml of 5%
Dextrose over 2 hours using a giving set
which delivers 20 drops/ml. Calculate the
drip rate in drops/minute.
Solution - Example 3
Rate =
500
x 20
2 x 60
= 10000
120
= 250
3
= 83 drops/minute
Example 4

A patient has to have an IV set up to
deliver 1L of fluid over 4 hours, using a
metriset (60 drops/ml). What should the
flow rate be?
Solution - Example 4
Rate =
1000 x 60
4 x 60
= 60000
240
= 2000
8
= 250 drops/minute
Example 5

A dehydrated adult is ordered 1L of
normal saline over 2 hours, using a
macrodrip (20 drops/ml) IV giving set.
Calculate the drip rate in drops/minute.
Solution - Example 5
Rate =
1000 x
20
2 x 60
= 20000
120
= 1000
6
= 167 drops/ minute
IV calculations
You made need to calculate how long an
IV infusion will take to run through, if you
know the drip rate re-organise the
previous rule
 For the time for a drip to run the rule is:


Time (in minutes) = Volume (in ml)
Rate (drops/min)
x Drip factor
Example 1

There is 500ml left to run through the IV
metriset. The drip rate has been set at
50 drops/minute. How long will it take to
run through?

Time (in minutes) = 500 x 60
50
1
= 10 x 60
1
1
= 600 minutes
= 10 hours
Example 2

There is 700ml of N/saline left to run
through the IV metriset. The drip rate is
set at 40 drops/minute. How long will it
take to complete?
Solution - Example 2
Time (in minutes) = 700 x 60
40
1
= 700 x 6
4
1
= 700 x 3
2
1
= 2100
2
= 1050
=17 ½ hours
= 17 hours 30 minutes
Example 3

How long will an IV take to run through if
the drip rate is set at 80 drops/minute
and there are 300ml left using a drip
factor of 20 drops/ml?
Solution - Example 3
Time (in minutes) =
=
=
=
OR =
300 x 20
80
6000
80
600
8
75 minutes
1 ¼ hr
Example 4

How long will 300ml of IV packed cells
take to run through at 30 drops/minute
using a blood giving set (15 drops/ml)?
Solution - Example 4
Time (in minutes) =
=
=
=
OR =
300 x 15
30
4500
30
450
3
150 minutes
2 ½ hr
Example 5

How long will 2l of Normal Saline take if
it is running at 100ml/hour using a
metriset?
Solution - Example 5
Time (in minutes) =
2000 x 60
100
= 120000
100
= 1200 minutes
OR = 20 hours
IV Calculations
Sometimes you made need to calculate
the hourly volume of an IV. To do this
reorganise the previous rule
 For volume per hour the rule is


Volume per hour = Total Volume
Time (hours)
Example 1
The doctor has ordered 1500 ml of fluid
to be given over 5 hours. What should
the hourly volume be in ml per hour?
 Volume = 1500
5
= 300 ml/hr

Example 2

The client is ordered 1.2L of Hartmann’s
solution over the next 6 hours. What
should be the hourly volume in ml/hour?
Solution - Example 2

Volume = 1200
6
= 200 ml/hr
Example 3

An IV containing 600ml has to run
through in the next 4 hours. What
volume needs to run through every
hour?
Solution - Example 3
Volume =
600
4
= 150 ml/hr
Example 4

A client’s IV is commenced at 1000HR. It
contains 1L and is to run through by
2000HR. What should the hourly volume
be (in ml per hour)?
Solution - Example 4
Volume = 1000
10
= 100 ml/hr
Example 5

What volume is needed every hour if a
client must have 700 ml in 10 hours?
Solution - Example 5
Volume = 700
10
= 70 ml/hr
Paediatric Drug Doses

Clarke’s Body Weight Rule (used for children
aged 1 and over)
Child’s dose = Weight of child (kg) x Adult
dose
Average adult weight (70kg)
Example 1
A child weighing 7kg is to be given
ampicillin. The adult dose is 500mg. How
much should the child be given?
 Child’s dose = 7
x 500
70
= 1
x 500
10
= 50 mg

Example 2

A child weighing 10 kg is to have
penicillin and the adult dose is 500mg.
How much would you give?
Solution - Example 2
Child’s dose =
=
=
=
=
10
x
70
1
x
7
500
7
71.4
71 mg
500
500
Paediatric Drug Doses

Clark’s Body Surface Area (BSA) Rule

Child’s dose = Surface area of child (m²) x Adult dose
average surface area of
adult (1.7 m²)
Example 1

A child whose BSA is 0.7 m², is ordered
penicillin. The adult dose is 1g. Calculate how
much to give.
Child’s dose = 0.7 x 1000
1.7
= 7
x 1000
17
= 7000
17
= 412 mg
Example 2

A child whose BSA is 0.6 is ordered
pethidine. The adult dose is 100 mg.
How much would you give?
Solution - Example 2

Child’s dose = 0.6 x
1.7
= 6
x
17
= 600
17
= 35 mg
100
100
Paediatric Drug Doses

Freid’s Rule (used for infants under 1yr old)
Child’s dose = Age in months
150
x
Adult dose
Example 1

A six month old child is to be given amoxycillin with
clavulanic acid (Augmentin). The adult dose is 500mg.
How much should the child be given?
Child’s dose = 6 x 500
150
= 6 x 10
3
= 60
3
= 20 mg
Example 2

A 4 month old is to be given tetracycline.
The adult dose is 250mg. How much
would you give?
Solution - Example 2
Child’s dose =
4 x 250
150
= 4
x 5
3
= 20
3
= 6 .6666
= 7 mg
Paediatric Drug Doses

Young’s Rule (used for children aged 2 to
12)
Child’s dose = Age in years x Adult dose
age + 12
Example 1

The adult dose for metronidazole (Flagyl) is 500mg.
How many milligrams should you give a 10 year old?
Child’s dose = 10
x 500
10 + 12
= 10
x 500
22
= 5000
22
= 227 6/22 mg
= 227 mg
Example 2

An 8 year old is ordered ampicillin. The
adult dose is 500mg. How much should
you give the client?
Solution - Example 2
Child’s dose =
=
=
=
=
8
x
500
8 + 12
8
x 500
20
8
x 50
2
4 x 50
200mg