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Slide 1
Slide 2
Med Math The basics use like units use common sense find a
formula/system that works for you
Slide 3
Making weight.. 1 kilogram (kg) = 2.2 pounds (lb) Actual
conversion Wt: 220 lb 220 divided by 2.2 = 100kg 10% or Midnight
rule Half of 220 = 110 10% of 110 = 11 Subtract 11 from 110 =
99kg
Slide 4
Metric conversions 1 gram (g) = 1000 milligrams (mg) 1 mg =
1000 micrograms (mcg) 1 liter (L) = 1000 milliliters (ml) You need
to give 500 mcg. How many mg? Mg - move decimal 3 places to the
left = 0.5 mg OR 500 = half of 1000 so half of 1 =.5 mg You need to
give 100 mg. How many mcg? How many g? mcg - move decimal point 3
places to the right = 100,000 mcg g - move decimal point 3 places
to the left = 0.1 g
Slide 5
Basic calculations Desired dose (D) Known dose on hand (H) x
Unit of measure or volume on hand (Q) = volume or unit of measure
to be administered (X) D X Q = X H
Slide 6
Example 1 You are ordered to give 5 mg Valium IV. The label
states there is 10 mg in 2cc (10mg/2cc). How many ccs will you
give? DD= 5mg Concentration = 10 mg Volume on hand = 2 cc Wight
conversion need = no Unit to be given= cc Formula #1 Desired Dose X
Volume on Hand = ___ml to be given Concentration 5 mg X 2 cc = 1 cc
You will give 1cc! 10 mg
Slide 7
Example 2 You are to give 0.5 mg/kg IV push. Your patient
weighs 80 kg. The drug comes packaged: 100mg/10cc. How many mg will
you give? How many ccs will you deliver? Your equation to determine
mg will look like this: 0.5 mg/kg x 80 kg = 40 mg to be given Your
equation to determine cc will look like this: DD= 0.5mg / kg
Concentration = 100 mg Volume on hand = 10 cc Wight conversion need
= yes 0.5 mg/kg x 80 kg = 40 mg to be given Unit to be given= cc
Formula #1 Desired Dose X Volume on Hand = ___ml to be given
Concentration 40 mg x 10 cc = 4cc 100 mg
Slide 8
Drip calculations Clock method (used only for 4:1 ratio) 4 3 1
60 15 30 45 2 If your dose is 1 mg/min, your drip rate is 15
gtt/min. If the order is greater than 4 mg/min, add them together.
A dose of 6 mg/min is 90 gtt/min (4 + 2 =6 so 60 + 30 = 90)
Slide 9
Drip calculations example 3 Formula 2 : IV bag volume (ml)
Desired Dose Admin Setup (gtt) ---------------------- --- X
--------------- ------ X ---------------------- = gtt/min
Concentration of Drug 1 min 1ml The order is for 5 mg/min. You have
a 500 cc bag of NS, a 60 gtt/cc administration set, and 2 g of drug
on hand. How many gtt/min will you administer? DD= 5mg
Concentration = 2 g = 2000 mg Volume on hand = 500 cc Wight
conversion need = no Unit to be given= gtt / min 5 mg x 500 cc (ml)
x 60 gtt/cc = 75 gtt/min 2000 mg x 1 min x I ml Note: If the dose
is weight based, determine the total dose prior to beginning the
equation or multiply everything by the number of kg.
Slide 10
Questions
Slide 11
To calculate drip rates / transfusion rates example 4 To
calculate the drip rate (drops / minute) Formula 3 # Drip Rate gtt
= Volume to be infused (ml) x Drop Factor (gtt/ml) min infusion
Time (minutes) 1 unit of blood is approximately 400ml in volume
E.g. A unit of blood is prescribed to run over 2 hours; The giving
set has a drop factor of 20 gtt /ml. What is the drip rate (drops
/min)?
Slide 12
Calculate the Transfusion rate example 5 E.g. A unit of blood
is prescribed to run over 4 hours; The giving set has a drop factor
of 20 gtt /ml. What is the drip rate (drops /min) ? Formula 3 #
Drip Rate gtt = Volume to be infused (ml) x Drop Factor (gtt/ml)
min infusion Time (minutes) Drip rate = 400 ml x 20 gtt Drip Rate
is drops 4 hour x1ml Thus Drip Rate = 400ml x 20 gtt x 1 hour 4
hour x 1 ml x 60 minutes By multidimensional analysis units are
correct (drops / minute) Drip Rate = 100 / 3 = 33 drops /
minute
Slide 13
Drop rate is rounded up or down to the nearest drop In the
clinical setting to be able to count drops / minute it is sensible
to have a number divisible by 4 - Thus you would set this drip at
32 drops per minute
Slide 14
Converting drip rate (gtt /min) to ml /hour Example 6. What is
the transfusion rate in ml /hour of a blood transfusion being run
at 40 drops / minute through a giving set with drop factor of 20
gtt / ml?
Slide 15
Formula 3 # Drip Rate gtt/ min = Volume to be infused (ml) x
Drop Factor (gtt/ml) infusion Time (minutes) 40gtt/min = volume to
be infused x 20 gtt /ml 60 min 40 gtt x 60 min = volume to be
infused x 20 gtt/ ml min Volume to be infused = 40 gtt x 60 min =
120ml /hr min x 20gtt/ml
Slide 16
exampl 7 : You are asked to run an intravenous infusion of
1litre of D5W over 6 hours. What drop rate will you set the
infusion at if the giving set has a drop factor of 10 gtt/ml?
Volume to be infused X IV Drip Set (gtt) = ____ gtt/min Time in
(min) 1ml =1000ml x 10 gtt 6 hours X 60 (mins) X 1ml = 1000 = 27.8
drops / min 36 Since we always round up or down to the nearest drop
the actual rate will be 28 drops / minute
Slide 17
Questions
Slide 18
example 8: You are asked to set up a 1litre normal saline
infusion to run over 10 hours. The giving set has a drop factor of
20 gtt / ml. what rate will you set the drip at in drops/minute?
Volume to be infused X IV Drip Set (gtt) = ____ gtt/min Time in
(min) 1ml = 1000ml x 20 gtt-------------- 10 hr X (60 min) X 1 ml =
100 = 33 drops / minute 3
Slide 19
example 9 : A 750ml infusion of 5% dextrose is infusing at
65gtt/min. The drop factor of the giving set is 60 gtt/ml. How long
will the infusion take? Volume to be infused X IV Drip Set (gtt) =
____ gtt/min Time in (min) 1ml 65 gtt/min = 750ml x 60 gtt X hr
x(60min)x 1ml X = 750 x 60 x 1 65 x 60 X = 11.5 hours
Slide 20
example 10 : A litre of normal saline is meant to be running
over 8 hours. The drip is set at 83gtt/min,the giving set has a
drop factor of 20gtt/ml. Volume to be infused X IV Drip Set (gtt) =
____ gtt/mi Time in (min) 1ml 83 drops = 1000ml x 20 gtt min X hr x
(60min)x 1 ml X hr = 20,000 = 20,000 = 4 hours 83 x 60 4980 Thus
you need to halve the drops /min to 42 drops / minute
Slide 21
example 11 : A litre of 5% dextrose is running at 80 gtt/min.
The drop factor is 60 gtt/ml. What will the pump be set at in
ml/Hr.
Slide 22
Formula 3 : 1000ml X 60 gtt =80 gtt /min time (?) 1ml Time =
1000 ml X 60 gtt/ml = 750 min = 750/60 = 12.5 hrs 80 gtt /min 1000
ml will be run in 12.5 hrs 1000 ml / 12.5 hrs = 80 ml / hr
Slide 23
example 12 : A heparin infusion is prescribed to run at 5000
units / Hr. The infusion is made up of 25,000 units in 500ml 5%
dextrose. What rate in ml/hr will you set the pump? Answer =
100ml/1 hr