IV Administration – dosage calculation
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Transcript IV Administration – dosage calculation
IV Administration –
Dosage Calculation
Keith Rischer, RN
Alternate Methods Dosage Calc.
Formula
Ratio proportion
Dimensional analysis
IV solutions
Administered in plastic bags/bottles
Administered continuously and/or
intermittently
Components:
Water
Glucose(dextrose)
Saline
Electrolytes
Salts
IV solutions
Labeled
– solution components
Numbers – concentration
LR – Lactated Ringers
NS: Normal Saline 0.9% NaCl
D5W – 5% Dextrose in water
= 5 g dextrose / 100 ml solution
D5 NS with 20 mEq KCL
Letters
IV Solution Label
Calculate
components:
D5 0.45% NS in 1000
mL
D10 ¼ NS in 500 mL
Tonicity of IV Solutions
Hypotonic
Isotonic
Hypertonic
0.9 NS
D5W
LR
½ (0.45%) NS
¼ (0.225%) NS
D5 ½ NS
D5 NS
D5 LR
3% NS
Calculating Flow Rates IV Pumps
Total mL ordered
Total hours ordered
= mL per hour
Vancomycin 1000 mg (250 mL) IV over 2 hours
by infusion pump
Vancomycin 750 mg (250 mL) IV over 1.5 hours
IV Flow Rate in mL per hour: Infusion
Rate is less than 1 hour
Total mL ordered X 60 min/hr = mL/hr
Total min ordered
Order:
Ampicillin
500 mg IV in 50 mL NS over 30
minutes
Order:
Give
Amiodarone 150mg in 100 ml of D5W
over 10 minutes
Setting Flow Rates for Manually
Regulated IVs
Adjusting the rate by hand
Counts drops per minute
Use the roller clamp to adjust rate
Calculating flow rates - Manually
Formula method
V X C (gtt factor) = R
T
Volume (mL) X drop factor (gtt per mL)= Rate (gtt/min)
Time (min)
Physician orders: D5W IV at 125 mL/hr.
The IV infusion set is calibrated with a drop factor of 10 gtt/mL.
Calculate the IV flow rate
Physician orders: 0.9 NS IV at 75 mL/hr.
The IV infusion set is calibrated with a drop factor of 10 gtt/mL.
Calculate the IV flow rate
Calculating gtts per/minute
Once gtts/minute determined...
Divide
this total by a factor of 4
20
gtts/minute… 5 gtts every 15 seconds
12 gtts/minute… 3 gtts every 15 seconds
How
many gtts every 15 seconds?...
Divide the gtts determined by 15 (seconds)
This will be the seconds between each gtt
5
gtts every 15 seconds
– 15/5= x seconds
3
gtts every 15 seconds
– 15/3= x seconds
Calculation of Drops per min:
Microdrip Drop Factor
Volume (mL) X drop factor (gtt per mL)= Rate
Time (min)
Order:
D5 NS IV at 50 mL per h
Drop factor is 60 drops per mL
Calculate gtt/min
Drop Factor Constants
Drop Factor
10 drops per mL
Drop Factor Constant
60
6
10
15 drops per mL
60
20 drops per mL
15
60
4
3
20
60 drops per mL
60
60
1
Drop Factor Constants
Physician orders: D5W IV at 125 mL/hr
10
gtts/mL manual infusion set
125 mL=20.8 gtt/minute or 21 gtts
6
Physician orders: 0.9 NS IV at 75 mL/hr.
75mL=
6
Adjusting IV Flow Rate
Check for institutional policy regarding
correcting off-schedule IV rates and the
percentage of variation allowed
Variation should not exceed 25 percent
%
variation will be positive (+) if
administration is slow and rate has to be
increased
Negative () if administration is too fast
and rate has to be decreased
Adjusting IV flow rates
Follow three steps:
Remaining volume = recalculated mL/h
Remaining hours
V X C (gtt factor) = R
T
Adjusted gtt per min – ordered gtt per min = % variation
Ordered gtt per min
Calculation of
IV Flow Rate Adjustment
Order: 500 mL LR to run over 10 hours at
50 mL per hour
Drop
factor is 60 drops per mL and IV is
correctly infusing at 50 drops per min
After 2 hours, 300 mL is remaining
1
Almost
half of total volume infused in one2
quarter the time
Calculation of
IV Flow Rate Adjustment
IV infusion is ahead of schedule
Compute a new rate of 300 mL to
complete IV fluid order in remaining 7
hours
1
Patient would require close assessment2
for fluid overload
Calculation of IV
Flow Rate Adjustment
R em ain in g v o lu m e
R em ain in g h o u rs
V
T
C
40 m L
60 m in
1
300 m L
7 .5 h
4 0 m L p er h o u r
1
60 gtt per m L 40 gtt per m in
Calculation of IV Flow Rate Adjustment
Adjusted gtt per min – ordered gtt per min
Ordered gtt per min
40 – 50 = -10
50
50
= -0.2 = - 20%
Adjusting IV flow rates
The physician orders 1000 mL of D5
0.45% NS at 100 mL per hour over 10
hours. Drop factor-10 gtt per mL
What
is the initial correct gtt/minute
How
After
many gtts/15 seconds…1 gtt every __ secs.
5 hours only 300 mL has infused. The
IV is behind schedule. Calculate the new flow
rate. Is this new rate acceptable?
IV Push Injections
Use same calculations as other parenteral
injections
IMPORTANT – Follow manufacturer or
hospital guidelines for rate of
administration
IV Push Rate Calculation
Dosage Desired
Quantity (available form)
D
Q X
H
Supply Dosage Recommended
IV Push Rate Time
Calculation of IV Push Rate
Order: Furosemide (Lasix) 40 mg IV Push
stat x1
Supply: Furosemide 10 mg per mL with
drug literature guidelines of “IV infusion
not to exceed 20 mg over 1 minute”
Calculation of IV Push Rate
How much Furosemide should you
prepare?
Step
No
Step
1. Convert
conversion is necessary
2. Think
You
want to give more than 1 mL
Calculation of IV Push Rate
How
much Furosemide should you
prepare?
Step
D
H
3. Calculate
Q
40 mg
10 mg
1 mL 4 mL
Calculation of IV Push Rate
What is a safe infusion time?
Use the formula:
D X Q =X
H
40 mg X 1 min = 2 minutes
20 mg
Calculation of IV Push Rate
How much should you infuse every 15 seconds?
Push Factor Constant
4 per minute
15 seconds = 1/4
60 seconds
4
mL over 2”
Push factor is 8 (4x2”=8)
Volume
4 mL=0.5 mL push every 15 seconds
Push Factor
8
Calculation of IV Push Rate
Order: Dilantin 100 mg IV now
Supply:
Dilantin 50 mg per mL with drug
literature guidelines of “the infusion rate
should not exceed 50 mg per min”.
How much should you prepare?
What is safe infusion time?
How much should you infuse every 15
seconds?