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?