calculating heparin bolus dosage and iv rate rule 18-6 rule 18-6 to determine the rate (ml/h) at...
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Calculating Heparin Bolus Dosage and IV Rate
Rule 18-6Rule 18-6 To determine the rate (mL/h) at which to administer a solution containing heparin, find A, where
D = rate of the desired dose
Q = dosage unit
H = dose on hand
A = amount to administer
.
IV and Bolus Heparin Calculations
Ordered: 1000 units/h IV heparin using an infusion pump
On hand: 25,000 units heparin in 500 mL D5W
H = 25,000 units; Q = 500 mL; D = 1000 units/h
Step A No conversion is needed.
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IV and Bolus Heparin Calculations –
Dimensional Analysis
Step B Calculate
A mL/h = 500 mL / 25,000 units x 1000 units / 1 hr
A mL/h = 500,000 mL/ 25,000 hr
A mL/h = 20 mL / h
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IV and Bolus Heparin Calculations
Step C Think!…Is It Reasonable?
Since the dosage strength of a 25,000 unit / 500 mL solution is 50 units / 1 mL, and 50 x 20 is 1000, it is reasonable.
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IV and Bolus Heparin Calculations (cont.)
• To ensure the maximum and/or safe dose is not exceeded
– determine the hourly dose of a heparin infusion.
IV and Bolus Heparin Calculations (cont.)
Rule 18-7Rule 18-7 To calculate the hourly dose (D), determine the following:
H = dose on hand or total amount to administer
Q = dosage units for total amount
A = amount to administer or flow rate of infusion
IV and Bolus Heparin Calculations
What is the hourly dose? Ordered: 25,000 units of IV Heparin in 500 mL to D5W to
infuse at 1000 units/h
H = 25,000 units; Q = 500 mL; A = 25 mL/hD = ? (hourly or desired dose)
Step A No conversion is needed.
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IV and Bolus Heparin Calculations – Proportion Method
Step B CalculateH = 25,000 units; Q = 500 mL; A = 25 mL/h
25,000 units : 500 ml = D : 25 ml/h
500 x D = 25,000 units x 25 1 /h
500D/500 = 625,000 units 1/h/500
D = 1250 units/h
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IV and Bolus Heparin Calculations – All Methods
Step C Think!…Is It Reasonable?
The dosage strength of 25,000 units / 500 mL provides 50 units /1 mL, and 50 x 25 = 1250.
It is reasonable.
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IV and Bolus Heparin Calculations
Determine if 1500 units / h is a safe dose.
1250 units/1 hr x 24 h/1 day = 30,000 units/day
Safe dose range for 24 h is 20,000 to 40,000 units.
So 30,000 units per day is a safe dose.
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Practice
What is the hourly dosage for an infusion of 45,000 units heparin in 1200 mL of D5W infusing at 30 mL/h? Is this a safe dose?
A = 1125 units/h
Is this a safe dose?
This is a safe dose.
IV and Bolus Heparin Calculations (cont.)
• Heparin protocol– Preprinted order set to guide administration of
IV heparin based on:• weight• serum activated partial thromboplastin time (aPTT)
– Bolus • initial dose given to achieve therapeutic blood level
of heparin
IV and Bolus Heparin Calculations (cont.)
• Heparin protocol
– Maximum dose is provided.
– Infusion rate and subsequent changes are based on weight in kilograms.
IV and Bolus Heparin Calculations
Calculate initial bolus dose of 80 units /kg (maximum dose: 8,000 units).
Patient weight = 154 lb
Step A Convert patient weight.
1 kg/2.2 lb = x/154 lb
2.2 x x = 154 X 1 kg
x = 154 / 2.2
x = 70 kg
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IV and Bolus Heparin Calculations – Proportion Method
Step B Calculate bolus dose using Proportion Method.
80 units: 1 kg = A : 70 kg
1 x A = 80 units x 70
A = 5600 units
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IV and Bolus Heparin Calculations – Formula Method
Step B Calculate amount to administer.
H = 1000 units Q = 1 mL D (bolus) = 5600 units
5.6 x 1 mL = 5.6 mL = A
ExampleExample
A mL x1units 1000
units 5600
IV and Bolus Heparin Calculations
Step C Think!…Is It Reasonable?
Desired dose of 5600 units is 5.6 times larger than dose on hand (1000 units).
It is reasonable!
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IV and Bolus Heparin Calculations (cont.)
Rule 18-8 Rule 18-8 To find the heparin flow rate based on weight:
1. Convert the weight to kilograms.
2. Determine desired dose.
3. Calculate amount to administer.
4. Calculate flow rate.
IV and Bolus Heparin Calculations – Weight-Based
Patient’s weight: 70 kg
Desired dose: (D/h) 18 units/kg/h
Dosage strength (H/Q) 25,000 units/500 mL
Step A: Weight is in kg, so no conversion is needed.
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IV and Bolus Heparin Calculations – Weight-Based
Patient’s weight: 70 kg
Desired dose: (D/h) 18 units/kg/h
Dosage strength (H/Q) 25,000 units/500 mL
Step B Calculate desired dose:
18 units: 1kg = D : 70 kg
1 x D = 18 units x 70
D = 1260 units / h
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IV and Bolus Heparin Calculations – Weight-Based
Step C Think!…Is It Reasonable?
1260 units / h is less than maximum dosage of 1800 units / h listed on the protocol.
It is reasonable.
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IV and Bolus Heparin Calculations (cont.)
Patient’s weight: 70 kg
Desired dose: (D/h) 1260 units / h
Dosage strength (H/Q): 25,000 units/500mL or
50 units/mL
Step A Convert units/h to mL/ h.
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IV and Bolus Heparin Calculations (cont.)
Step B Calculate flow rate.
H/Q = D/A
50 units/1 mL = 1260 units/h/A
1 mL x 1260 1/h = 50 x A
1265 mL/h/50 = 50A/50
A = 25.2 mL/ h
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IV and Bolus Heparin Calculations (cont.)
Loading dose = 5600 units administered as 5.6 mL IV push using a heparin concentration of 1000 units/mL.
The infusion will be started at 1260 units/h which is 25.2 mL/h using a heparin concentration of 25,000 units/500 mL.
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IV and Bolus Heparin Calculations (cont.)
Step C Think!...Is It Reasonable?
Verify rate by finding mL/h of 1 unit/kg/h and multiplying it by 18 (desired rate).
1 units/kg/h = 70 units/h
70 units/h = 1.4 mL/h
1.4 mL/h x 18 =25.2 mL/h
The infusion rate is reasonable.
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IV and Bolus Heparin Calculations –
Weight-based Adjustment
Infusion at 25.5 mL/h
aPTT result is 120 sec, so rate must be decreased by 2 units/kg/h
Volume for 1 u/kg/h = 1.4 mL/h
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IV and Bolus Heparin Calculations –
Weight-based Adjustment
Multiply by number of units of rate change.
1.4 ml/h x 2 (2 units/kg/h) = 2.8 mL/h
Subtract 25.2 mL/h – 2.8 mL/h
New infusion rate = 22.4 mL/h
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Practice
Patient’s weight: 75 kg
Desired dose: (D/h) 18 units/kg/h
Dosage strength (H/Q) 25,000 units heparin /500 mL (50 units/1 mL)
What is the desired dose?
What is the flow rate?
ANSWER: 1350 units / h
ANSWER: 27 mL/ h