iv administration – dosage calculation keith rischer, rn
TRANSCRIPT
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IV Administration – Dosage Calculation
Keith Rischer, RN
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Alternate Methods Dosage Calc.
Formula Ratio proportion Dimensional analysis
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IV solutions
Administered in plastic bags/bottles Administered continuously and/or
intermittently Components:
Water Glucose(dextrose) Saline Electrolytes Salts
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IV solutions
Labeled Letters – 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
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IV Solution Label
Calculate components: D5 0.45% NS in 1000
mL
D10 ¼ NS in 500 mL
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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
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Calculating Flow Rates IV Pumps
Total mL ordered = mL per hour Total hours ordered
Vancomycin 1000 mg (250 mL) IV over 2 hours by infusion pump
Vancomycin 750 mg (250 mL) IV over 1.5 hours
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IV Flow Rate in mL per hour: Infusion Rate is less than 1 hour
Total mL ordered X 60 min/hr = mL/hrTotal 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
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Setting Flow Rates for Manually Regulated IVs
Adjusting the rate by hand Counts drops per minute Use the roller clamp to adjust rate
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Calculating flow rates - ManuallyFormula 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
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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
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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
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Drop Factor Constants
Drop Factor Drop Factor Constant
10 drops per mL
15 drops per mL
20 drops per mL
60 drops per mL
610
60
415
60
320
60
160
60
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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
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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
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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
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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 Almost half of total volume infused in one-
quarter the time 21
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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
Patient would require close assessment for fluid overload
21
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Calculation of IV Flow Rate Adjustment
Remaining volume
Remaining hours
V
TC
40 mL
60 min60 gtt per mL
300 mL
7.5 h40 mL per hour
1
1
40 gtt per min
Adjusted flow rate
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Calculation of IV Flow Rate Adjustment
Adjusted gtt per min – ordered gtt per min
Ordered gtt per min
40 – 50 = -10 = -0.2 = - 20%
50 50
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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 many gtts/15 seconds…1 gtt every __ secs. After 5 hours only 300 mL has infused. The
IV is behind schedule. Calculate the new flow rate. Is this new rate acceptable?
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IV Push Injections
Use same calculations as other parenteral injections
IMPORTANT – Follow manufacturer or hospital guidelines for rate of administration
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IV Push Rate Calculation
XQH
D
Dosage Desired
Supply Dosage Recommended
Quantity (available form)
IV Push Rate Time
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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”
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Calculation of IV Push Rate
How much Furosemide should you prepare? Step 1. Convert
No conversion is necessary Step 2. Think
You want to give more than 1 mL
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Calculation of IV Push Rate
How much Furosemide should you prepare?Step 3. Calculate
mL 4 mL 1mg 10
mg 40Q
H
D
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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
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Calculation of IV Push Rate
How much should you infuse every 15 seconds? Push Factor Constant
4 per minute15 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
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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?
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