IV Administration – Dosage Calculation Keith Rischer, RN.

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 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

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 = 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

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

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 - 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

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 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

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 Almost half of total volume infused in one-

quarter the time 21

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

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

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

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?

IV Push Injections

Use same calculations as other parenteral injections

IMPORTANT – Follow manufacturer or hospital guidelines for rate of administration

IV Push Rate Calculation

XQH

D

Dosage Desired

Supply Dosage Recommended

Quantity (available form)

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 1. Convert

No conversion is necessary Step 2. Think

You want to give more than 1 mL

Calculation of IV Push Rate

How much Furosemide should you prepare?Step 3. Calculate

mL 4 mL 1mg 10

mg 40Q

H

D

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 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

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?