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Math for the Pharmacy Technician: Concepts and Calculations

Chapter 8: Chapter 8: Intravenous Intravenous CalculationsCalculations

Egler • Booth

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Intravenous Calculations

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Learning Objectives

Identify the components and concentrations of IV solutions.

Calculate IV flow rates. Calculate infusion time based on

volume and flow rate.

When you have successfully completed Chapter 8, you will have mastered skills to be able to:

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Learning Objectives (con’t)

Calculate infusion completion time based on flow rate.

Calculate volume based on infusion time and flow rate.

Calculate medications for intermittent IV infusions.

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IntroductionIntroduction

Intravenous (IV) fluids are solutions including medication that are delivered directly into the bloodstream via a vein

Blood is also delivered by IV IV fluids have a rapid effect Are necessary during emergencies or

other critical care situations

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Replacement fluids Maintenance fluids KVO (Keep Vein Open) fluids Therapeutic fluids

IV Solutions-FunctionsIV Solutions-Functions

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IV Replacement FluidsIV Replacement Fluids Replace electrolytes and fluids lost due

to hemorrhage, vomiting, or diarrhea

Examples:Examples:

Whole blood

Nutrient solutions

Fluids to treat dehydration

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IV Maintenance FluidsIV Maintenance Fluids Maintain normal electrolyte

and fluid balance

Example:Example:

– Normal saline given during and after surgery

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IV KVO FluidsIV KVO Fluids

To keep the vein open (KVO or TKO)

Example:Example: 5% dextrose in water

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Therapeutic FluidsTherapeutic Fluids

• Deliver medication to the patient

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IV LabelsIV Labels

Solutions are labeled with The name of the

components The exact amount of the

components

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IV LabelsIV Labels (con’t)

In abbreviations for IV solutions: Letters identify the

component Numbers identify the

concentration

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IV LabelsIV Labels (con’t)

Example:Example:An order for 5% dextrose in

Lactated Ringer’s solution might be abbreviated in any of the following ways: D5LR D5LR 5% D/LR D5%LR

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Common AbbreviationsCommon AbbreviationsDW, H20SNS, NSS

RLLR

NS

Dextrose

Water

Saline

Normal Saline

Lactated Ringer’s

Ringer’s Lactate

Half Normal Saline Solution(0.45% NaCl)

(0.9% NaCl)

2

1

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IV ConcentrationsIV Concentrations

5% DextroseIt contains 5 g of dextrose per 100 mL.

Normal saline is 0.9% salineIt contains 900 mg, or 0.9 g, of sodium chloride per 100 mL.

½ Normal saline is 0.45% salineIt contains 450 mg, or 0.45 g, of sodium chloride per 100 mL.

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IV Concentrations IV Concentrations (con’t)(con’t)

IsotonicThey have no effect on the fluid balance of the

surrounding cells or tissues.

Examples:Examples: D5W, NS, LR

Fluid moves across the cell membrane into surrounding cells and tissues.

This movement restores the proper fluid level in cells and tissues of patients who are dehydrated.

Examples:Examples: 0.45% NS, 0.33% NaCI

Hypotonic

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Hypertonic

IV ConcentrationsIV Concentrations (con’t)

These solutions draw fluids from cells and tissues across the cell membrane into the bloodstream.

They are helpful for patients with severe fluid shifts such as those caused by burns.

Example:Example: 3% saline

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IV ConcentrationsIV Concentrations (con’t)

Patients with normal electrolyte levels are likely to receive isotonic solutions.

Patients with high electrolyte levels will receive hypotonic solutions.

Patients with low electrolyte levels will receive hypertonic solutions.

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CompatibilityCompatibility

Additives Medications, electrolytes, and

nutrients combined with IV solutions

Common additives: potassium chloride, vitamins B and C, and antibiotics

Come prepackaged in the solution or may need to be mixed

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CompatibilityCompatibility (con’t)

Before combining any medications, electrolytes, or nutrients with an IV solution, be sure the components are compatible.

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Incompatible CombinationsExamplesExamples Ampicillin + 5% dextrose in water Cefotaxime sodium + Sodium

bicarbonate Diazepam + Potassium chloride Dopamine HCl + Sodium bicarbonate Penicillin + Heparin Penicillin + Vitamin B complex Sodium bicarbonate + Lactated

Ringer’s Tetracycline HCl + Calcium chloride

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Calculating Flow Rates

To calculate flow rates in milliliter per hour, identify the following:

T

VF Use the formula method or dimensional analysis to

determine the flow rate in milliliters per hour.

VV (volume) is expressed in milliliters

TT (time) must be expressed in hours (convert the units when necessary using calculation methods)

FF (flow rate) will be rounded to the nearest tenth

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Review and Practice

Flow rate = 200 mL/h

Find the flow rate.

•Ordered: 500 mg ampicillin in 100 mL NS to infuse over 30 minutes

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Calculating Flow Rates for Manual Regulation

To determine the flow rate (f) in drops per minute:

1. Change the flow rate mL/h (F) to gtt(drops)/min (f) using the formula

wherewhere

F = the flow rate in milliliters/hour

C = the calibration factor of the tubing in drops per mL

60 = number of minutes in an hour

60

FxCf

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Review and Practice

Flow rate = 35 gtt/min

• Find the flow rate in drops per minute that is equal to 35 mL/hour using 60 gtt (Drops) /mL microdrop tubing.

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Infusion Time and Volume An order may call for a certain

amount of fluid to infuse at a specific rate without specifying the duration.

You will need to calculate the duration or amount of time the IV will take to infuse.

You may know the duration and flow rate and will have to calculate the fluid volume.

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Calculating Infusion Time

To calculate infusion time in hours (T),(T), identify the:

V V (volume) expressed in millilitersFF (flow rate) expressed in milliliters per

hourFractional hours by multiplying by 60

F

VT

Use this formula or dimensional analysis to find T, the infusion time in hours.

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Review and Practice

Total time to infuse the solution is 13 hours and 20

minutes

Find the total time to infuse.Ordered: 1000 mL NS to infuse at a rate of 75 mL/h

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Review and Practice

T = 6 hours = total time to infuse the 750 mL

Find the total time to infuse.Ordered: 750 mL LR to infuse at a rate of 125 mL/hr started at 11 p.m.

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Calculating Infusion CompletionTime

To calculate the time when an infusion will be completed, you must first know the time the infusion started in military time and the total time in hours and minutes to infuse the solution ordered.

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Calculating Infusion Completion Time (con’t)

Since each day is only 24 hours long, when the sum is greater than 2400 (midnight), you must start a new day by subtracting 2400.

This will determine the time of completion, which will be the next calendar day.

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Review and Practice

The infusion will be complete at 0500 or 5:00 a.m. on 08/05/05

Determine when the infusion will be completed.Ordered: 750 mL LR to infuse at a rate of 125 mL/hr, started at 11 p.m. on 08/04/05

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Calculating Infusion Volume

Use the formula V = T X F or dimensional analysis to find V the infusion volume in mL, where the

TT (time) must be expressed in hours FF (flow rate) must be expressed in

milliliters per hour

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Review and Practice

V=175 mL or the volume that will infuse over 5 hours

Find the total volume infused in 5 hours if the infusion rate is 35 mL/h.

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Review and Practice

V = 2400 mL = the volume that will infuse over 12 hours

Find the total volume infused in 12 hours if the infusion rate is 200 mL/h.

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Intermittent IV Infusion IV medications are sometimes

delivered on an intermittent basis Delivered through

IV secondary line Saline Heparin lock

Can be delivered with continuous IV therapy or when no continuous IV solutions are infusing

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Secondary Lines (Piggybacks or IVPB)

IV setup that attaches to a primary line Used to infuse medications or other

compatible fluids on an intermittent basis (such as q6h)

Uses shorter tubing IVPB bags are smaller: 50,100, or 150

mL

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Intermittent Peripheral Infusion Devices

Saline or heparin locks An infusion port attached to an

already inserted IV needle or catheter

Allow direct injection of medication or infusion of IV medications

Medications ordered as IV push or bolus

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Intermittent Peripheral Infusion Devices (con’t)

Since there is no continuous flow of fluids through the IV line you must flush the device 2 to 3 times per day to prevent blockage.

Saline lock -- is an infusion port attached to an already inserted catheter for IV access, flushed with saline.

Heparin lock -- is an infusion port attached to an already inserted catheter for IV access, flushed with heparin.

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Preparing and Calculating Intermittent Infusions

Flow rate is calculated for prepared medications the same as regular IV infusions.

Amount of fluid may be less and time to infuse may be less than an hour.

Calculate the flow rate you will need to change the number of minutes into hours.

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Preparing and Calculating Intermittent Infusions (con’t)

When preparing medications for an intermittent IV infusion:

Reconstitute the medication using the label and package insert.

Calculate amount to administer and the flow rate.

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Identify four functions of IV fluids.

Review and Practice

Answers:

1. Replacement

2. Maintenance

3. KVO

4. Therapeutic

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How many mg of sodium chloride is in 100 mL of normal saline?

Review and Practice

Answer: 900 mg NaCl

How many mg of sodium chloride is in 100 mL of 0.45% NS?

Answer: 450 mg NaCl

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Intravenous Calculations

THE END

As a pharmacy technician you will need to As a pharmacy technician you will need to know how to perform accurate IV know how to perform accurate IV

calculations.calculations.

Results can be fatal if the wrong Results can be fatal if the wrong medication or dosage is givenmedication or dosage is given