Units of Measure

Math for Clinical Practice

Weight

• Kilogram = kg

• Gram = g

• Milligram = mg

• Microgram = mcg

Length

• 1 meter = m

• Centimeter = cm

• Millimeter = mm

Volume

• 1 liter = L

• 1 milliliter = mL or cc

(cc is not to be used anymore according to JACOH standards but it is a common error since it has been used for years)

CC = mL

Length

• 1 meter (m) = 100 cm or 1000 mm

• Centimeter (cm) = 10 mm

• Millimeter (mm) = 0.1 cm

Household Abbreviations

• 1 ounce or oz

• Tablespoon = Tbs

• Teaspoon = tsp or t

Conversion of Metric Units

Household Measurement

• 1 ounce (oz) = 30 mL

• 1 tablespoon (Tbs) = 15 mL

• 1 teaspoon (tsp) = 5 mL

Ounces to mL

• You are doing intake and output and the mother states the infant has consumed 3 ½ ounces of formula. How many mL has the infant consumed?

• 3.5 x 30 mL = 105 mL

• You would record 105 mL on the intake record

Measuring Liquids

Tablespoons

• You are teaching a geriatric patient how to measure her medications. She is to take 15 mL of liquid Maalox to aid digestion.

• You would instruct her to use what household measuring device to take her mediation?

• Teaspoon or tablespoon • She would take one tablespoon of

medication.

Teaspoon

• You are working with a mother of a toddler and she has been instructed to give the child 1 ½ teaspoons of medication. You are demonstrating how to give the medication with a syringe with measurements in mL.

• How many mL would you have her give?

1 Teaspoon = 5 ml

• 1 ½ teaspoons = 1.5 teaspoons

• 1.5 teaspoon x 5 mL = 7.5 mL

• You would have her draw up 7.5 mL in a po syringe.

Nursing Alert

• Remember if there is not a number to the left of the decimal point a zero is placed there to highlight the decimal point placement.

• Correct: 0.5 mL or 0.25 g

• Incorrect: 5.0 mL or 25.0 g

Nursing Alert

• Decide whether you are converting from smaller unit to larger unit or larger unit to smaller unit.

Liter to milliliters

• 1 liter (L) = 1000 milliliters (mL)

• 1.2 L = ___________

• 1.2 x 1000 = 1200 mL

Milliliters (mL) to Liters (L)

• Change mL to Liter (L)

• mL is smaller than a liter

• Move decimal point three places to the right

• 750 mL = 0.75 L

Metric Units Weight

• Kilogram = kg

• 1 kg = 1000 grams (g)

• 1 gram (g) = 1000 milligrams (mg)

• 1 milligram (mg) = 1000 micrograms mcg

How to calculate kilograms

• Remember you will weigh less in kilograms

• To convert pounds to kilogram you divide by 2.2

• Convert 100 pounds to kg

• 100 / 2.2 = 45.454 or 45.45

• In the infant / small child carry out to the 100th or two decimal places.

Example

• Convert the following metric measurement:

• 0.2 mg = ______ g.

• (gram is larger than a mg)

• Need to move the decimal 3 places or divide by 1000.

• Answer 0.2 mg = 0.0002 g

Example

• 100 mcg = ______ mg

• You are going from a smaller unit to a larger unit.

• You would move the decimal point 3 places or divide by 1000.

• 100 mcg = 0.1 mg

International and Milliequivalent Measures

International Units

• Heparin, insulin, penicillin, epoetin products (Epogen, Procrit) are measured in international units.

• Example: regular insulin 10 units SQ in am

• Example: penicillin 600,000 units IM x one dose

Milliequivalent Measures

• Do not confuse with milligrams.

• Notation is mEq

• Milliequivalent measures the number of grams of equivalent weight of a drug contained in 1 mL of normal saline.

mEq

• Common drugs: sodium bicarbonate, sodium chloride, potassium chloride.

• Examples:

• 10 mEq of potassium chloride to ½ L of IV solution

• 15 mEq of sodium chloride to 1 L of IV solution

Conversions

Conversions

• Clinical connection: often you need to calculate between different systems of measure.

Metric System

• Metric System

• 1 kg = 1000 g

• 1 g = 1000 mg

• 1 mg = 1000 mcg

• 1 L = 1000 mL

Grains

60 mg = 1 gr

45 mg = ¾ gr

30 mg = ½ gr

15 mg = ¼ gr

10 mg = 1/6 gr

Conversion to Metric Equivalents60 mg

gr1

15 mggr 1/4

30 mg

gr 1/2

45 mg Gr 3/4

Practice Problems

• gr ¾ = ___________ mg

• gr ¼ = ___________ mg

• gr 15 = ___________ mg

• 300 mg = _________ gr

• 60 mg = __________ gr

• 30 mg = __________ gr

• gr 1/6 = ___________ mg

Practice problems

• The bottle of Tylenol states that you are to give X (ten grains) of Tylenol.

• How many mgs are you giving ________

Chapter Review

Calculations in the Clinical Setting

Ratio – Proportion Method

• Using the ratio proportion method offers a systematic approach to solving clinical math calculations.

The Set-up

• Solving the unknown

• The cookies and the eggs

• If the recipe states you need 2 eggs to make 2 dozen cookies. How many eggs do you need to make a dozen cookies?

• 24 cookies 12 cookies

• 2 eggs = x eggs

Practice Problem

• Page 106

• Lorazepram 3 mg IV every 6 hours as needed.

• Lorazepam is supplied as 4 mg / mL

The set-up

• 4 mg3 mg

• 1mL = x mL

• (cross multiply)

• 3 / 4 x = 0.75 mL

• You would draw up 0.75 mL to equal 2 mg of Lorazepam

Practice Problem

• Page 108

• Phenytoin sodium 300 mg by mouth at bedtime.

• Phenytoin sodium supplied as 125 mg / 5 mL.

The Set-up

• 125 mg 300 mg

5 mL = x mL

(Cross multiple) (X is on the bottom)

1500

125 X = 12 mL equals 300 mg of the drug

Practice Problems

• Remember to label properly and put the x on the bottom.

Body Weight

Review

• Pounds to kilograms

• Pounds divided by 2.3

• Practice problems 1-10 page 140-41

Practice Problem

• Neupogen 5 mcg/kg/day IV over 30 minutes.

• Patient weight = 174

Change Pounds to Kilograms

• 174 / 2.2 = 79.09 kg

Determine the dosage

• 5 mcg / kg / day

• 5 mcg x 79.09 (weight in kg) = 395.45 mcg per dose

• Drug is rounded to 395 mcg per dose to be added to 50 mL of Dextrose 5% in Water.

Practice Problem

• Phenobarbital 30 – 120 mg / kg per day in 3 divided doses

• Physician orders the maximum dose or 120 mg / day to be given q 8 hours.

• 1st you would need to divide 120 mg by 3 doses = 40 mg per dose

Determine the Amount

• Phenobarbital is provided as 65 mg / mL• For one dose you would need to draw up

how much of the medication?• 40 mg = 60 mg x mL 1 mL

40 mg = 0.66 mL 60 x