Modern metric measurements have almost completely replaced an old English imprecise Apothecary system ^* in order to reduce medication errors. The modern metric system is logical, precise, and easy to work with because it’s a standardized decimal measurement system using multiples (powers) of 10 similar to our monetary structure which is also based on a decimal structure. With a little practice and repetition, nurses will be very comfortable with it.

It has been adopted by most countries of the world for standardized weights and measurements. Known as the International System of Units (SI), it is the modern form of the former French metric system. It is required for admission to the European Union. Resistance to change and expense involved have slowed the U.S. “metrication” progress except in the scientific community.

This chapter focuses on understanding and interpreting the metric measurements used in medication orders and records, on medication labels, in laboratory reports, and nursing practice. It also includes examples of household measurements. Household measures are used for some medications taken at home, primarily liquids. Nurses need to know the metric-household equivalents for home care practice, for patient and family discharge and home-care teaching. Teaspoon A does not equal teaspoon B.

ESSENTIAL Vocabulary

Base Units of Metric Measurement Three base units are commonly used for metric measurement of medications to indicate weight (or mass), volume, and length: gram (g), liter (L), and meter (m).

Memorize these base units of measurement. The abbreviation for liter is preferably capitalized, L, to avoid confusion with the number 1.

Household System of Measurement Utensils used in the home, such as cups, teaspoons, tablespoons, droppers, etc. Their use can create a safety risk for measuring medication doses because of inconsistent capacities.

ISMP Institute for Safe Medication Practices, a non-profit organization that educates the health care community and consumers about safe medication practices.

Modern Metric System A popular name for the International System of Units (SI). Modified and adopted for uniform measurement in most countries, now recommended for all medication doses in the US by TJC and by ISMP.

SI Units SI Units in the metric system refer to a dimension, such as weight (or mass), volume, and length. Examples of metric units of measurement include kilogram (kg), microgram (mcg), milligram (mg), gram (g), liter (L), and meter (m). Write out the words unit and units; do not use abbreviations such as U.

TJC The Joint Commission, a national non-profit independent agency dedicated to improved quality of health care through the provision of accreditation and certification to health care organizations with an emphasis on high standards and patient safety including medication administration safety.

RAPID PRACTICE 3-1 Vocabulary Review

Estimated completion time: 10-15 minutes Answers on page 492

Directions: Study the vocabulary and write the answers in the space provided.

1. What are the three base units of the metric system? __________________________

2. Why is the symbol for liter capitalized? ________________________________

3. What is one problem with using household utensils for medication doses? ________________________________

4. What system of measurement is currently used for most medication doses in the United States? ________________________________

5. What are the abbreviations for two organizations which address safe medication practices? ________________________________

Metric Equivalent Chart

Weight	Volume
1000 mcg (micrograms) = 1 mg (milligram)	1000 mL (milliliter) = 1 L (liter)
1000 mg = 1 g (gram)
1000 g = 1 kg (kilogram)
	Length
lb to kg conversion	10 mm (millimeters) = 1 centimeter (cm)
2.2 lb (pound) = 1 kg	100 cm = 1 meter (m)
inch to cm conversion	1000 mm = 1 meter (m)
1 inch = 2.5 cm (approximate)	1000 mm = 1 meter (m)

Metric Measurements: Base Units

Three base units are commonly used in the medical field. Two are used mainly for medication doses (gram and liter) and one (meter) is used occasionally for topical medications.

Memorize these three base units.

Base Units

Dimension	Metric Base Unit	Approximate English System Equivalent
Weight (or mass)	gram (g)	About 130 ounce dry weight
Volume	liter (L)	About 4 measuring cups, a little more than a quart
Length	meter (m)	About 39 inches, a little more than a yard

The abbreviation for the base unit liter is capitalized (L) to avoid misreading as the number 1. The base units abbreviations for gram (g) and meter (m) are written in lowercase letters. No other abbreviations are authorized.

Q: Ask Yourself

1. What are the three base units of metric measurement used for medications and their abbreviations?

_________________________________________________________________________

A: My Answer

Metric Units Number Line

The following metric units number line illustrates the relationship of the values for selected metric prefixes.

Metric Prefixes and Values

Four prefixes are commonly used for medication dose calculations:

• centi (meaning hundredth)

• milli (meaning thousandth)

• micro (meaning millionth)

• kilo- (meaning a thousand times)

• A fifth prefix, deci- (meaning tenth), is used in laboratory reports.

Memorize the prefixes and meanings.

Study Table 3-1, and note the numerical values and relationships. Metric prefixes are combined with bases to create new quantities, as shown in the examples in the table.

TABLE 3-1

Metric Measurements, Prefixes, Values, and Meaning

Prefix	Multiplier	Exponential Power of 10	Meaning	Examples	Meaning
micro (mc)	.000001	10⁻⁶	millionth part of	microgram (mcg)	one millionth of a gram
milli (m)	.001	10⁻³	thousandth part of	milliliter (mL)	one thousandth of a liter
milli (m)	.001	10⁻³	thousandth part of	milligram (mg)	one thousandth of a gram
centi (c)	.01	10⁻²	hundredth part of	centimeter (cm)	one hundredth of a meter
deci- (d)	.1	1 0⁻¹	tenth part of	deciliter (dL)	one tenth of a liter
kilo- (k)	1000	10⁻³	1000 times	kilogram (kg)	one thousand grams

Note: The prefix value never changes when combined with a base unit (e.g., the prefix milli [m] = 001).

1 mm = 0.001 (one thousandth of a meter).

1 mL = 0.001 (one thousandth of a liter).

1 mg = 0.001 (one thousandth of a gram).

Q: Ask Yourself

1. What are the numerical values of the prefixes m, c, d, and k?

_________________________________________________________________________

A: My Answer

• For review, write out the five prefixes and three base units used for medication administration. Learn them in preparation for analyzing medication orders.

Prefixes and Abbreviations	Base Units and Abbreviations
1. ____________________________ 2. ____________________________ 3. ____________________________ 4. ____________________________ 5. ____________________________	1. ____________________________ 2. ____________________________ 3. ____________________________

The abbreviation for the prefix micro (mc) is preferred over the Greek letter mu (μ) in handwritten patient medical records. A handwritten μg (microgram) can be mistaken for mg (milligram).

CLINICAL RELEVANCE

It is very important to recognize the μ and distinguish it from zero and from mg. Either misinterpretation could lead to serious errors in medication dosage. The nurse should clarify the meaning of unfamiliar symbols and words with the prescriber.

RAPID PRACTICE 3-2 Writing Metric Units and Abbreviations

Estimated completion time: 10 minutes Answers on page 492

Directions: Study the metric units and abbreviations. Write the metric name and abbreviation in the space provided.

1. Write the name and abbreviation for the prefix that means 11000. __________

2. Write the name and abbreviation for the prefix that means 1100. _______

3. Write the name and abbreviation for the prefix that means 11,000,000. _______

4. Write the name and abbreviation for the prefix that means 110. _______

5. Write the name and abbreviation for the prefix that means 1000 times. _______

6. Write the name and abbreviation for the base unit of volume. _______

7. Write the name and abbreviation for the base unit of length. _______

8. Write the name and abbreviation for the base unit of weight, or mass. _______

9. Write the name for the base unit m. _______

10. Write the name for the prefix m. _______

Metric Notation

Writing metric unit combinations and equivalents

Study the example and note the correct order of writing as follows:

1. Numeral or numerals

The following are examples of correctly written metric quantities: 100 mg, 1000 mL, 10 L, 250 cm, 2500 mcg, and 1,000,000 kg.

Do not write an m to look like a w or a u.

Do capitalize L for liter.

Metric abbreviations are case sensitive.

Do not close up a c so that cm looks like am.

Do use commas to group numbers with more than three consecutive zeros in groups of three from right to left.

Do not make up your own metric abbreviations

Do not pluralize metric abbreviations.

Guide to Metric Notation	Examples
Abbreviations are always used when accompanied by a number. The number, followed by a space, precedes the abbreviation.	10 mg, 2 g, 5 L
	Metric terms are written out when unaccompanied by a number, as illustrated in the following sentence: “Write out grams and milligrams.”
When the number of units following the slash meaning per is 1, the number 1 may be omitted from the abbreviation. It is implied.	40 mg/ g (40 mg per 1 g)
Metric abbreviations are always singular. They are not pluralized.	Milligrams is abbreviated mg.
	Liters is abbreviated L.
	Write mg, not mgs; g, not gs; and L, not Ls.
There is no period after metric abbreviations except when they fall at the end of a sentence.	Give 2 mg, not 3 mg.
	He drank 2 L of water, followed by 1 L.