copyright © 2008 thomson delmar learning systems of measurement metric / apothecary / household...

Copyright © 2008 Thomson Delmar Learning

Systems of MeasurementMetric / Apothecary / Household

Revised KBurger0808

Textbook Assignment:

Pickar, G. (2007). Dosage calculations: A ratio-proportion approach. (2nd ed.)Chapter 3


The Metric System

• The metric system is known for its simplicity. All units of measurement in the metric system are based on decimals—that is, units that increase or decrease by multiples of ten.

• JCAHO recommends that the metric system by used exclusively for ordering, measuring, and reporting medications


Metrication of the World

The only countries not using SI Metric System are USA, Liberia and Myanmar


Metric Prefixes

micro one millionth or 0.000001 or 11,000,000

of the base unit

milli one thousandth or 0.001 or 11,000

of the base unit

centi one hundredth or 0.01 or 1100

of the base unit

deci one tenth or 0.1 or 110

of the base unit

kilo one thousand or 1,000 times the base unit


International System (SI) of Metric Units and Abbreviations

• Weight Gram (base unit)-g

Milligram-mg

Microgram-mcg

Kilogram-kg


International System (SI) of Metric Units and Abbreviations• Volume

Liter (base unit)-L Milliliter-mL Cubic centimeter- cc *

* the cc abbreviation should

not be used as it can be mis-interpreted for zeroes if poorly written


International System (SI) of Metric Units and Abbreviations

• LengthMeter (base unit)-m

Centimeter-cm

Millimeter-mm


Comparing Common Metric Units

PREFIX

KILO- Hecto- Deka- BASE DECI- CENTI- MILLI- Decimilli-

Centimilli-

MICRO-

Weight kilogram gram milligram microgram

Volume liter deciliter Milliliter

Length meter centimeter Millimeter

Value to Base

1,000 100 10 1.0 0.1 0.01 0.001 0.0001

0.00001

0.000001


Rules of Metric Notation• Unit or abbreviation always follows amount

– 5 g NOT g 5

• Decimals are used to designate fractional metric units – 1.5 mL, NOT 1 mL

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Rules of Metric Notation• Use a zero to emphasize decimal point

for fractional metric units of less than 1 – 0.5 mg, NOT .5 mg– Will prevent potential dosage error – If you misinterpreted medication order as 5 mg

instead of 0.5 mg• Dosage would be 10 times too much


Rules of Metric Notation

• Omit unnecessary zeros– 1.5 g, NOT 1.50 g– This is a critical rule

• When in doubt, double-check – Ask writer for clarification


Most commonly usedMetric Measurements and Equivalents

Unit Abbreviation Equivalents

gram g 1 g = 1,000 mg

milligram mg 1 mg = 1,000 mcg

microgram mcg

Weight


Most Commonly Used Metric Measurements and Equivalents

Unit Abbreviation Equivalents

liter L 1 L = 1,000 mL

milliliter mL

Volume


The Apothecary System

•Originated in Greece

•First system of medication measurement

•One grain = weight of a single grain of wheat [60mg]

•One grain = 60 mg is the ONLY apothecary conversion you will need to memorize


Apothecary System of Measurement• Currently being phased out as a system of measurement, but

some units for dosage calculations that may still be seen are:– Grain (gr)– Ounce (oz)!Notice the similarity between the abbreviation for grain (gr) and gram (g). Be careful not to confuse them!

• Other units in apothecary system not in use but still on some syringes and medicine cups are: minims and drams

• Quantities are usually expressed in lowercase Roman numerals

• Amounts greater than ten may be expressed in Arabic numbers– Except 15 (xv), 20 (xx), and 30 (xxx)


Apothecary System of Measurement

• Quantities of less than one are expressed as fractions, except – One-half is expressed by the symbol ss

• Abbreviation or symbol is clearly written before quantity Example: gr 15 gr XV gr ½ gr ss

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Apothecary System of Measurement

• The apothecary system is NOT recommended for use by JCAHO.

• Ask the prescriber to re-write in metric or if you are unsure about the exact meaning of any medical notation– Do not guess or assume– Ask writer for clarification


Household System of Measurement

• Household measures are not accurate enough to be used in calculation of drug dosages.

• However, when sending patients home with liquid medications, it is sometimes necessary.

• Advise patients to use the measuring device provided with their prescription or an accurate measuring spoon [ not normal tableware]


Units uses inHousehold Measurement

• Drop (gtt)• Teaspoon (t)• Tablespoon (T)• Ounce (oz) • Cup (cup)• Pint (pt)• Quart (qt)• Pound (lb)


Other Types of Drug MeasurementsUnits

• Standardized amount needed to produce a desired effect

• Most commonly used for medications:Insulin, Heparin, Penicillin

• CANNOT be abbreviated as (U)(See JCAHO Do Not Use List)

• Must be written out as the word Units


Units


Milliequivalents (mEq)

• One thousandth of an equivalent weight of a chemical

• Most commonly used when referring to concentration of electrolytes


Milliequivalents (mEq)


Equivalents to MEMORIZE

1 grain (gr) = 60 milligrams (mg)1 teaspoon (t) = 5 milliliters (mL)

1 tablespoon (T) = 3 teaspoons (t)1 ounce (oz) = 30 milliliters (mL)

1 cup = 8 ounces (oz)1 Kilogram (Kg) = 2.2 pounds (lbs)

1 liter (L) = 1000 milliliters (mL)1 gram (g) = 1000 milligrams (mg)

1 milligram (mg) = 1000 micrograms (mcg)

copyright © 2008 thomson delmar learning systems of measurement metric / apothecary / household...

Documents

si metric system

fractional metric units

used metric measurements

myanmar slide

clarification slide

written slide

units of measurement

common metric units