Copyright © 2008 Thomson Delmar Learning Systems of Measurement Metric / Apothecary / Household...
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Transcript of 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
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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
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Metrication of the World
The only countries not using SI Metric System are USA, Liberia and Myanmar
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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
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International System (SI) of Metric Units and Abbreviations
• Weight Gram (base unit)-g
Milligram-mg
Microgram-mcg
Kilogram-kg
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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
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International System (SI) of Metric Units and Abbreviations
• LengthMeter (base unit)-m
Centimeter-cm
Millimeter-mm
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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
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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
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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
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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
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Most Commonly Used Metric Measurements and Equivalents
Unit Abbreviation Equivalents
liter L 1 L = 1,000 mL
milliliter mL
Volume
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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
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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)
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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
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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]
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Units uses inHousehold Measurement
• Drop (gtt)• Teaspoon (t)• Tablespoon (T)• Ounce (oz) • Cup (cup)• Pint (pt)• Quart (qt)• Pound (lb)
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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
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Milliequivalents (mEq)
• One thousandth of an equivalent weight of a chemical
• Most commonly used when referring to concentration of electrolytes
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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)