Chapter 3 Systems of Measurement Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric System • Preferred system of measurement in healthcare • Universal and international, • Used for prescribing, measuring and recording medications because, as a decimal system, it is precise • Based on the powers of 10 with 3 Base Units Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 1 Metric System 3 Base Units 1. Weight 2. Volume 3. Length Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric System WEIGHT • Most utilized parameter • Important as a dosage unit • The metric base unit of weight is the gram (g) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric System VOLUME •2nd most used parameter • Usually refers to liquids • Think “capacity” how much a container holds • Additionally, uses Quantity & Concentration (amount and strength of a solution) • The metric base unit of length is liter (L) • millileter (mL) most common volume unit Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 2 Metric System LENGTH • Least utilized parameter • Linear measurement used in health care (height, amount of ointment ,size of laceration) • The metric base unit is meter (m) • Most length measurements are in millimeter (mm) or centimeters (cm) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric System In the Metric System, Pre-fixes aka “sub-units” are used to show which portion of the base unit is being considered. NEED to know most commonly used pre-fixes or “sub-units” for health care!! Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric Prefixes micro = one millionth or 0.000001 or 1 of base unit 1,000,000 milli = one thousandth or 0.001 or 1 of base unit 1,000 centi = one hundredth or 0.01 or 1 of base unit 100 deci = one tenth or 0.1 or 1 of base unit 10 kilo = one thousand or 1,000 times base unit Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 3 International System (SI) of Metric Units and Abbreviations • Weight – gram (g) • Base unit – milligram (mg) – microgram (mcg) – kilogram (kg) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. SI of Metric Units and Abbreviations • Volume – liter (L) as the base unit – deciliter (dL) – milliliter (mL) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. SI of Metric Units and Abbreviations • Length – meter (m) as the base unit – centimeter (cm) – millimeter (mm) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 4 Comparing Common Metric Units Prefix kilo- hecto- deca- base deci- centi- milli- decimilli- centimilli- micro- Weight kilogram gram milligram microgram Volume liter deciliter milliliter Length meter centimeter millimeter Value to 1,000 100 10 1.0 0.1 0.01 0.001 0.0001 0.00001 0.000001 Base Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. • Units in the metric system are all related by a power of 10, which means that each successive unit is 10 times larger than the previous one. This makes converting one metric measurement to another a straightforward process, and is often as simple as moving a decimal point. It is always important, though, to consider the direction of the conversion. If you are converting a smaller unit to a larger unit, then the decimal point has to move to the left (making your number smaller); if you are converting a larger unit to a smaller unit, then the decimal point has to move to the right (making your number larger). Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Remembering Order gram liter meter kilo hecto deca BASE deci centi milli KHD DCM “King Henry Died from a Disease Called Mumps” Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 5 Rules of Metric Notation • Always put unit or abbreviation after amount – E.g., 5 g (not g 5) • Avoid putting period after unit abbreviation – E.g., mg (not mg.) – Could be mistaken for number one Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Rules of Metric Notation • Avoid adding “s” to make unit plural – E.g., 7 mL (not 7 mLs) – Could be mistaken for another unit Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Rules of Metric Notation • Separate amount from unit – E.g., 20 mg (not 20mg) – Otherwise number and unit run together • Unit could be mistaken as zero • Place commas for amounts of 1,000 or more – E.g., 10,000 mcg (not 10000 mcg) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 6 Rules of Metric Notation • Use leading zero to emphasize decimal point for fractional metric units of less than one – E.g., 0.5 mg (not .5 mg) – Prevents potential dosage error • Misinterpreted medication order as 5 mg rather than 0.5 mg would be 10 times appropriate dosage Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Rules of Metric Notation • Use decimals to designate fractional metric units 1 – E.g., 1.5 mL (not 1 mL) 2 • Omit unnecessary (trailing) zeros – E.g., 1.5 g (not 1.50 g) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Rules of Metric Notation • Avoid using abbreviation µg for microgram – Could be mistaken for mg • 1,000 times larger – Acceptable abbreviation: •mcg Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 7 Rules of Metric Notation • Avoid using abbreviation cc for mL – Could be mistaken for zeros • When in doubt, double-check – Ask writer for clarification If in doubt, always ask the writer to clarify if you are not sure of the abbreviation or notation used. Never guess! Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric Base Units The only units that may stand alone in the metric system are: m = meter L = liter g = gram Some people mistake m for milli but milli has to precede one of these base units (mL, mg, or mm) - milli cannot stand alone as m Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric Measurements and Equivalents: Weight Unit Abbreviation Equivalents gram g 1 g = 1,000 mg milligram mg 1 mg = 1,000 mcg = 0.001 g microgram mcg 1 mcg = 0.001 mg = 0.000001 g kilogram kg 1 kg = 1,000 g Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 8 Metric Measurements and Equivalents: Volume Unit Abbreviation Equivalents liter L 1 L = 1,000 mL milliliter mL 1 mL = 0.001 L Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Metric Measurements and Equivalents: Length Unit Abbreviation Equivalents meter m 1 m = 100 cm = 1,000 mm centimeter cm 1 cm = 0.01 m = 10 mm millimeter mm 1 mm = 0.001 m = 0.1 cm Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. QUICK REVIEW • The metric base units are gram (g), liter (L), and meter (m). • Sub-units are designated by appropriate pre-fix and base unit such as milligram (mg) • There are 10 critical rules for ensuring amounts and units are accurate. LEARN THEM! • NEVER GUESS the meaning of a metric notation. ASK!! Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 9 APOTHECARY AND HOUSEHOLD SYSTEMS • First system of medication measurement used by apothecaries (aka pharmacists/MD’s) • Originated in Greece • Prevalent in home care settings, disappeared from hospitals and health care in the 1950’s • Pints, quarts, gallons • Grain, ounce, pound Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. APOTHECARY AND HOUSEHOLD SYSTEMS • The Institute for Safe Medication Practices (2013) discouraged use • Customary to express in Roman numerals • Remnants remain…aspirin grains 5 still found on some disposable medicine cups with its metric counterpart 325 mg, drams and ounces • Considered obsolete WHAT DO YOU DO IF?.... Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. HOUSEHOLD SYSTEM • Used by patients at home • Important for Medication Reconciliation • Important for Discharge Teaching • Important for advising patients/families about take home medications • Tele-nursing • Use of fractional amounts expressed as common fractions Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 10 Household System of Measurement Unit Abbreviation Equivalents drop gtt teaspoon t (or tsp) 3 t = 1 T tablespoon T (or tbs) 1 T = 3 t ounce (fluid) fl oz 2 T = 1 fl oz ounce (weight) oz 1 pound (lb) = 16 oz cup cup 1 cup = 8 fl oz pint pt 1 pt = 2 cups = 16 fl oz quart qt 1 qt = 4 cups = 2 pt Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Approximate Equivalents • 1 t = 5 mL • 1 T = 3 t = 15 mL = ½ fl oz • 1 fl oz = 30 mL = 6 t = 2 T • 1 L = 1 qt = 32 fl oz = 2 pt = 4 cups • 1 pt = 500 mL = 16 fl oz = 2 cups • 1 cup = 250 mL = 8 fl oz • 1 kg = 2.2 lb • 1 inches (in) = 2.5 cm Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Units • Standardized amount needed to produce desired effect – Used to measure unit of potency • Vitamins • Chemicals • Heparin • Insulin • No abbreviation – Write “unit” or “international unit” – No conversion as ordered dosage & supply dosage are in the same system Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 11 Units 1 • Milliunit is one thousandth ()1, 000 of a unit – Some drugs measured in milliunits • E.g., oxytocin Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Milliequivalents (mEq) 1 • One thousandth ()1,000 of equivalent weight of chemical – Used when referring to concentration of serum electrolytes such as calcium, magnesium, potassium and sodium – The abbreviations U and IU included on the “Do Not Use List” Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED. 12.