Chapter 03 Revised 2.2018.ppt - Los Angeles Harbor College

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Chapter 3

Systems of Measurement



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

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Metric System

3 Base Units

1. Weight

2. Volume

3. Length


Metric System

WEIGHT

• Most utilized parameter

• Important as a dosage unit

• The metric base unit of weight is the gram (g)


Metric SystemVOLUME

• 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

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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)


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!!


Metric Prefixes

1micro = one millionth or 0.000001 or of base unit1,000,000

1milli = one thousandth or 0.001 or of base unit1,0001centi = one hundredth or 0.01 or of base unit

1001deci = one tenth or 0.1 or of base unit

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kilo = one thousand or 1,000 times base unit

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International System (SI) of Metric Units and Abbreviations

• Weight– gram (g)

• Base unit

– milligram (mg)

– microgram (mcg)

– kilogram (kg)


SI of Metric Units and Abbreviations

• Volume– liter (L) as the base unit

– deciliter (dL)

– milliliter (mL)


SI of Metric Units and Abbreviations

• Length– meter (m) as the base unit

– centimeter (cm)

– millimeter (mm)

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Comparing Common Metric Units

Prefixkilo- hecto- deca- 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


• 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).


Remembering Order

gram

liter

meter

kilo hecto deca BASE deci centi milli

K H D D C M

“King Henry Died from a Disease Called Mumps”

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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



• Avoid adding “s” to make unit plural– E.g., 7 mL (not 7 mLs)

– Could be mistaken for another unit



• 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)

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• 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



• Use decimals to designate fractional metric units– E.g., 1.5 mL (not 1 mL)

• Omit unnecessary (trailing) zeros– E.g., 1.5 g (not 1.50 g)

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• Avoid using abbreviation µg for microgram– Could be mistaken for mg

• 1,000 times larger

– Acceptable abbreviation:• mcg

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• 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 youare not sure of the abbreviation or notation used. Never guess!


Metric Base UnitsThe 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


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

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Metric Measurements and Equivalents: Volume


liter L 1 L = 1,000 mL

milliliter mL 1 mL = 0.001 L


Metric Measurements and Equivalents: Length


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


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!!

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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


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?....


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

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Household System of Measurement


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


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


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

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Units

• Milliunit is one thousandth ( ) of a unit– Some drugs measured in milliunits

• E.g., oxytocin

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1,000


Milliequivalents (mEq)

• One thousandth ( ) 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”

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1,000


Chapter 03 Revised 2.2018.ppt - Los Angeles Harbor College

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