Chapter 4Metric/International (SI) System

PNU 145, September.

Cheryl Proffitt, RN,MSN

Metric SystemSystème International (SI)

O Developed in France in 1875O Name stems from basic unit of measure

O Takes its name from Meter, length equivalent to yards

Metric/SI System

O Major strength of SI system is that ___

O All units of measure differ from each other in powers of tenO Conversions between units accomplished by simply

moving the decimal point.O NOTE: be careful when moving the decimal point it can

alter the dosage if done incorrectly.

Examples of larger units/smaller

O Units of measure comparison in terms of smaller and larger units

O Pounds is larger than ounces.etc.

Basic Units of measure

O LengthO Meter

O VolumeO Liter

O WeightO Gram

Terms with Prefixes

O Whether larger or smaller than basic units, all other units have name of basic unit incorporated in themO E.g., kilogram, centimeter, milligram, microgram

O Same prefixes can be used with all three measuresO For example- kilometer, kilogram and kiloliterO Prefixes can also units that are larger or smaller.O Kilo is often used in clinical areas especially for weights

Terms with Prefixes

O 1 kilometer =1000 metersO 1 kilogram =1000 gramsO 1 kiloliter = 1000 LitersO Some other units used in clinical areas are Milli – milligram- weight Micro-microgram- weight Centi- centimeter- Length Putting it all together the four basic units in clinical areas

–Kilo, centi, micro,milli.

Abbreviations

O How to abbreviate-the basic units are abbreviated to their first initials and printed in small lower case letters. Exception is Liter with upper case L

O Gram (g)O Milligram (mg)O Microgram (mcg)O Liter (L)O Milliliter (mL)O Kilogram (kg)O Kilometer (km)

Why is Liter with LO

"L" is the symbol for liter, not abbreviation the use of capital has suggested from National Institute of Standards and Technology because "l" looks like numb 1, so L is safer and is recommended.

O

Notation Rules1. Units of measure are expressed in

2. Quantity - written in Arabic numbersO 1, 2, 3, 4, etc.O E.g., 0.5 (mL) 1(mL),

3. Numerals representing quantity placed before abbreviations

O E.g., 0.5 mL, 1mL ( not mL 0.5)

Notation Rules

3. Full space used between number and abbreviation

O E.g., 0.5mL ( not 0.5mL)

4. Fractional parts of unit are written in decimal fractions

O E.g., 0.5 mL ( not 1/2mL)

Notation Rules

5. Zero placed in front of decimal point when not preceded by whole number

O Emphasizes decimal pointO E.g. 0.5mL (not .5mL)

O Excess zeros following decimal fraction eliminated

O E.g., 0.5mL ( not 0.50mL)

Common Weight Units Used in Health Care

O From Greater to Lesser values

O kg = kilogramO g = gramO mg = MilligramO mcg = Microgram

Common Volume Units Used in Health Care

O Units of volume frequently used are . From greater to lesser values

O L = Liter &O mL = milliliter

Conversion continues.

O Each of the clinical metric measures differs from the next by 1000. For example from greater to larger.

O 1kg = 1000 gO 1g = 1000 mgO 1mg = 1000 mcgO 1L = 1000 mL.O Recap: Values from greater to lesser for weights are as

follows kg, g, mg, mcg. O Differ by 1000

Metric ConversionsO Metric system is decimal system, so conversion between

units are accomplished by moving the decimal point O The decimal is moved according to difference in value,

for example if difference in value is − 10- which has one 0, move decimal one place.− 100- which has two 0, move decimal two places− 1000- which has three 0, move decimal three places

ConversionsO Which way do you move decimal pointO Values from greater to lesser for weights are as

follows kg- g- mg- mcg.

O When converting to a smaller units of measure , for example g to mg. ( g is larger and mg is smaller unit).We know that the decimal point is moved 3 places to the right

Conversions

O For example: O 0.5g to mgO Move decimal point 3 places to the rightO 0.5= 0.500O Eliminate the 0 at the frontO So now we have a larger unit of 500mgO Even though you are converting to a smaller unit, the

quantity will be larger.

Conversions

O If you are converting from a smaller to larger unit of measurement such as mL to L, move decimal point three places to the left.

O For example 200mL to LO 200 ml to L= 200 move 3 places to LeftO .200 .= O Eliminate 2 zeros at end, and add 0 before the

point= 0.2L

Conversions tips

O Large to small –3places to right

O Small to large – 3 places to left

ReferencesO Curran, A.Witt, M. (2014) Math for Meds, dosage and

solutions. ( 11th ed) . Cengage learning, Stamford, CT.