Metric/International (SI) System Chapter 4 Metric/International (SI) System PNU 145, September. Cheryl Proffitt, RN,MSN

Metric System Système International (SI) Developed in France in 1875 Name stems from basic unit of measure Takes its name from Meter, length equivalent to yards

Metric/SI System Major strength of SI system is that ___ All units of measure differ from each other in powers of ten Conversions between units accomplished by simply moving the decimal point. NOTE: be careful when moving the decimal point it can alter the dosage if done incorrectly.

Examples of larger units/smaller Units of measure comparison in terms of smaller and larger units Pounds is larger than ounces.etc.

Basic Units of measure Length Meter Volume Liter Weight Gram

Terms with Prefixes Whether larger or smaller than basic units, all other units have name of basic unit incorporated in them E.g., kilogram, centimeter, milligram, microgram Same prefixes can be used with all three measures For example- kilometer, kilogram and kiloliter Prefixes can also units that are larger or smaller. Kilo is often used in clinical areas especially for weights

Terms with Prefixes 1 kilometer =1000 meters 1 kilogram =1000 grams 1 kiloliter = 1000 Liters 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 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 Gram (g) Milligram (mg) Microgram (mcg) Liter (L) Milliliter (mL) Kilogram (kg) Kilometer (km)

Why is Liter with L "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.

Notation Rules Units of measure are expressed in Quantity - written in Arabic numbers 1, 2, 3, 4, etc. E.g., 0.5 (mL) 1(mL), Numerals representing quantity placed before abbreviations E.g., 0.5 mL, 1mL ( not mL 0.5)

Notation Rules Full space used between number and abbreviation E.g., 0.5mL ( not 0.5mL) Fractional parts of unit are written in decimal fractions E.g., 0.5 mL ( not 1/2mL)

Notation Rules Zero placed in front of decimal point when not preceded by whole number Emphasizes decimal point E.g. 0.5mL (not .5mL) Excess zeros following decimal fraction eliminated E.g., 0.5mL ( not 0.50mL)

Common Weight Units Used in Health Care From Greater to Lesser values kg = kilogram g = gram mg = Milligram mcg = Microgram

Common Volume Units Used in Health Care Units of volume frequently used are . From greater to lesser values L = Liter & mL = milliliter

Conversion continues. Each of the clinical metric measures differs from the next by 1000. For example from greater to larger. 1kg = 1000 g 1g = 1000 mg 1mg = 1000 mcg 1L = 1000 mL. Recap: Values from greater to lesser for weights are as follows kg, g, mg, mcg. Differ by 1000

Metric Conversions Metric system is decimal system, so conversion between units are accomplished by moving the decimal point 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

Conversions Which way do you move decimal point Values from greater to lesser for weights are as follows kg- g- mg- mcg. 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 For example: 0.5g to mg Move decimal point 3 places to the right 0.5= 0.500 Eliminate the 0 at the front So now we have a larger unit of 500mg Even though you are converting to a smaller unit, the quantity will be larger.

Conversions 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. For example 200mL to L 200 ml to L= 200 move 3 places to Left .200 .= Eliminate 2 zeros at end, and add 0 before the point= 0.2L

Conversions tips Large to small –3places to right Small to large – 3 places to left

References Curran, A.Witt, M. (2014) Math for Meds, dosage and solutions. ( 11th ed) . Cengage learning, Stamford, CT.