1. Metric/International (SI) System
Chapter 4
Metric/International (SI) System

2. Metric System/Système International (SI)
Developed in France in 1875
Name stems from basic unit of measure
Meter

3. Metric/SI System Advantage
All units of measure differ from each other in powers of ten
Conversions between units accomplished by simply moving decimal point

4. Metric/SI System Disadvantage
In drug dosages, greatest hazard is that misplaced decimal point alters dosage by multiple of at least 10

5. Basic Units
Length
Meter
Volume
Liter
Weight
Gram

6. Terms
Whether larger or smaller than basic units, all other units have name of basic unit incorporated in them
e.g., kilogram, centimeter, milligram, microgram

7. Prefixes
Identical prefixes used with all basic metric measurements to identify larger or smaller units:
kilo
milli
micro
centi

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

9. Notation Rules Quantity written in Arabic numbers
1, 2, 3, 4, etc.
e.g., 5 mL, 125 mcg, 11 cm, 62 kg, 35 mg
Numbers representing quantity placed before abbreviations
e.g., 3 mL, 10 kg, 6 mg, 250 mcg, 8 cm

10. Notation Rules Full space used between number and abbreviation
e.g., 10 mg, 100 L, 15 mcg
Fractional parts of unit written in decimal fractions
e.g., 34.5 mg, 2.5 mL, 78.2 kg

11. Notation Rules
Zero placed in front of decimal point when not preceded by whole number
Emphasizes decimal point
e.g., 0.25 mg, 0.5 g
Excess zeros following decimal fraction deleted
e.g., g = 4.5 g, L = 2.5 L

12. Common Weight Units Used in Health Carekg g mg
mcg

13. Common Volume Units Used in Health CaremL

14. Conversions
Move decimal point three places when units of clinical measure differ by 1000
Move the same as the number of zeros

15. Conversions
When converting from smaller to larger units in same basic unit of measure, move decimal point three places to the left
e.g., weight
Numerical answer will be smaller

16. Conversions
When converting from larger to smaller units in same basic unit of measure, move decimal point three places to the right

17. Errors
Most occur because prescriptions not properly notated or inaccurately transcribed
Usually involve decimal fractions

18. Avoiding Errors Use reasoning powers
Question quantities that seem unreasonable