Transcript Clinical calculations

Clinical calculations
Dimensional analysis
= label factor method = unit-conversion
method
• Computation method whereby one
particular unit of measurement is
converted to another unit of
measurement by use of a conversion
factor or factors
Answer unit
Starting factor
Conversion
factors
Steps in Dimensional Analysis
1. Determining the starting factor and
answer unit
2. Formulating a conversion equation
3. Solving the convertion equation
Step I: Determining the Starting
Factor and Answer Unit
Example:
How many inches are there in 29 feet?
• 29 feet – known quantity, which have
to be converted – starting factor
•
The desired unit – answer unit (in)
Step II: Formulating the
Conversion Equation
• Conversion factors – bridges leading
from starting factor to the desired
unit
• The numerator and denominator must
be of equivalent value
• The fraction always is equal to 1
Step II: Formulating the
Conversion Equation
• 1 hr = 60 min – equivalents
• 1 hr/60 min = 60 min/1 hr - conversion
factors
Step II: Formulating the
Conversion Equation
Example: Find the number of minutes in
90 seconds
Equivalents: 1 min=60 sec
Conversion Equation:
Starting
factor
Convertion
factor
Answer
unit
90 sec × 1 min/60 sec = ___ min
Solving the conversion
equation
Example: Find the number of yards in 1.5 miles
• Equivalents: 1 mi = 5280 ft; 3 ft = 1 yd
• Equation:
1.5 mi × 5280ft/1 mi × 1yd/3ft
The identical units must be placed
diagonally (in the numerator of one factor
and in the denominator of the factor
immediately following)
Solving the conversion
equation
• 1.5 mi × 5280ft/1 mi × 1yd/3ft
1.5 × 5280/1 × 1 yd/3
(1.5 × 5280)/3=2640 yd
Systems of Measurement
• The metric system
• The apothecaries’ system
• The household system
Metric System of
Measurement
• Based on the decimal system
• Basic units:
– Gram – for weight
– Liter – for volume
– Meter – for length
Metric Units and
Abbreviations
Weight
Gram
Miligram
Microgram
Kilogram
g
mg
mcg (μg)
kg
Volume
Liter
Milliliter
Length
Meter
Centimeter
Millimeter
m
cm
mm
L
mL (cc)
Apothecaries’ System of
Measurement
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The measures are approximations
Roman numerals are often used
Fractions are used (ss = ½)
Symbol for a unit of measure is written
before the quantity – gr viiss = gr VIIss
A combination of Arabic numerals
and fractions can be used - gr 7 ½
Apothecaries’ System of
Measurement
• Weight
– The basic unit is grain (gr)
gr 15 = 1 g 60 mg = gr 1
– Dram (medication cup) dr
– Ounce – oz
– Pound (lb) = 16 oz
Apothecaries’ System of
Measurement
• Volume
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The smallest unit is the minim (m)
Dram (dr) dr 1= 4 mL
Ounce (oz) = 30 mL
Pint (pt) pt 1 =oz 16 = 500 mL
Quart (qt) qt 1 = pt 2= 1,000 mL
Household System
• Some of the units for liquid measures are
the same as those in the apothecaries’
(pint and quart)
• There are no standart rules for expressing
household measures
• Standart cookbook abbreviations, Arabic
numerals and fractions are used
Household Units
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Drop (gtt)
Teaspoon (t, tsp)
Tablespoon (T, tbs) 1 tbs = 3 tsp
Cup (C) 1 C = 16 tbs
Pint (pt) 1 pt = 2 C
Quart (qt) 1 qt = 2 pt
1 glassful = 8 ounces
Apothecaries’/Household/
Metric Equivalents
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1 ounce (oz) = 30 mL
1 dram (dr) = 4 mL
1 tablespoon (T or tbs) = 15 mL
1 teaspoon (t or tsp) = 5 mL
1 cup = 240 mL (8 ounces)
1 pint (pt) = 500 mL (16 ounces)
1 quart (qt) = 1,000 mL (32 ounces)
15 or 16 minims (m) = 1 mL
1 kg = 2.2 lb