Download Calculations in Health Care

Calculations in Health Care
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AIM
– To introduce the S.I units used in the field
of nursing and medicine
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Learning outcomes
– aware of some of the different units of
measurements
– aware of numeric skills required by the
nurse
Calculations in Health Care
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Fundamental SI units
Physical Quantity
Name
Length
metre
Mass
kilogram
Time
second
Current
ampere
Temperature
Kelvin
Amount of substance
mole
mol Luminous intensity candela
cd
Symbol
Kg
s
K
m
A
Calculations in Health Care
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Common derived units:
Quantity
Name
Force
newton
N
Energy
joule
Pressure
pascal
Potential difference volt
V
Frequency
hertz
Volume
litre
Symbol
J
Pa
Hz
L
Calculations in Health Care
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Names and abbreviations of SI unit multiples and sub
multiples:
Prefix Symbol
mega
M
kilo
k
hecto
h
deca
da
deci
d
centi
c
milli
m
micro μ
Meaning
one
one
one
ten
one
one
one
one
Scientific notion
million
thousand
hundredth
tenth
hundredth
thousandth
millionth
10 (6)
10(3)
10(2)
10(1)
10(-1)
10(-2)
10(-3)
10(-6)
Important S.I. units
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Kilogram
– the gram is often used as the base unit in hospitals.
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Litre
– is used as the base unit for volume
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Kelvin
– not used that much in nursing, rather it is the celsius
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Metre
Second
Joules
– used by dieticians to measure energy from foods
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Millimoles
– used to measure concentration of substances in fluids
Important non-SI units
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Celsius
– this is used extensively with most equipment measuring
body temperature. Some may refer to the Farenheit
scale. There is a conversion formula available to turn
value in to celsius
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Column of mercury (mm Hg)
– used extensively in measuring blood pressure with
mercury and aneroid sphyghnometers
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Milliequivalent
– used to measure concentration of fluids
Weight and Mass
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Mass
– this is the quantity of matter that a substance contains
when compared with a standard piece of SI platinum. This
standard has a mass defined in Kg.
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Weight
– this is the relative heaviness of a substance, usually
expressed in kilograms
Pressure
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Pascal
– this is the SI unit of pressure. It is commonly used
as unit in blood gas estimations.
– Blood pressure measurements continue to be
measured in mmHg
mm Hg X 0.133 = Pascal
– companies producing pressure relieving
mattresses use mm Hg as a measure of pressure
in their brochures
Energy
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Joule
– this is the potential energy which is
released when 1Kg weight falls through 1
metre by force of gravity.
– Joule is to replace the calorie as the unit of
energy.
– The joule is smaller than the dietary
calorie, hence dieticians use Kilojoule
Calorie X 4.184 = Kilojoule
Concentration of substances
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Mole
– this is the amount of substance present in a given
volume of one litre.
– body function relies upon a balanced
concentration of many different substances. They
form the basis for biochemical tests
– within a population, a normal concentration of
particular substances have been determined for
many body chemicals.
Concentration of substances
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Milliequivalent
– A milliequivalent is determined by relating
the ability of an element to combine with,
or displace, hydrogen.
– 1 milliequivalent of one substance does not
necessarily contain the same number of
particles as 1 milliequivalent of another
substance.
Concentration of substances
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Weight-volume
– prior to the introduction of SI units,
substances were sometimes expressed as
number of grams per 100 ml of water
– this is the same as percentage solution,
such as 5% dextrose IV fluids
Calculation skills required of the nurse
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Addition and subtraction
Multiplication and division (able to use conversion
factors)
Percentages, ratios, proportions
Deal with fractions
Deal with decimal points
Able to convert one system of units into another
(imperial units into metric units for weight, length)
Able to convert metric units
Able to use formulae and equations
Able to use and interpret charts (nomogram, growth,
BMI)
Moving and Handling
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Specific weight assessment
– Weight of a patient is usually in Grams or Kilograms,
although many people still relate to the Imperial
measurement of stones and pounds. You will need to know
the conversion factor, and hence be able to have the
arithmetical skill of multiplication:
– conversion factor if 1Kg =2.2 imperial pounds
14pounds =1stone
– Moving and Handling regulations provide guidelines on
safe working loads you should handle.
Moving and Handling
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Lifting loads in standing position (max weight 15 Kg for men)
Lifting loads in a sitting position (for women 3 Kg)
Pushing or pulling loads (starting force for women 16Kg or160
Newtons)
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When pushing or pulling clients on beds, wheelchairs or loads,
you will need to understand biomechanics, i.e force, vector
analysis, centre of gravity, base, friction
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Knowledge of biomechanics are useful in orthopaedics,
physiotherapy, moving and handling, pressure damage
prevention
Moving and Handling
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Specific patient risk assessment may require you to
calculate the Body Mass Index
Height/ weight = numeric score
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Certain score ranges indicate whether the person is
obese, normal weight or underweight
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Height measurements are usually in metres but some
patients still think in imperial units of feet and inches,
you may have to convert into metres.
Drug Administration
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Tablets
– these may come in dosages of micrograms, milligrams or grams
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Capsules
– these may again come in dosages such as above
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Elixirs, syrups, Emulsions, Linctus
– usually measured in mg/ml or microgram/ml
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Injections
– usually measured as mg/ml or microgram/ml (also measured in units)
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Inhalers
– measured as micrograms/ puff
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Topical medication
– these may be measured as %/ ml as in eye drops, or mg, micrograms
per patch
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Fluids
– these are usually prescribed as weight-volume, although milliequivalents
Drug Administration
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Household measures
– these are used when calibrated devices are not
available. Household utensils are used in the home
setting.
– 1 teaspoon = 4-5 ml
– 1 tablespoon = 15 ml
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Apothercaries’ system
– this has been largely replaced by the metric
system but is still used occasionally (e.g fluid
ounces)
Paediatric Drug Calculations
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The dosage of many drugs is smaller than of the same drug for an adult.
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Calculations are based on the amount of the drug per kilogram of body
weight or on body surface
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Estimating body surface area can be done using the West Nomogram
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Clark’s formula can be used to determine whether the prescribed dose
seems reasonable based upon the weight of the child
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Young’s formula, based on the age of the child, can give you the child’s
equivalent dosage to an adult dosage for a drug
Infection Control
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Antiseptics
– expressed as % w/v e.g 1% w/v iodine in aquous
solution
Disinfectants
– this may be expressed in grams tablets that require
dissolving in water. For x 7 ActiChloride 2.5g tablets,
there will be 10,000 parts per million chlorine
available when dissolved in 1 litre of water
– spray disinfectants may be expressed as % w/v
e.g Dispray chlorhexadine gluconate 0.02% w/v
( 0.2mls of chlorahexadine gluconate is diluted in 1
litre of water)
Biochemical Results
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A knowledge of volume, weight, length, time, amount
of substance, osmolality is required:
Arterial Blood gases
– PaCO2
35-45 mmHg
– PaO2
>80 mmHg
Chloride is measured as mEq/L
cholestrol is measured as mg/dL
serum cortisol as
µg/dL
urine cortisol as
µg/24 hr
serum osmolality as
mOsm/kg
urine osmolality as
mOsm/L
Haemotology Results
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A knowledge of volume, weight, length, time and
percentage is required.
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Red Blood Cells (RBC) is measured as X 10 (-6) /cubic
mm
Haemoglobin (Hb) is measured as g/dl
Platelet count is measured in % or parts per 100
Sedimentation Rate is measured in mm/hr
MCV is measured in microgram/ cubic metre or ų-3m
There are many more constituents to blood but all
use the above units of measurements
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Public Health Results
Nutritional Assessment
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The following units of measurement will be important
for the dietician:
– anthropemetric measurements (height, weight,
skinfold thickness and muscle mass)
–
–
–
–
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weight of the client in Kg
height of the client in order to determine the BMI
volume of fluids intake/output measured in L
energy in joules or calories given by food
constituent of food, such as carbohydrates,
proteins, fat, minerals and vitamins
– food constituents are measured in g, mg or µg
Growth and Development
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Percentile charts are statistical charts indicating
normal distribution of weight and height for age
categories of children’s growth within a given
population.
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Hence you will have to become familiar with the
concept of percentiles in statistics, and measuring
weight and height of children (Kg and cm)
Blood Pressure
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Although the S.I unit is the Pascal, with traditional
mercury sphygnometers the measurement is in
mmHg.
Invasive monitoring of blood pressure may be
measured in pascals
You will rarely have to convert one unit of
measurement into another but you will need to be
aware of what normal limits are for the client of a
given age if readings are in pascal, as well as mm of
mercury (Hg)
Pulse
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This is usually measured as the number of pulsatile
beats per minute e.g 60 beats for every second
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The pulse should be measured over a full second to
obtain an accurate number of beats
Respiration and ventilation
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Respiration is measured over a full minute or 60 seconds by the
nurse.
Other observational factors are considered, such as the
breathing pattern, noise of inhalation etc.
Ventilation of patients occur in critical care settings with
respirators.
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There are negative and positive respirators according to
whether they are helping with inhalation or exhalation.
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Pressure > than standard atmospheric pressure (101kPa or
760mmHg) is often referred to as positive pressure,and those <
than standard atmospheric pressure is referred to as negative
Body Temperature
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Body temperature is usually measured in Celsius
The Farenheit scale of 32 to 212 F encompasses the same
temperature range as 0 to 100 Celsius scale.
– Conversion of Farenheit into celsius:
C=
5 (F-32)
e.g 37C =
5 (98-32) =5(66)=36.6
9
9
9
– Conversion of Celsius into Farenhet is done by:
F=
9 (C) + 32
5
Relevance of measurements to some
nursing intervention sessions
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Infection Control
– concentration of chemicals for antiseptics, disinfectants
Hygiene
– concentration of chemicals in mouth washes, toothpaste, creams
Handwashing
– chemical concentration in soaps, alcohol rubs
Oxygenation
– blood gases, oxygen saturations, flow rates of oxygen, peak flow
measurements
Eating and drinking
– energy value of food, flow rates of feeds, fluid balance charts
Elimination
– urinary output, catheter balloons
Skin integrity
– pressure of blood capillary occlusion, pressure relieving products
Conclusion
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The most important area for numeracy skills is in drug administration
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Understanding some scientific concepts will help you understand why some
interventions are undertaken in a particular way e.g moving and handling
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In the areas of paediatrics, neonatal care, intensive and critical care,
accurate drug calculations are required for drug administration
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High standards of drug administration is required at all times
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An understanding of other S.I units, such as millimoles, will enable you to
understand the consequences of your nursing intervention
REFERENCES
J.D.Gatford and R.E.Anderson (1998) Nursing Calculations (5th
edition); Churchill Livingston:London
Nancy D. Dienpenbrock (2000) Quick Refence to Critical Care;
Lippincott:USA
Norma Dison (1992) Simplified Drugs and Solutions for Nurses
including mathematics (10th edition);Mosby: USA
Hinwood, B. (1992) A textbook of science for the health
professions (2nd edition); Chapman & Hall:London
Brown Mulholland (19 ) Drug Calculations Process and
problems for clinical practice (4th edition); Mosby:USA
M.F.Alexander,J.N.Fawcett and P.J.Runciman (19 ) Nursing
Practice Hospital and Home The Adult; Churchill Livingstone:
London