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Calculations in Health Calculations in Health CareCare
AIMAIM– To introduce the S.I units used in the field To introduce the S.I units used in the field
of nursing and medicineof nursing and medicine
Learning outcomesLearning outcomes– aware of some of the different units of aware of some of the different units of
measurementsmeasurements– aware of numeric skills required by the aware of numeric skills required by the
nurse nurse
Calculations in Health Calculations in Health CareCare
Fundamental SI unitsFundamental SI unitsPhysical QuantityPhysical Quantity NameName
SymbolSymbol LengthLength metremetremm MassMass
kilogramkilogram KgKg TimeTimesecondsecond ss CurrentCurrent
ampereampere AA TemperatureTemperatureKelvinKelvin KK
Amount of substanceAmount of substance molemole molmolLuminous intensityLuminous intensity candelacandelacdcd
Calculations in Health Calculations in Health CareCare
Common derived units:Common derived units:
QuantityQuantity NameNameSymbolSymbol ForceForce newtonnewtonNN EnergyEnergy joulejoule
JJ PressurePressurepascalpascal PaPa Potential Potential
differencedifference voltvolt VV FrequencyFrequencyhertzhertz HzHz
VolumeVolume litrelitre LL
Calculations in Health Calculations in Health CareCare
Names and abbreviations of SI unit multiples and Names and abbreviations of SI unit multiples and sub multiples:sub multiples:
PrefixPrefix SymbolSymbol MeaningMeaning Scientific notion Scientific notion megamega MM one millionone million 10 (6)10 (6) kilokilo kk one thousandone thousand 10(3) 10(3) hectohecto hh one hundredthone hundredth 10(2)10(2) deca deca da da tenten 10(1)10(1) deci deci dd
one tenthone tenth 10(-1) centi 10(-1) centi ccone hundredthone hundredth 10(-2)10(-2) milli millimm one thousandthone thousandth 10(-3)10(-3)
micromicro μμ one millionthone millionth 10(-6)10(-6)
Important S.I. unitsImportant S.I. units KilogramKilogram
– the gram is often used as the base unit in hospitalsthe gram is often used as the base unit in hospitals.. Litre Litre
– is used as the base unit for volumeis used as the base unit for volume KelvinKelvin
– not used that much in nursing, rather it is the celsiusnot used that much in nursing, rather it is the celsius MetreMetre SecondSecond JoulesJoules
– used by dieticians to measure energy from foodsused by dieticians to measure energy from foods MillimolesMillimoles
– used to measure concentration of substances in fluidsused to measure concentration of substances in fluids
Important non-SI unitsImportant non-SI units CelsiusCelsius
– this is used extensively with most equipment this is used extensively with most equipment measuring body temperature. Some may refer to measuring body temperature. Some may refer to the Farenheit scale. There is a conversion formula the Farenheit scale. There is a conversion formula available to turn value in to celsiusavailable to turn value in to celsius
Column of mercury (mm Hg)Column of mercury (mm Hg)– used extensively in measuring blood pressure used extensively in measuring blood pressure
with mercury and aneroid sphyghnometerswith mercury and aneroid sphyghnometers
MilliequivalentMilliequivalent– used to measure concentration of fluidsused to measure concentration of fluids
Weight and MassWeight and Mass
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.
Weight– this is the relative heaviness of a substance, usually
expressed in kilograms
PressurePressure
PascalPascal– this is the SI unit of pressure. It is commonly this is the SI unit of pressure. It is commonly
used as unit in blood gas estimations.used as unit in blood gas estimations.– Blood pressure measurements continue to Blood pressure measurements continue to
be measured in mmHg be measured in mmHg
mm Hg X 0.133 = Pascalmm Hg X 0.133 = Pascal– companies producing pressure relieving companies producing pressure relieving
mattresses use mm Hg as a measure of mattresses use mm Hg as a measure of pressure in their brochurespressure in their brochures
EnergyEnergy
JouleJoule– this is the potential energy which is this is the potential energy which is
released when 1Kg weight falls through 1 released when 1Kg weight falls through 1 metre by force of gravity.metre by force of gravity.
– Joule is to replace the calorie as the unit of Joule is to replace the calorie as the unit of energy.energy.
– The joule is smaller than the dietary The joule is smaller than the dietary calorie, hence dieticians use Kilojoulecalorie, hence dieticians use Kilojoule Calorie X 4.184 = KilojouleCalorie X 4.184 = Kilojoule
Concentration of Concentration of substancessubstances
MoleMole– this is the amount of substance present in a this is the amount of substance present in a
given volume of one litre.given volume of one litre.
– body function relies upon a balanced body function relies upon a balanced concentration of many different substances. They concentration of many different substances. They form the basis for biochemical testsform the basis for biochemical tests
– within a population, a normal concentration of within a population, a normal concentration of particular substances have been determined for particular substances have been determined for many body chemicalsmany body chemicals..
MilliequivalentMilliequivalent
– A milliequivalent is determined by relating the ability of A milliequivalent is determined by relating the ability of an element to combine with, or displace, hydrogen.an element to combine with, or displace, hydrogen.
– 1 milliequivalent of one substance does not necessarily 1 milliequivalent of one substance does not necessarily contain the same number of particles as 1 contain the same number of particles as 1 milliequivalent of another substance.milliequivalent of another substance.
– This measurement is found in diagnostic results, and for This measurement is found in diagnostic results, and for the concentration of particles in intravenous fluid the concentration of particles in intravenous fluid therapy. therapy.
Concentration of substances
Concentration of Concentration of substancessubstances
Weight-volumeWeight-volume– prior to the introduction of SI units, prior to the introduction of SI units,
substances were sometimes substances were sometimes expressed as number of grams per expressed as number of grams per 100 ml of water100 ml of water
– this is the same as percentage this is the same as percentage solution, such as 5% dextrose IV solution, such as 5% dextrose IV fluidsfluids
Calculation skills required of the nurse
Addition and subtractionAddition and subtraction Multiplication and division (able to use conversion Multiplication and division (able to use conversion
factors)factors) Percentages, ratios, proportionsPercentages, ratios, proportions Deal with fractionsDeal with fractions Deal with decimal pointsDeal with decimal points Able to convert one system of units into another Able to convert one system of units into another
(imperial units into metric units for weight, length)(imperial units into metric units for weight, length) Able to convert metric unitsAble to convert metric units Able to use formulae and equationsAble to use formulae and equations Able to use and interpret charts (nomogram, growth, Able to use and interpret charts (nomogram, growth,
BMI)BMI)
Moving and HandlingMoving and Handling Specific weight assessmentSpecific weight assessment
– Weight of a patient is usually in Grams or Kilograms, Weight of a patient is usually in Grams or Kilograms, although many people still relate to the Imperial although many people still relate to the Imperial measurement of stones and pounds. You will need to measurement of stones and pounds. You will need to know the conversion factor, and hence be able to know the conversion factor, and hence be able to have the have the arithmetical skill of multiplication:arithmetical skill of multiplication:
– conversion factor conversion factor if 1Kg =2.2 imperial poundsif 1Kg =2.2 imperial pounds 14pounds =1stone 14pounds =1stone
– Moving and Handling regulations provide guidelines Moving and Handling regulations provide guidelines on safe working loads you should handle.on safe working loads you should handle.
Moving and HandlingMoving and Handling Lifting loads in standing position (max weight 15 Kg for men)Lifting loads in standing position (max weight 15 Kg for men) Lifting loads in a sitting position (for women 3 Kg)Lifting loads in a sitting position (for women 3 Kg) Pushing or pulling loads (starting force for women 16Kg or160 Pushing or pulling loads (starting force for women 16Kg or160
Newtons)Newtons)
When pushing or pulling clients on beds, wheelchairs or When pushing or pulling clients on beds, wheelchairs or loads, you will need to understand biomechanics, i.e force, loads, you will need to understand biomechanics, i.e force, vector analysis, centre of gravity, base, frictionvector analysis, centre of gravity, base, friction
Knowledge of biomechanics are useful in orthopaedics, Knowledge of biomechanics are useful in orthopaedics, physiotherapy, moving and handling, pressure damage physiotherapy, moving and handling, pressure damage preventionprevention
Moving and HandlingMoving and Handling Specific patient risk assessment may require you to Specific patient risk assessment may require you to
calculate the Body Mass Indexcalculate the Body Mass Index Height/ weight = numeric scoreHeight/ weight = numeric score
Certain score ranges indicate whether the person is Certain score ranges indicate whether the person is obese, normal weight or underweightobese, normal weight or underweight
Height measurements are usually in metres but Height measurements are usually in metres but some patients still think in imperial units of feet and some patients still think in imperial units of feet and
inchesinches, , you may have to convert into metres.you may have to convert into metres.
Drug AdministrationDrug Administration TabletsTablets
– these may come in dosages of micrograms, milligrams or gramsthese may come in dosages of micrograms, milligrams or grams CapsulesCapsules
– these may again come in dosages such as abovethese may again come in dosages such as above Elixirs, syrups, Emulsions, LinctusElixirs, syrups, Emulsions, Linctus
– usually measured in mg/ml or microgram/mlusually measured in mg/ml or microgram/ml InjectionsInjections
– usually measured as mg/ml or microgram/ml (also measured in units)usually measured as mg/ml or microgram/ml (also measured in units) InhalersInhalers
– measured as micrograms/ puffmeasured as micrograms/ puff Topical medicationTopical medication
– these may be measured as %/ ml as in eye drops, or mg, micrograms these may be measured as %/ ml as in eye drops, or mg, micrograms per patchper patch
FluidsFluids– these are usually prescribed as weight-volume, although these are usually prescribed as weight-volume, although
milliequivalents and millimoles may be on the packaging of the milliequivalents and millimoles may be on the packaging of the product.product.
Drug AdministrationDrug Administration
Household measuresHousehold measures– these are used when calibrated devices are these are used when calibrated devices are
not available. Household utensils are used not available. Household utensils are used in the home setting.in the home setting.
– 1 teaspoon = 4-5 ml1 teaspoon = 4-5 ml– 1 tablespoon = 15 ml1 tablespoon = 15 ml
Apothercaries’ systemApothercaries’ system– this has been largely replaced by the metric this has been largely replaced by the metric
system but is still used occasionally (e.g system but is still used occasionally (e.g fluid ounces)fluid ounces)
Paediatric Drug Paediatric Drug CalculationsCalculations
The dosage of many drugs is smaller than of the same drug for The dosage of many drugs is smaller than of the same drug for an adult.an adult.
Calculations are based on the amount of the drug per kilogram of Calculations are based on the amount of the drug per kilogram of body weight or on body surfacebody weight or on body surface
Estimating body surface area can be done using the West Estimating body surface area can be done using the West NomogramNomogram
Clark’s formula can be used to determine whether the prescribed Clark’s formula can be used to determine whether the prescribed dose seems reasonable based upon the weight of the childdose seems reasonable based upon the weight of the child
Young’s formula, based on the age of the child, can give you the Young’s formula, based on the age of the child, can give you the child’s equivalent dosage to an adult dosage for a drugchild’s equivalent dosage to an adult dosage for a drug
Infection ControlInfection Control
AntisepticsAntiseptics– expressed as % w/v e.g 1% w/v iodine in aquous expressed as % w/v e.g 1% w/v iodine in aquous
solutionsolution DisinfectantsDisinfectants
– this may be expressed in grams tablets that this may be expressed in grams tablets that require dissolving in water. For x 7 ActiChloride require dissolving in water. For x 7 ActiChloride 2.5g tablets, there will be 10,000 parts per 2.5g tablets, there will be 10,000 parts per million chlorine available when dissolved in 1 million chlorine available when dissolved in 1 litre of waterlitre of water
– spray disinfectants may be expressed as % w/v spray disinfectants may be expressed as % w/v e.g Dispray chlorhexadine gluconate 0.02% e.g Dispray chlorhexadine gluconate 0.02% w/v w/v ( 0.2mls of chlorahexadine gluconate ( 0.2mls of chlorahexadine gluconate is diluted in 1 litre of water) is diluted in 1 litre of water)
Biochemical ResultsBiochemical Results A knowledge of volume, weight, length, time, A knowledge of volume, weight, length, time,
amount of substance, osmolality is required:amount of substance, osmolality is required: Arterial Blood gasesArterial Blood gases
– PaCOPaCO22 35-45 35-45 mmHmmHgg
– PaOPaO22 >80 >80 mmHgmmHg Chloride is measured as mEq/LChloride is measured as mEq/L cholestrol is measured as mg/dLcholestrol is measured as mg/dL serum cortisol as µg/dLserum cortisol as µg/dL urine cortisol as µg/24 hrurine cortisol as µg/24 hr serum osmolality as mOsm/kgserum osmolality as mOsm/kg urine osmolality as mOsm/Lurine osmolality as mOsm/L
Haemotology ResultsHaemotology Results A knowledge of volume, weight, length, time and A knowledge of volume, weight, length, time and
percentage is required.percentage is required. Red Blood Cells (RBC) is measured as X 10Red Blood Cells (RBC) is measured as X 10 (-6) (-6) /cubic /cubic
mmmm Haemoglobin (Hb) is measured as g/dlHaemoglobin (Hb) is measured as g/dl Platelet count is measured in % or parts per 100Platelet count is measured in % or parts per 100 Sedimentation Rate is measured in mm/hrSedimentation Rate is measured in mm/hr MCV is measured in microgram/ cubic metre or ųMCV is measured in microgram/ cubic metre or ų-3-3mm There are many more constituents to blood but all There are many more constituents to blood but all
use the above units of measurementsuse the above units of measurements
Public Health ResultsPublic Health Results
Nutritional AssessmentNutritional Assessment The following units of measurement will be The following units of measurement will be
important for the dietician:important for the dietician:– anthropemetric measurements anthropemetric measurements (height, weight, (height, weight,
skinfold thickness and muscle mass)skinfold thickness and muscle mass)
– weight of the client in Kgweight of the client in Kg– height of the client in order to determine the BMIheight of the client in order to determine the BMI– volume of fluids intake/output measured in Lvolume of fluids intake/output measured in L– energy in joules or calories given by food energy in joules or calories given by food – constituent of food, such as carbohydrates, constituent of food, such as carbohydrates,
proteins, fat, minerals and vitaminsproteins, fat, minerals and vitamins– food constituents are measured in g, mg or µgfood constituents are measured in g, mg or µg
Growth and DevelopmentGrowth and Development
Percentile charts are statistical charts Percentile charts are statistical charts indicating normal distribution of weight and indicating normal distribution of weight and height for age categories of children’s growth height for age categories of children’s growth within a given population.within a given population.
Hence you will have to become familiar with Hence you will have to become familiar with the concept of percentiles in statistics, and the concept of percentiles in statistics, and measuring weight and height of children (Kg measuring weight and height of children (Kg and cm)and cm)
Blood PressureBlood Pressure
Although the S.I unit is the Pascal, with Although the S.I unit is the Pascal, with traditional mercury sphygnometers the traditional mercury sphygnometers the measurement is in mmHg. measurement is in mmHg.
Invasive monitoring of blood pressure may be Invasive monitoring of blood pressure may be measured in pascalsmeasured in pascals
You will rarely have to convert one unit of You will rarely have to convert one unit of measurement into another but you will need to measurement into another but you will need to be aware of what normal limits are for the be aware of what normal limits are for the client of a given age if readings are in pascal, client of a given age if readings are in pascal, as well as mm of mercury (Hg)as well as mm of mercury (Hg)
PulsePulse
This is usually measured as the number of This is usually measured as the number of pulsatile beats per minute e.g 60 beats for pulsatile beats per minute e.g 60 beats for every secondevery second
The pulse should be measured over a full The pulse should be measured over a full second to obtain an accurate number of beatssecond to obtain an accurate number of beats
Respiration and ventilationRespiration and ventilation
Respiration is measured over a full minute or 60 seconds Respiration is measured over a full minute or 60 seconds by the nurse.by the nurse.
Other observational factors are considered, such as the Other observational factors are considered, such as the breathing pattern, noise of inhalation etc.breathing pattern, noise of inhalation etc.
Ventilation of patients occur in critical care settings with Ventilation of patients occur in critical care settings with
respiratorsrespirators.. There are negative and positive respirators according to There are negative and positive respirators according to
whether they are helping with inhalation or exhalationwhether they are helping with inhalation or exhalation.. Pressure > than standard atmospheric pressure (101kPa Pressure > than standard atmospheric pressure (101kPa
or 760mmHg) is often referred to as positive or 760mmHg) is often referred to as positive pressure,and those < than standard atmospheric pressure,and those < than standard atmospheric pressure is referred to as negative pressure ventilators.pressure is referred to as negative pressure ventilators.
Body TemperatureBody Temperature
Body temperature is usually measured in CelsiusBody temperature is usually measured in Celsius The Farenheit scale of 32 to 212 F encompasses the The Farenheit scale of 32 to 212 F encompasses the
same temperature range as 0 to 100 Celsius scale. same temperature range as 0 to 100 Celsius scale. – Conversion of Farenheit into celsius:Conversion of Farenheit into celsius:
C=C= 55 (F-32) (F-32) e.g 37C = e.g 37C = 5 5 (98-32) =(98-32) =55(66)=36.6 (66)=36.6 9 9 9 9 9 9
– Conversion of Celsius into Farenhet is done by:Conversion of Celsius into Farenhet is done by:
F =F = 9 9 (C) + 32 (C) + 32 5 5
Relevance of measurements to Relevance of measurements to some nursing intervention sessionssome nursing intervention sessions
Infection ControlInfection Control– concentration of chemicals for antiseptics, disinfectantsconcentration of chemicals for antiseptics, disinfectants
HygieneHygiene– concentration of chemicals in mouth washes, toothpaste, creamsconcentration of chemicals in mouth washes, toothpaste, creams
HandwashingHandwashing– chemical concentration in soaps, alcohol rubschemical concentration in soaps, alcohol rubs
OxygenationOxygenation– blood gases, oxygen saturations, flow rates of oxygen, peak flow blood gases, oxygen saturations, flow rates of oxygen, peak flow
measurementsmeasurements Eating and drinkingEating and drinking
– energy value of food, flow rates of feeds, fluid balance chartsenergy value of food, flow rates of feeds, fluid balance charts EliminationElimination
– urinary output, catheter balloonsurinary output, catheter balloons Skin integritySkin integrity
– pressure of blood capillary occlusion, pressure relieving productspressure of blood capillary occlusion, pressure relieving products
ConclusionConclusion The most important area for The most important area for numeracy skills is in drug numeracy skills is in drug
administrationadministration
Understanding some scientific concepts will help you understand why Understanding some scientific concepts will help you understand why some interventions are undertaken in a particular way e.g moving and some interventions are undertaken in a particular way e.g moving and handlinghandling
In the areas of paediatrics, neonatal care, intensive and critical care, In the areas of paediatrics, neonatal care, intensive and critical care, accurate drug calculations are required for drug administrationaccurate drug calculations are required for drug administration
High standards of drug administration is required at all timesHigh standards of drug administration is required at all times
An understanding of other S.I units, such as millimoles, will enable youAn understanding of other S.I units, such as millimoles, will enable you to understand the consequences of your nursing to understand the consequences of your nursing interventionintervention
REFERENCESREFERENCESJ.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