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