Calculations in Health Care

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AIM

– To introduce the S.I units used in the field of nursing and medicine 

Learning outcomes

– – aware of some of the different units of measurements aware of numeric skills required by the nurse

Calculations in Health Care

 Fundamental SI units Physical Quantity Length Mass Time Current Temperature Name metre kilogram second ampere Kelvin Amount of substance mol cd mole Luminous intensity candela Symbol m Kg s A K

Calculations in Health Care

 Common derived units: Quantity Name Force Energy newton Pressure Potential difference volt joule pascal Frequency Volume hertz litre N V Symbol J Pa Hz L

Calculations in Health Care

 Names and abbreviations of SI unit multiples and sub multiples: Prefix Symbol mega kilo M k hecto h deca da Meaning Scientific notion one million one thousand one hundredth ten 10 (6) 10(3) 10(2) 10(1) deci centi milli d c m micro μ one tenth one hundredth one thousandth one millionth 10(-1) 10(-2) 10(-3) 10(-6)

Important S.I. units

       Kilogram – the gram is often used as the base unit in hospitals .

Litre – is used as the base unit for volume Kelvin – not used that much in nursing, rather it is the celsius Metre Second Joules – used by dieticians to measure energy from foods Millimoles – used to measure concentration of substances in fluids

Important non-SI units

 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  Column of mercury (mm Hg) – used extensively in measuring blood pressure with mercury and aneroid sphyghnometers  Milliequivalent – used to measure concentration of fluids

Weight 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

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

         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:

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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

   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)  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  Knowledge of biomechanics are useful in orthopaedics, physiotherapy, moving and handling, pressure damage prevention

Moving and Handling

  Specific patient risk assessment may require you to calculate the Body Mass Index Height/ weight = numeric score  Certain score ranges indicate whether the person is obese, normal weight or underweight  Height measurements are usually in metres but some patients still think in imperial units of feet and inches

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you may have to convert into metres.

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Drug Administration

Tablets – these may come in dosages of micrograms, milligrams or grams Capsules – these may again come in dosages such as above Elixirs, syrups, Emulsions, Linctus – usually measured in mg/ml or microgram/ml Injections – usually measured as mg/ml or microgram/ml (also measured in units) Inhalers – measured as micrograms/ puff Topical medication – these may be measured as %/ ml as in eye drops, or mg, micrograms per patch Fluids – these are usually prescribed as weight-volume, although milliequivalents and millimoles may be on the packaging of the product.

Drug Administration

  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 Apothercaries’ system – this has been largely replaced by the metric system but is still used occasionally (e.g fluid ounces)

Paediatric Drug Calculations

 The dosage of many drugs is smaller than of the same drug for an adult.

 Calculations are based on the amount of the drug per kilogram of body weight or on body surface  Estimating body surface area can be done using the West Nomogram  Clark’s formula can be used to determine whether the prescribed dose seems reasonable based upon the weight of the child  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

  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

        A knowledge of volume, weight, length, time, amount of substance, osmolality is required: Arterial Blood gases – – PaCO 2 PaO 2 35-45 mmH g >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

 A knowledge of volume, weight, length, time and percentage is required.

      Red Blood Cells (RBC) is measured as X 10 mm (-6) /cubic 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 -3 m There are many more constituents to blood but all use the above units of measurements

Public Health Results

Nutritional Assessment

 The following units of measurement will be important for the dietician: – – anthropemetric measurements skinfold thickness and muscle mass) weight of the client in Kg (height, weight, – – 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

 Percentile charts are statistical charts indicating normal distribution of weight and height for age categories of children’s growth within a given population.

 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

   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

 This is usually measured as the number of pulsatile beats per minute e.g 60 beats for every second  The pulse should be measured over a full second to obtain an accurate number of beats

Respiration and ventilation

     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 pressure ventilators.

Body Temperature

  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

 The most important area for numeracy skills is in drug administration  Understanding some scientific concepts will help you understand why some interventions are undertaken in a particular way e.g moving and handling  In the areas of paediatrics, neonatal care, intensive and critical care, accurate drug calculations are required for drug administration  High standards of drug administration is required at all times  An understanding of other S.I units, such as millimoles, will enable you understand the consequences of your nursing intervention to

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