Numeracy for Drug Calculations

270 Pages·2011·1.876 MB·English

by  Kerri Wright

Drug Calculations for Nurses
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Drug Calculations for Nurses
Context for Practice
Kerri Wright
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© Kerri Wright 2011
All rights reserved. No reproduction, copy or transmission of this
publication may be made without written permission.
No portion of this publication may be reproduced, copied or transmitted
save with written permission or in accordance with the provisions of the
Copyright, Designs and Patents Act 1988, or under the terms of any licence
permitting limited copying issued by the Copyright Licensing Agency,
Saffron House, 6–10 Kirby Street, London EC1N 8TS.
Any person who does any unauthorized act in relation to this publication
may be liable to criminal prosecution and civil claims for damages.
The author has asserted her right to be identiied as the author of this work
in accordance with the Copyright, Designs and Patents Act 1988.
First published 2011 by
PALGRAVE MACMILLAN
Palgrave Macmillan in the UK is an imprint of Macmillan Publishers Limited,
registered in England, company number 785998, of Houndmills, Basingstoke,
Hampshire RG21 6XS.
Palgrave Macmillan in the US is a division of St Martin’s Press LLC,
175 Fifth Avenue, New York, NY 10010.
Palgrave Macmillan is the global academic imprint of the above companies
and has companies and representatives throughout the world.
Palgrave® and Macmillan® are registered trademarks in the United States,
the United Kingdom, Europe and other countries.
ISBN: 978–0–230–23161–0
This book is printed on paper suitable for recycling and made from fully
managed and sustained forest sources. Logging, pulping and manufacturing
processes are expected to conform to the environmental regulations of the
country of origin.
A catalogue record for this book is available from the British Library.
10 9 8 7 6 5 4 3 2 1
20 19 18 17 16 15 14 13 12 11
Printed in China
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Contents
List of Figures and Boxes vii
Acknowledgements viii
Introduction x
List of Abbreviations xviii
PART I – DRUG CALCULATIONS IN CONTEXT
1 Back to Basics! Calculating and understanding simple
medicine dosages 3
Units of Measurement 3
Formulations 6
Labelling of Medications 7
Checking 12
Converting 19
Units 28
Ratios 28
Dosage per Weight 30
Divided Doses 34
Chapter Summary 35
References 37
2 The Next Step! Medicines expressed as weight/volume
strengths 39
Weight/Volume 39
Halving Method 45
Doubling 48
Reducing Down to a Single Unit 51
Relationships 54
Syringes 58
Preilled Syringes 61
The Nursing Formula 62
Complex Questions using Weight and Volume 73
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vi Contents
Chapter Summary 80
References 83
3 The Final Step! Calculations involving continuous infusions 85
Infusions 85
Fluid Replacement Therapy 88
Volumetric Infusion Devices 90
Manual Infusions 92
Percentages 103
Syringe Pumps 108
Dosage per Hour 114
Sliding Scales 117
Infusion Dosages per Weight 118
Syringe Drivers 125
Chapter Summary 133
PART II – PRACTICE AND ASSESSMENT
4 Maths Fitness Programme! Practice, practice, practice 139
Introduction 139
Test Your Maths Skills 140
Session One – Maths Fitness 143
Session Two – Maths Stamina 151
Session Three – How Supple Are You? 166
Session Four – Through the Pain Barrier! 174
Session Five – Running the 5K Maths Challenge! 180
5 How much have I learnt? A chance to evaluate your learning 183
Answers 215
Index 247
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List of Figures and Boxes
Figures
1 Medications and the dosages expressed as weight/volume or
weight for elixir, ampoules and tablets 7
2 Illustration of a medicine packet and labelling 7
3 Medicine labelled for an individual person 8
4 A side view of a medicine box showing the expiry date and batch
number 8
5 An example of a medicine administration chart 9
Diagram illustrating how to estimate the amount of solution to
administer 14
6 Illustrating the relationship between grams and milligrams 21
7 A normal syringe end and a syringe with a leur lock 40
8 Demonstration of how a weight/volume dosage is ‘manufactured’ 41
9 Patient requires only 5mg from the 20mg/2ml ampoule 44
10 A solution containing 10g/100ml 45
11 A visual representation of 10mg/0.5ml 56
12 Visual representation of 50mg in 2ml 57
13 Common syringes used in healthcare 59
14 A 1ml syringe showing the measurements and dosage of a
10mg/ml strength solution and indicating the volume containing
an 8mg dose 60
15 Illustration of the reconstitution of 600mg benzypenicillin
with 10ml water for injection 77
16 Diagram showing difference in plasma concentration levels
between bolus and continuously infused drugs 86
17 Illustration of a burette in practice 88
18 An illustration of rate per hour for a 1000ml infusion bag
prescribed over 10 hours 89
19 A giving set packet showing the number of drops/ml 93
20 Intravenous medicine administration chart 99
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viii List of Figures and Boxes
21 Illustration of how a 5% infusion is ‘made’ 104
22 A syringe showing rate of millilitres/hr 109
23 A syringe showing 20mls set at 4ml/hr 110
24 Illustration of how to set up the syringe for a syringe pump 112
25 Diagram showing a 10ml syringe with the volume measuring
48mm for a syringe driver 126
Boxes
i Sample solution xiv
1 Common measurements used in drug dosages, with abbreviations 3
2 Measurement types and explanations 4
3 Common formulations for drugs 6
4 Summary of the common routes, abbreviations and usual dose
for this route 11
5 Checking your solution to drug calculations 13
6 Conversion 20
7 Step by step guide – calculating number of tablets or ampoules to
administer 26
8 Explanation of dosages used for adrenaline 29
9 Step by step guide – calculating number of tablets or ampoules to
administer when prescribed as dose per weight 33
10 Syringes 40
11 Visual representation of relationship between prescribed dose
and available dose 55
12 Long division procedure for the sum 31 divided by 10 66
13 Step by step guide to solving weight volume calculations 74
14 Different types of electronic devices for infusions 86
15 Illustration of the drip rate compared to seconds 102
16 Common rates for continuous intravenous infusions 102
17 An example of an insulin sliding scale 117
18 Similarities and differences between a syringe pump and a
syringe driver 125
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Acknowledgements
I would like to thank the following people for their help with reading and
checking through early drafts of this book; Cathy Maylin, Anita Lutchman,
Terry Ferns and Philip Marini. I would also like to thank all my colleagues at
University of Greenwich who have readily given their time to help me in my
research on this topic and the students who have been enthusiastic recipi-
ents of my teaching and ideas and have continually inspired me to rethink
and reine my thoughts. Finally, I’d like to thank Professor Liz Meerabeau
who has been a constant encouragement and believer in my work on drug
calculations, Pat Williams for her love and compassion and Kate Llewellyn,
Project Editor, who has been a patient and thoughtful motivator throughout
this project. However, my acknowledgements would not be complete
without heartfelt thanks to my partner Joanna and our daughter Bethany;
to them the thanks are for everything.
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