If you are confident in your basic numeracy skills but want to learn how to apply these to the clinical setting, concentrate on Chapters 3 to 6. These will equip you with information about the SI system used in healthcare, how to calculate drug doses and the use of numbers and calculations in other areas of clinical practice like nutrition and fluid balance. Chapter 6 contains several tests so you can check your knowledge and understanding.
If you are an experienced nurse and have changed career directions and are unsure whether your current knowledge of drug and clinical calculations is up to scratch, then focus your study on Chapters 3, 4 and 6. This will allow you to revise the SI system and practise calculating drug doses and other clinical calculations.
If you are confident in your basic numeracy skills but want to gain more practice of drug calculations then concentrate your efforts on Chapters 3, 4 and 6. These focus mainly on drugs, the units of measurement and calculating correct doses.
If you are revising for a drug calculation exam, focus on Chapters 3, 4 and 6. These chapters explain the SI system and the fundamentals of calculating drug doses as well as providing many clinically related practice calculations.
NUMERACY AND CALCULATION SKILLS IN THE CLINICAL ENVIRONMENT
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concentrates on why you need calculation and numeracy skills
considers common sources of drug and calculation errors
identifies the various opportunities available to help you learn (or re-learn) the necessary calculation skills.
has a self-assessment test at the end, so that you can identify your strengths and diagnose your weaknesses.
1.1 Why you need to know about numbers and calculations
As a nurse, you will be required to deal with numbers and perform basic calculations every day, for example:
ensuring accurate administration of drugs
completing a fluid balance chart
calculating a BMI.
It is therefore absolutely crucial, for you and for your patients, that you become confident in handling numbers and familiar with the calculations you will come across in your practice. By doing this, you will help to ensure that your patients get the best and safest care possible from the healthcare services and from you. Nursing is, in part, about ‘doing things right and doing the right things’ and drug and clinical calculations are an integral part of everyday nursing. ‘Doing things right’ is about ensuring the accuracy of your calculations, and ‘doing the right things’ is then applying your numeracy and calculation skills to the variety of situations that depend on it.
The Nursing and Midwifery Council (NMC) consider numeracy skills to be a fundamental part of the role of the nurse. They have produced a group of skill statements (Essential skills clusters) in addition to the outcomes and proficiencies that students have to achieve, targeted on aspects of care that if not performed competently would put patients at risk. The Essential skills clusters make it clear that the ability to perform calculations and interpret data go beyond administering medicines and include baseline patient assessments, and nutritional and fluid support.
To register with the NMC, students will be assessed theoretically and in practice and must achieve 100% in a test of their numeracy skills. If you are already a Registered Nurse and are refreshing and updating your numeracy skills, this gives you a clear indication of the standards expected of new registrants and the level of skill that you need to achieve.
The UK population is ageing and so many of the patients you will deal with will be older and have complex needs; this frequently means that patients need more drugs, intravenous fluids and care assessments, all of which require numeracy and calculation skills. The Audit Commission (in their 2001 report Spoonful of Sugar) estimated that a typical Registered Nurse in an average district general hospital would spend about 40% of their time giving out medicines, even before taking account of other calculations such as fluid balance charts or weighing patients. In view of the changing needs of patients, the amount of time that nurses spend performing calculations is only likely to increase year by year.
Apart from the day-to-day performance in your health care role, you will need to be confident and familiar with calculations and numbers as many employers now use a numeracy test as part of the selection and recruitment process. In addition, mandatory annual updating and testing of numeracy skills is becoming a more common feature of nurses’ personal and professional development.
1.2 Common calculation errors
Whenever there is a calculation to be made, there is a possibility of an error. Knowing the situations where mistakes are more likely to be made and the type of calculation errors means that you are more alert to these possibilities, and hopefully less likely to fall into the trap.
Mistakes made with drug and clinical calculations usually involve:
getting the maths wrong
getting the dosage unit wrong
communication errors.
Getting the maths wrong
Chapter 2 deals with the mechanics of performing calculations and the use of decimal points as well as providing plenty of questions with which to test yourself.
A basic calculation mistake caused the death of a patient in Scotland in 2005. The nurse failed to get her dosage calculation checked by a colleague and she gave 40 units of insulin to a patient instead of the prescribed 4 units.
A mathematical miscalculation by two nurses working in a Leicestershire hospital caused the death of a baby in 2002. The nurses both made the same error with a decimal point, resulting in the baby receiving ten times more of a drug than was intended.
Getting the dosage unit wrong
Chapter 3 focuses on the SI system used throughout the UK. It is used to ensure that standardised sets of units are used for weights and volumes of medicines and fluids in healthcare.
In two separate Scottish nursing homes ‘International Unit’ had been shortened to ‘IU’. A prescription for 6 units of insulin became 61U, resulting in the patients receiving 61 units.
Communication errors
Communication is a vital part of healthcare and the quality and accuracy of writing is a source of calculation mistakes.
In 2005, a baby died in a Liverpool hospital after being given 15 000 units of the anticoagulant heparin instead of the prescribed 1500 units. The hand-written prescription read 1500U and the nurse mistook the ‘U’, wrongly used as an abbreviation for units, for a zero.
ERROR ALERT
Sometimes, what appears to be a drug calculation error isn’t.
At a West Midlands hospital in 2011, a nurse gave a patient ten times the amount of prescribed potassium chloride, an electrolyte that influences the heart rate and contraction. Predictably the patient suffered a fatal cardiac arrest.
The nurse had calculated the correct dose but did not get another nurse to witness the administration of the drug.
If another nurse had observed the administration (as demanded by the checking procedure), it would have become apparent that the infusion pump was set up wrongly, allowing it to give ten times the prescribed dose.
This catastrophic series of events, resulting in a patient death, was because of an administration error, not a calculation