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6Cs must end the years of make do and mend
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Although 90% of the 141,387 incidents were reported as causing no harm to the patient, 253 caused severe harm and 50 caused the patient’s death. Medication errors are most frequently due to the wrong dose, omitted or delayed medication or the wrong medication being administered (National Patient Safety Agency, 2009a). The most frequently cited wrong-dose error stems from calculation error.
Common errors by nurses include the following:
* Not understanding the units of measurements for medication, for example “nanograms” and “micrograms”;
* Using the wrong equipment to measure dosages;
* Making slips in calculations that result in the wrong dose or rate of medicine being administered (NPSA, 2009a; 2009b).
These errors can be the result of nurses not having the right knowledge or skills, or of other factors, such as distractions or stress. Medication errors occur across acute, community, general practice, learning disabilities and mental health clinical areas, so key calculation skills are applicable to all nurses (NRLS, 2012).
Units of measurement
Nurses need to understand the measurements used for drug dosages and be able to convert between these different units of measurement (Fig 1). Drugs are generally measured in one of three ways:
* According to the drug’s weight (grams, milligrams and micrograms for example);
* The volume (millilitres and litres);
* Standardised international units and strength of solutions when a weight of a drug is dissolved in a volume of liquid (for example milligrams per millilitre).
A number of medication errors have been made through not converting between different units of measurement correctly, resulting in doses of 10 or 100 times that prescribed (NPSA, 2009b). A number of fatalities have occurred when nurses have not understood how to measure insulin units, mistakenly measuring this in millilitres and administering large doses of insulin (NPSA, 2010).
Drugs are commonly prescribed or manufactured according to their weight, or the strength of a specific volume (weight per volume or “w/v”). The main weight measurements that nurses must be familiar and confident converting between are grams, milligrams, micrograms and nanograms. The relationship between each of these measurements is 1000. Conversions require nurses to multiply or divide dosages by 1000. It is important that conversions are checked carefully, through repeating the calculation or asking a colleague if unsure.
Once the conversion has been checked the prescribed dose can be compared with the available dose to calculate how much of the medicine to administer. For tablets, this type of calculation is usually quite straightforward, as the prescribed dose can be divided by the available drug dose to work out how many tablets to give. For example, if the prescription is 30mg prednisolone and the tablets available are 5mg, then the number of tablets to administer would be six. When the available dose is a solution with a...