Calibration: Why is it important?

One of the key questions for any Care Quality Commission inspection is ‘Is this practice safe?’ This means that inspectors will be looking for evidence of reliable systems, processes and practices to keep people safe – and this includes proper maintenance of the equipment used in everyday practice

Practice nurses use a variety of instruments and devices in their daily working life with the results obtained used to guide treatment options or may in some cases necessitate the need to refer on to a GP for further advice. Medical devices therefore play a key role in health care: they are vital for diagnosis, therapy, monitoring, rehabilitation, and it is essential that equipment is properly maintained to ensure high-quality, effective and – critically – safe patient care. Ensuring that all practice equipment – from the humble thermometer to the ECG machine – is functioning as the manufacturer intended is essential for clinical and financial governance, and to minimise the risk of adverse events.¹ It is also important that any equipment used is accurate to avoid the potential for patients to receive at best unnecessary treatment and at worst, incorrect diagnosis of a serious medical condition. This article therefore looks at what needs to be calibrated and why this is so important.

WHAT IS CALIBRATION?

Calibration is the process of checking and adjusting the internal accuracy of any device. It involves comparing the measurements of the device being tested (e.g a thermometer or sphygmomanometer) against those from an accurate reference device, and if different, adjusting the output of the test device to match that of the reference device.²

GENERAL PRACTICE RESPONSIBILITY

The Care Quality Commission (CQC) carries out a rolling programme of inspections in general practice to ensure that the service provided is, among other criteria, safe. One way that they do this is to look for evidence – i.e. records – to show that any equipment used is maintained and not out-of-date. Equipment that may have a fixed lifespan includes, for example, needles, syringes and defibrillator pads. The CQC states – unambiguously – that if these are out-of-date they are unsafe to be used. And if out-of-date equipment is present in the practice it could be used.

GP practices are responsible for ensuring that all medical devices are maintained appropriately, and this includes calibration, reconditioning and refurbishment. Inaccurate readings from faulty or poorly calibrated machines can impact on quality of care and treatment; for example, errors in blood pressure measurement could result in patients receiving treatment they do not need if it is overestimated, or increasing their clinical risk if it is underestimated and left untreated.³

Equipment that should be subject to regular checks includes fridges used to store medicines (vaccines), including fridge thermometers; other thermometers; nebuliser compressors; spirometers; pulse oximeters; sphygmomanometers; weighing scales; and electronic ear irrigators. ECG machines, Doppler ultrasound equipment and CO monitors also need to be calibrated and maintained.

Sphygmomanometers

Measuring and recording blood pressures is a frequently performed task for practice nurses and is used for both the diagnosis and monitoring of hypertension and also for the assessment of response to treatment. The consequences of using poorly maintained equipment is therefore potentially very serious and could lead to patients receiving treatment which they do not need, or conversely having treatment discontinued. Ambulatory blood pressure monitory is now the gold standard for diagnosis of hypertension, however for those patients who cannot tolerate the equipment or where the equipment is not available the alternative is home monitoring. General advice is for the patient to record their blood pressure twice daily (morning and evening) for a week if possible. Some patients also like to monitor their blood pressure at home irrespective of whether they need to do so and advice from the Blood Pressure Association is to make sure that the home blood pressure monitor chosen has been listed as ‘clinically validated’ for accuracy by the British Hypertension Society.⁴ Recommendations for suitable monitors, the frequency of servicing and calibration and who can perform this should be available from the manufacturer.

Thermometers

Thermometers in general practice are in frequent and regular use and in recent years, mercury thermometers have been replaced with digital thermometers because of the dangers posed by mercury, which according to the World Health Organization is associated with potential damage to the environment, human toxicity and a risk to health – and which also carries a high cost for disposal.⁵ Many digital thermometers will display an error message if the thermometer is not functioning properly. The manufacturer may suggest when calibration should be undertaken (i.e yearly or two yearly) but it is generally recommended that calibration takes place annually.

Fridges for vaccine storage

The administration of vaccines to both adults and children is an important part of the practice nurse role. The ‘cold chain’ is the term applied to the process used to maintain optimal conditions during the transport, storage, and handling of vaccines, and begins at the manufacturing stage and ends with the administration of the vaccine to the client. The fridge used for storage of vaccines should be a validated vaccine fridge. Those used for domestic food storage are unsuitable. The optimum temperature for refrigerated vaccines is between +2°C and +8°C and for vaccines to be effective, they must be stored within this temperature range to ensure that they retain their potency. Maintenance to ensure the fridge is working effectively should include making sure the fridge is clean, and there should also be a contract in place to cover servicing and calibration of the temperature gauge. The fridge temperature should also be checked and recorded daily. A protocol for recommended practice for temperature monitoring is shown in Table 1. All vaccine fridges should be subject to annual inspection/servicing and service logs maintained.⁶

ECG machines

Many practices now have an electrocardiogram (ECG) machine which is a useful tool for measuring the electrical activity of the heart, recording the heart’s rhythm and activity. It is therefore extremely useful in detecting abnormalities and irregular heart rhythms. It can also be useful in detecting whether the patient has had a heart attack, either in the past or quite recently and can also help diagnose an enlarged heart. Accuracy of equipment is therefore crucial to avoid diagnostic errors. Most modern ECG machines calibrate themselves when they are turned on, but older or cheaper models may need prompting. The user manual for the individual machine should give information relating to this, but in general, guidance recommends calibration by a qualified technician at six monthly intervals to ensure accuracy is maintained.⁷

Pulse oximeter

Pulse oximeters measure oxygen saturation levels, the term used to describe the concentration of oxygen in the blood and the device measures the percentage of haemoglobin binding sites in the bloodstream occupied by oxygen. Low oxygen levels can occur in association with a number of medical conditions, including anaemia, COPD, emphysema, pneumonia, pulmonary embolism, fibrosis and pulmonary oedema.⁸ Normal oxygen saturation values are 97% to 99% in the healthy individual, and an oxygen saturation value of 95% is clinically accepted in a patient with a normal haemoglobin level.⁹ Pulse oximeters are calibrated during manufacture of the device and automatically check their internal circuits when they are turned on and are accurate to +/-2% in the range of saturations of 70 to 100%, but become less accurate when saturation levels are below 70%.¹⁰ They require calibration in accordance with the manufacturer’s guidance, usually annually.

Dopplers

Many practice nurses are now trained in the use of Doppler ultrasound, which is frequently used as a diagnostic tool when assessing patients for arterial disease. The procedure is now considered mandatory as part of a leg ulcer assessment.¹¹ It can indicate the presence and severity of arterial disease,12 and results can guide the practitioner in deciding whether or not the use of compression bandaging is appropriate. Equipment accuracy is therefore absolutely vital as inaccurate results could potentially lead to inappropriate application of compression with potentially disastrous results, resulting in possible limb loss.¹³ Calibration by a qualified technician is generally required annually.

Spirometer

Spirometry has become widely used in general practice and many nurses are now trained in its use and in the interpretation of the findings. It is an extremely useful tool for the assessment of lung function and is used for the diagnosis and monitoring respiratory diseases, especially asthma and COPD. Calibration checks must be carried out with all types of spirometer as a daily routine on each day of use and a log should be kept for medico-legal purposes.¹⁴ A 3 litre syringe is recommended for assessing accuracy of the spirometer before use. Guidance suggests that the syringe used to calibrate spirometers must have an accuracy of 15 ml or 0.5% of the full scale (15 ml for a 3l syringe), and the manufacturer must provide recommendations concerning appropriate intervals between syringe calibration checks.¹⁴ It is also important to store the calibration syringe appropriately. It should be stored and used in such a way as to maintain the same temperature and humidity as the testing site, best achieved by keeping the syringe in close proximity to the spirometer, but out of direct sunlight and away from heat sources.¹⁴ In addition to calibration checks, quality control measures should also be in place to ensure best practice. (See Box 1)

Weighing scales

The weighing of patients is undertaken for a number of reasons, such as monitoring weight changes and calculating drug dosages. Following an extensive audit of healthcare premises, it was discovered that scales used for weighing patients were frequently incorrectly calibrated or in some cases an inappropriate type of scale was being used. There are currently two types of scales in use.

• Class III are recommended for use in healthcare premises for the calculation of medication, treatment, and monitoring.
• Class IIII are of the type used in domestic settings. If this type is in use in practice, it should be replaced with scales of Class III or higher.

All scales should only display a metric reading. If switchable (i.e. between metric and imperial readings) are in use, the switching facility must be disabled. Class IIII scales should be used for monitoring and recording patients’ weights and are not appropriate for calculating the dose of medication, or weighing any one under the age of 18.¹⁵

Equipment should be tested annually, but if it is suspected that it may be giving inaccurate readings, it should be taken out of use until it has been tested.¹⁵

CO monitors

CO monitors measure the concentration of carbon monoxide (CO) in expired air and are an easy, noninvasive, and immediate way of assessing a patient’s smoking status.¹⁶ Practice nurses may find these useful in smoking cessation clinics as measurements should decrease over time once the patient has quit, reverting to non smoking levels.¹⁷ (Table 2) However, they must be accurately calibrated to be useful.

CONCLUSION

Practice nurses have a duty of care to patients to ensure any equipment they are using is accurate and fit for purpose, and every practice should have an effective strategy in place to ensure that all equipment in use is maintained and calibrated at regular intervals.

Any instrument suspected of giving inaccurate readings should be recalibrated before further use. Only if this is adhered to can practice nurses be sure the care they give is best practice.

REFERENCES

1. MHRA. Managing Medical Devices. http://www.dhsspsni.gov.uk/dbni-2014-02.pdf

2. United Nations development programme. Guidance on maintaining and calibrating non-mercury clinical thermometers and sphygmomanometers. http://noharm.org/lib/downloads/mercury/Guidance_Hg_2013.pdf

3. Care Quality Commission. CQC Mythbuster 34: Maintenance of medical equipment. http://www.cqc.org.uk/content/gp-mythbuster-34-maintenance-medical-equipment

4. Blood Pressure Association. How to choose the right blood pressure monitor. http://www.bloodpressureuk.org/BloodPressureandyou/Homemonitoring/Choosingyourmonitor

5. World Health Organization. Replacement of mercury thermometers and sphygmomanometers in health care. http://whqlibdoc.who.int/publications/2011/9789241548182_eng.pdf

6. The Green Book. Storage, distribution and disposal of vaccines, 2015. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/223753/Green_Book_Chapter_3_v3_0W.pdf

7. Ministry of Health and Family Welfare (2010) Medical equipment maintenance manual. Available at: http://rice360.rice.edu/Resources/BIOE449/MedicalMaintenance_suctionPump_oxygen%20conecntrator.pdf

8. Mayo Foundation for Medical Education and Research. Hypoxaemia: Low blood oxygen. Available at: http://www.mayoclinic.org/symptoms/hypoxemia/basics/causes/sym-20050930

9. Schutz SL. Oxygen Saturation Monitoring by Pulse Oximetry. In: AACN Procedure manual for Critical Care, Fourth Edition WB Saunders. Available at: http://www.aacn.org/WD/Practice/Docs/ch_14_PO.pdf

10. Fearnley SJ. How does a pulse oximeter work. Available at: http://www.favoriteplus.com/pulse-oximeter.php

11. Vowden, K. and Vowden, P. (2001a). Doppler and the ABPI: how good is our understanding. Journal of Wound Care. Vol. 10. No. 6. Pp197-202

12. Vowden. P. and Vowden, K. (2001b) Doppler assessment and ABPI: Interpretation in the management of leg ulceration. www.worldwidewounds.com

13. Moffatt, C. and O’Hare, L. (1995). Ankle pulses are not sufficient to detect impaired arterial circulation in patients with leg ulcers. Journal of Wound Care. Vol. 4. No. 3. Pp 134-138

14. Miller, M.R. et al (2005) ATS/ERS task force: standardisation of lung function testing: standardisation of spirometry. European Respiratory Journal; 26: 2, 319–338.

15. Department of Health, Health Facilities Scotland, Health, Social Services and Public Safety. Estates and facilities alert: Patient weighing scales, 2010. http://www.dhsspsni.gov.uk/efa-2010-001a.pdf

16. Middleton ET, Morice AH. Breath carbon monoxide as an indication of smoking habit. Chest. 2000;117(3):758-763.

17. Covita. Breath Carbon Monoxide Monitor – the Stethoscope of Smoking Cessation. http://www.integration.samhsa.gov/pbhci-learning-community/smokerlyzer_guide.pdf

18. GP homepage. Carbon monoxide monitoring in smoking cessation. http://www.gpnotebook.co.uk/simplepage.cfm?ID=x20091016143731248233

19. Public Health England. Protocol for ordering, storing and handling vaccines. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/300304/ Protocol_for_ordering__storing_and_handling_vaccines_March_2014.pdf