Blood Pressure monitoring is one of the most common tests done in health care. It is considered a vital sign, thus routinely checked on almost every patient that seeks for treatments in healthcare centres. It helps in the diagnoses of wide range of diseases: from gastrointestinal diseases such as diarrhoea and many other cardiovascular diseases. It is therefore very paramount to the correct treatments of these diseases.
Overestimation and underestimation of blood pressure do not only lead clinicians to misdiagnoses, but also put patients under a lot of physiological, physical and psychological stress. Whiles underestimating a patient’s blood pressure may put one at risk of developing the complications associated with high blood pressure such as stroke and heart failure, overestimating can also burden one financially (in terms of medical costs) and psychologically.
Over the years, the mercury sphygmomanometer has been the commonest device that is used to monitor patient’s blood pressure and till today, it’s still considered the gold standard, when it comes to accuracy. Other devices available for measurement of blood pressure include the Aneroid Sphygmomanometer (a blood pressure monitoring device that contain no liquid) and the Automated

Digital Sphygmomanometer.

Though the use of Aneroid Sphygmomanometer seems to be gaining popularity among some countries and healthcare centres, it must be calibrated more frequently due to the fact they are more complex than mercury sphygmomanometer. Inaccurate results occur any time the needle does not rest on zero before use, necessitating a calibration.
The growing concern about the use mercury sphygmomanometer in health care rests heavily on the risk mercury poses to human health. Mercury is a hazardous material and a pollutant. Inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested.
This has led to the call by several organisations such as the World Health Organisation for the replacement of mercury-containing thermometers and blood pressure measuring devices in health care. European countries such as Sweden and The Netherlands as well as numerous hospitals in the United States have already banned its use.

The Use of Automated Digital Sphygmomanometer

Quite recently, there have been an increased use of Automated Digital Sphygmomanometer among many individuals for self-checks and also in healthcare facilities. This can be largely attributed to the ease at which the machine can be operated; requiring no prior medical skill or knowledge on the side of the user and a reduction in the level of involvement of the health professional when used in hospital settings; (1) it does not necessary require the full attention and concentration of the health worker as in the case of Mercury Sphygmomanometer and (2) it reduces the risk of ear infections and other complications usually associated with the continuous use of shared stethoscope.
However, a lot of patients and clinicians have raise concerns about the validity and accuracy of the results produced by Automated Digital Machines. Many studies have suggested the use of the Automated Digital Sphygmomanometer as a potential replacement device for blood pressure measurement, yet deviations from the standard (that is when compared to mercury sphygmomanometer) remains clinically significant.
Automated Digital Blood Pressure devices are oscillometrics, that is, they depend on the principle of oscillation as against auscultation which is seen in Mercury Sphygmomanometers. Oscillatory devices produce a digital readout and work on the principle that blood flowing through an artery between systolic and diastolic pressures causes vibrations in the arterial wall which can be detected and transduced into electrical signals.
The British Hypertension Society (BHS) and Association for the Advancement of Medical Instrumentation (AAMI) have validation criteria which Automated Digital Sphygmomanometer must satisfy before commercialisation or use. According to the AAMI, Automated Digital Sphygmomanometer must have <5 mmHg average difference and <8 mmHg standard deviation of the difference. However, Mansoor et al, (2016) concluded in their study that, Systolic readings from a previously validated device(automated digital sphgmanometer) are not reliable when used in the Emergency Room (ER) and they show a higher degree of incongruence and inaccuracy when they are used outside validation settings. Only 33% of systolic measurements and 44.5% of diastolic measurements were within the reference range in their study.
The variability is even greater, when automated blood pressure device is used in hypertensive patients. Only 24.7% of systolic measurements and 39.3% of diastolic measurements were within reference range. These findings are alarming, as in the diagnoses of hypertension, as little as 5mmHg underestimation or overestimation could have a huge impact.
McAlister and Strauss (2001) suggested that almost two-thirds of hypertensive individuals would be denied morbidity preventing treatment if the diastolic blood pressure were underestimated by 5 mm Hg and the number of persons diagnosed with hypertension would more than double if systolic blood pressure were over estimated by 5 mm Hg.
However, in non-hypertensives, Mansoor et al, (2016) found that, automated devices are capable of measuring systolic and diastolic blood pressure within the reference range when used on the right arm.
Exploring further, other studies have indicated that, the use of Automated devices can have unreliable readings when used on diabetic patients, pregnant women, elderly patients and patients with arrhythmias; and also failure to reliably detect orthostatic hypotension has also been reported.
Automated Digital Sphygmomanometer has been reported to overstate blood pressure and at times understate blood pressure. In both of these instances, it can put patient management at risk.

Conclusion and Recommendations

1.      Awareness needs to be spread amongst clinicians that there is a higher level of discrepancy when using the Automated Blood Pressure Machines on patients with certain conditions such as hypertension and Arrhythmias and also be cognizant that small systematic errors in measurement could affect a setting’s hypertension control performance.
2.      There is also the need to document the type of device used to obtain blood pressure measurements both in the clinical setting and in research.
3.      Separate protocols and criteria have to be established for the use of automated devices in different departments as the ideal conditions in which these devices are tested won’t be available when these devices are put to test on the field.
4.      Hypertensive patients, patients with arrhythmias and trauma should be monitored with manual sphygmomanometers as opposed to automated sphygmomanometers.
5.      With the call by several environmentalists and organisations such as WHO for the replacement of mercury-containing medical devices, there is an urgent need for increased research and developments of a more reliable alternative Blood Pressure machine.

Written By Assandoh De Nurse (RN, BSN-CHN; Clinical Nurse)

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