Summary

Around the world , home blood pressure monitoring (HBPM) has steadily been gaining popularity among both patients and clinicians. It is internationally recognized that HBPM is a valuable tool in the management of hypertension with evidence suggesting that HBPM measurements may have a stronger predictive power for morbidity and mortality than traditional office blood pressure readings, and can be as reliable as ambulatory monitoring. HBPM is also helpful in the management of white-coat and masked hypertension. In order for HBPM to be valid and reliable however, patients need to be educated on proper monitoring technique and require validated, correctly fitted devices. It is important therefore for clinicians to be aware of the current guidelines and recommendations regarding the proper use of HBPM.

摘要

家中血壓監察越來越普遍，被國際公認為有助處理高血壓的有效方法。証據顯示家中血壓監察與流動血壓監察有同樣的可信度，而且比傳統的診所血壓量度對高血壓並發症發病率和死亡率有更好的預測能力。家中血壓監察對處理白袍高血壓和隱性高血壓亦有幫助。為了確保家中血壓監察的有效性和可信性，病人需要學習正確的監察技巧和選用驗證過而又合適的血壓監察儀器。因此，醫生需要了解現行有關家中血壓監察的指引，以教導病人。

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Introduction

In recent times, self monitoring of blood pressure has gained popularity amongst our patients and profession, and increasingly, home blood pressure monitoring (HBPM) is being recognized as a valuable tool in the management of hypertension. A number of international agencies now include recommendations for the use of HBPM in their published guidelines including the World Health Organization – International Society of Hypertension,¹ the European Society of Hypertension (ESH) and the European Society of Cardiology,² the British Hypertension Society,³ the US National Heart, Lung, and Blood Institute (in the JNC 7 Report),⁴ the American Heart Association and the American Society of Hypertension (AHA/ASH)5 and the Japanese Hypertension Society.⁶

There are many benefits of home monitoring. HBPM allows for the measurement of blood pressure away from the clinical environment eliminating the ‘white-coat effect’, and is useful for the detection of masked hypertension.^7,8 HBPM has been shown to be reproducible and has been found to be as reliable as ambulatory blood pressure monitoring.7,8 HBPM can be a useful tool to assist the clinician in commencement and titration of antihypertensive therapy, and there is evidence that self-monitoring can be an effective adjunctive strategy in enhancing blood pressure control in hypertensive patients.⁹ Evidence is also emerging to show that self-monitoring may lead to a reduction in cardiovascular events,⁹ and that HBPM measurements are a better predictor of morbidity and mortality than traditional office blood pressure measurements.¹⁰

Although, at present, no local studies have been performed to document the prevalence and use of HBPM in Hong Kong’s primary care setting, studies in the US and Europe have estimated that up to 66% of hypertensive patients measure their own blood pressure, of whom, over half purchased and used their devices without medical advice or training.^11-13 In Asia, it has been estimated that approximately 24% of Singaporean patients, e.g., attending a government outpatient clinic used HBPM. The majority of these patients however did not monitor their blood pressure on a regular basis.¹⁴

As HBPM is often used without proper medical advice, these measurements can be inaccurate and adversely influence clinical management. Moreover, there are several devices available on the markets which have not been independently validated for clinical use. It is therefore essential that proper professional education be provided when promoting HBPM for our patients. The objective of this article is to equip primary care doctors, who are managing hypertensive patients in our community, with up-to-date knowledge on the current guidelines and recommendations for the use of HBPM.

Definitions

Diagnostic and therapeutic thresholds for hypertension on HBPM

There is already a worldwide consensus that the cut-off limits applicable for conventional office blood pressure measurements cannot be directly extrapolated to HBPM.² Many studies on both unselected and hypertensive patients have already shown that measurements taken by patients at home are often lower than readings taken in the office, and closer to the average BP recorded by 24-hour ambulatory monitors.⁵

The European Society of Hypertension (ESH) has published guidelines for the use of HBPM and recommending the use of 135/ 85 mmHg as the cutoff point for the diagnosis of hypertension on HBPM, corresponding to an office blood pressure of 140/90 mmHg.² These recommendations were based on evidence obtained from meta-analyses of published studies analyzing the relative distribution of home blood pressure and office blood pressure readings, observational studies using morbidity and mortality end-points and published clinical trials on the use of HBPM. Other agencies offer slightly varying but similar thresholds for diagnosis of hypertension on HBPM. Therapeutic thresholds for HBPM (the target home blood pressure for titration of antihypertensive therapy) however, are currently unknown, and is being explored in the ongoing HOMED-BP study.¹⁵

Although there is usually a clear correlation between an individual’s home and office blood pressures, there are a number of situations where this clearly does not occur. Therefore, when considering the relationship between home and office blood pressures, the following terminology can be used:

• True normotension
  If both office blood pressure (BP) and ambulatory or home blood pressures are normal.
• White - coat hypertension ( or isolated office hypertension)
  If office BP is persistently elevated while ambulatory or home BP is normal. White-coat hypertension is diagnosed when office BP is >= 140/90mmHg on at least 3 occasions, while 24-hour mean and daytime BPs are within their normal range or average of several home BP readings is < 135/85mmHg.
• Masked hypertension (or isolated ambulatory / home hypertension)
  This is the reverse of white-coat hypertension. In masked hypertension, individuals with normal office BP (<140/90mmHg) have elevated ambulatory or home BP values.
• Sustained or uncontrolled hypertension
  Both office BP and ambulatory or home blood pressures are elevated.

Why should we promote HBPM?

There are many reasons why HBPM is considered important. Firstly, both white-coat hypertension and masked hypertension are common. In a Japanese patient population receiving antihypertensive treatment, the prevalence of ‘white-coat’ hypertension was estimated to be 19.4% and the prevalence of masked hypertension approximately 19%.¹⁶ In Hong Kong, the prevalence of white-coat hypertension has been estimated to be approximately 28.2% of patients being managed for hypertension.¹⁷ This implies that routine clinic measurements might not be an accurate reflection of the patient’s real BP, and doctors should not rely exclusively on office measurements when making decisions regarding commencement or titration of anti-hypertensive medications.

Secondly, studies have shown that home BP measurement has a stronger predictive power for mortality and morbidity than office BP readings¹⁰ and that the presence of ‘white- coat’ hypertension and masked hypertension is of prognostic significance on cardiovascular outcomes.^18-20 In a meta-analysis on the incidence of cardiovascular events in whitecoat hypertension, masked hypertension and sustained hypertension in comparison with true normotension, seven studies involving a total of 11502 participants with an average follow-up of 8.0 years were identified. The overall adjusted hazard ratio was 1.12 for white-coat hypertension (p=0.59), 2.00 for masked hypertension (p<0.001) and 2.28 for sustained hypertension (p<0.001).²¹

Thirdly, the use of 24 hour ambulatory blood pressure monitoring (ABPM), which has traditionally been the gold-standard for the diagnosis of whitecoat hypertension and masked hypertension, is too technically demanding and costly to be performed on a routine basis. Available on the market now are several affordable, validated automatic HBPM devices which have been shown to be as reliable as ambulatory BP monitors, but easier and more acceptable for patient use.

Fourthly, a Cochrane meta-analysis of randomized controlled trials showed that patient self-monitoring was associated with a decline in systolic blood pressure (2.5 mmHg) and diastolic blood pressure (1.8 mmHg). Although this blood pressure reduction does not appear substantial in clinical terms, the conclusion of this review was that self-monitoring of home blood pressure is a useful adjunct to care and is likely to enhance compliance and lead to a reduction in cardiovascular events.⁹

How should HBPM be performed? 

The European Society of Hypertension (ESH) has provided guidelines for measurement procedures and choice of device for HBPM.²

Recommended devices

Automated self-blood pressure monitoring (SBPM) devices using oscillometric techniques with an inflatable cuff for the upper arm are recommended as they are easy to use and are not as technique-demanding as, for example, traditional auscultatory mercury-column sphygmomanometers . There are finger devices, wrist devices and upper arm automated devices available in the market. Wrist devices are particularly popular among patients as it does not require removing of clothing and are convenient. However, wrist and finger devices are not recommended as they are prone to errors because of distal site and effect of limb positions. Upper arm devices are recommended as they are the most reliable.

Device validation and calibration

Only a minority of SBPM devices available in the market have fulfilled independent validation criteria by protocols of associations, for example, the American Association for the Advancement of Medical Instrumentation, British Hypertension Society (BHS) and the EHS. The EHS has supported the establishment of a not-for-profit web site to provide updated list of validated BP-measuring devices (www.dableducational.org). Web site of BHS (www.bhsoc.org) also provides such information. 

Measurement conditions and procedures

The patient should be relaxed in the sitting position with back supported and arm supported on a table, the cuff at heart level, legs uncrossed, in a quiet room, at a comfortable temperature. BP measurement should be preceded by at least 5 minutes of rest. Patient should not talk, eat or drink in the 5 minutes before and during BP measurement. There should be no smoking or caffeine in the 30 minutes before measurement. Repeated readings should be done at one to two minute intervals. Results should be recorded either by writing or by the memory of the device. Measurements should be performed sequentially on the same arm. The arm with the higher BP should be selected.

Cuff and bladder

The length of the inflatable bladder should cover 80-100% of the arm circumference and the width should be about half that of the length. The centre of the cuff bladder should be placed at the brachial artery.

Frequency and timing of HBPM 

The EHS recommends measurements over a 7 day-schedule before each doctor visit, using morning and evening readings and performed before drugs and meals. The average of all values should be used, discarding those from the first day. There is no consensus yet whether HBPM should be done in the intervening periods. 

Special considerations in special populations

Obese people 

A conical shaped arm is common in obese people and makes it difficult to fit the cuff to the arm. This is when a wrist device may be more desirable. 

Elderly 

Elderly people have more pronounced BP variability. They may find it challenging to perform HBPM and may need the help of others. HBPM should be measured both in sitting and standing positions if postural hypotension is suspected. 

Arrhythmia 

In patients with atrial fibrillation, frequent supraventricular or ventricular extra-systoles, the stroke volume varies and makes accurate BP measurement difficult using oscillometric devices. Patients who are on beta-blockers or other anti-arrhythmic drugs can have brady-arrythmia, which also affects the accuracy of measurement. New HBPM devices with arrhythmia-detection algorithms are being developed but the diagnostic accuracy needs further evaluation. 

For patients with arrhythmia, the auscultatory method remains the preferred option, if trained. 

End-stage renal disease and diabetes 

In patients with end-stage renal disease and diabetes, the accuracy of the oscillometric devices is reduced, possibly attributable to arterial stiffness. As a result, a more aggressive BP target often needs to be set. 

Pregnancy

HBPM may help in the diagnosis of pre-eclampsia. However, only a few oscillometric BP monitors have been validated in pre-eclampsia. Moreover, there are no established thresholds in HBPM in pregnant ladies. 

Children 

The reference values and diagnostic role are uncertain. 

In whom should HBPM be performed? 

Although there is no general consensus on exactly who should undergo HBPM, many see the applicability of long term HBPM in the management of almost every hypertensive patient. Both the ESH and the AHA/ASH recommend that HBPM be used in all patients with known or suspected hypertension.^2,5 Although this would be ideal, there are some patients where the recommendation for HBPM may be emphasized more firmly. These include patients with newly diagnosed or suspected hypertension to distinguish between white-coat and sustained hypertension, patients with pre-hypertension to detect masked hypertension and those on antihypertensive treatment to evaluate the response to treatment. In addition, HBPM can be recommended to patients who require tighter blood pressure control such as those with multiple cardiovascular risk factors, features of target organ damage, diabetes or renal disease, and those with known cardiovascular disease.^{2, 5} 

Mention should be made regarding caution when recommending HBPM in certain patients who may not be ideal candidates for self monitoring. These include those in whom the HBPM measurements may result in excessive anxiety, or those who may self-modify treatment without medical consultation.²²

Conclusion

Home blood pressure monitoring has the potential to improve the quality of care and outcomes of patients with hypertension. To assist in better monitoring and management, medical practitioners should consider recommending home blood pressure monitoring to all patients, particularly those where office readings may not accurately reflect ambulatory blood pressures. In addition, home monitoring may be of use in those who require tighter control of blood pressure due to greater cardiovascular risk or poor compliance. In order to ensure optimal measurement in performing home measurements, professional advice must be provided regarding the choice of device and proper technique.

Key messages

1. Home blood pressure monitoring (HBPM) is a valuable tool in the management of hypertension, especially for those patients with high cardiovascular risks requiring tighter blood pressure control.
2. HBPM is useful for the diagnosis of ‘white-coat hypertension’ and ‘masked hypertension’.
3. HBPM can be as reliable and valid as ambulatory blood pressure monitoring.
4. Patients should perform HBPM using validated, automatic, oscillometric devices and doctors need to be aware of the proper measurement techniques and procedures so that they can better educate their patients regarding its correct use.

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References