High blood pressure (BP) is the leading modifiable risk factor for death and disability in the world, affecting an estimated 1.4 billion adults globally, and leading to over 10 million deaths per year [1,2]. It is a leading cause of heart disease, stroke, and chronic kidney disease and a major contributor to escalating healthcare costs . With an overall global adult prevalence of 31%, high BP is highly prevalent in all major regions of the world . However, in absolute numbers, it is low-to-middle income countries (LMICs) that bear the highest burden of illness, having over one billion individuals affected, and possessing awareness, treatment and control proportions that lag high-income countries to a considerable degree . Accordingly, ongoing efforts to improve the diagnosis, prevention, treatment, and control of hypertension globally must include tailored interventions that prioritize reductions in regional disparities .
Accurate and reliable BP measurement is essential for the proper diagnosis and management of hypertension . On a population-wide level, a 5-mmHg difference in SBP corresponds to an estimated 6% absolute and 30% relative change in hypertension prevalence . Accordingly, the effect of a 5-mmHg error in BP measurement, assuming a global prevalence of 1.4 billion , could lead to the incorrect classification of hypertension status in 84 million individuals worldwide. Therefore, the ramifications of inaccurate measurement on a global level are profound.
Blood pressure is a physiological parameter that changes constantly in response to endogenous factors and exogenous stimuli . This variability makes assessment of ‘usual’ BP, which is defined as an individual's true or genuine BP, challenging. BP measurement is perhaps the most commonly performed procedure in clinical medicine and, although, at first glance, it seems simple, in reality, many steps must be performed sequentially and optimally in order to produce a reproducible result reflective of usual BP. Accordingly, the individual responsible for measuring BP, herein referred to as the ‘observer’, must be meticulous in terms of following recommended techniques . The challenges posed by the variable nature of BP were recognized over a century ago by Riva-Rocci et al., who noted that taking multiple measurements and standardizing the measurement conditions could optimize use of the technique in clinical practice. He concludes, in his seminal paper written in 1896, that ‘… if the procedures are neglected, and the doctor is satisfied with a crude reading, the method will become useless and will be quickly abandoned as a scientists’ indulgence’ .
Unfortunately, in contemporary clinical practice, BP measurement is often suboptimally performed, and this type of unstandardized BP measurement leads to errors that can inappropriately alter management decisions in 20–45% of cases [10–13]. The problem of unstandardized BP measurement has persisted for decades despite extensive education and substantial efforts to raise awareness on the adverse consequences of inaccurate clinic BP measurement [5,14]. Time constraints and suboptimal technique leading to poorly performed auscultation are responsible for much of this error [10,15]. Potential solutions to minimize error, discussed below, include simplifying the measurement process by using automated devices and encouraging observers to undergo certified training and re-training to promote ongoing use of standardized measurement techniques.
The aim of the Lancet Commission on Hypertension was to identify key actions to improve the global management of BP both at the population and the individual levels, and to generate a campaign to adopt the suggested actions at national levels to reduce the impact of elevated BP globally . The purpose of this position statement is to provide guidance towards optimizing observer-related clinic BP measurement performance for hypertension diagnosis and treatment, with special attention given to measurement in LMIC settings. We begin with a brief review of different measurement modalities, including a discussion of optimal measurement technique and the errors that result from deviating from standardized measurement practices. We then outline the impact of observer training on performance of BP measurement. Subsequently, we discuss BP measurement in LMIC settings, specifically the practical considerations that limit achievement of best practice. We close with recommendations for optimizing observer accuracy in clinic BP measurement and provide suggestions on future directions.
TYPES OF BLOOD PRESSURE MEASUREMENT USED IN CLINICAL PRACTICE AND OPTIMAL MEASUREMENT TECHNIQUE
Direct (or intra-arterial) and indirect (cuff-based) BP measurement are the two major methods employed in the clinical care setting and are summarized in Table 1. Indirect measurement is typically performed via auscultation or by using a semi-automated or fully automated device, which most often uses the oscillometric technique (Table 1). Although there are definitions in the literature for semi-automated and automated BP measurements, herein we refer to semi-automated as those devices that require a manual inflation (e.g. with using bulb compressions). Once inflation has been completed, these devices typically use an automated deflation process to determine BP. In contrast, fully automated devices have automated inflation and deflation – the user initiates a measurement, usually by pressing a button, and the remainder of the inflation–deflation process is automated. Automated office BP (AOBP) measurement is a subtype of automated measurement that involves taking sequential automated measurements rather than a single measurement at a time. In the oscillometric technique, arterial pulses are first sensed, filtered, processed and, then, a proprietary algorithm is applied to estimate BP .
BP measurement should be performed carefully by a trained observer using standardized methodology (Table 2 and Fig. 1; Supplementary Figures S1–S5, https://links.lww.com/HJH/B93) . The mean of multiple research quality auscultatory and, more recently, automated oscillometric measurements, sometimes taken over two or more clinical visits, was the method used to estimate the usual BP in many foundational prognostic and therapeutic studies in the field of hypertension [17–19]. Multiple readings over time are required to estimate the usual BP, allow for regression to the mean, and reduce the white-coat effect .
CAUSES OF INACCURATE BLOOD PRESSURE MEASUREMENT IN CLINICAL PRACTICE
Unfortunately, standardized auscultatory measurement is not performed commonly in clinical practice [12,21]. It is also rarely performed by medical trainees [11,22]. Instead, ‘casual’ measurement, in which standardized methodology is not followed, is common. Casual measurement typically leads to higher variability, overestimation of SBP by 5–10 mmHg, and poorer correlation with hypertension related end-organ damage [10,11,15,23].
Multiple causes of inaccuracy exist and can be categorized into patient-related, procedure-related, equipment-related, or observer-related (Table 3) . Poorly performed auscultation is responsible for much of the error [10,15]. Major barriers to standardized BP measurement include insufficient attention paid to optimal technique, lack of observer education, competing demands and observer time constraints, and use of inaccurate equipment [8,14,25]. Common observer-related errors in the clinical setting include failure to include a 5-min rest period, talking during the measurement procedure, using an incorrect cuff size, and failure to take multiple or bilateral measurements [12,23]. Time constraints are a particularly common reason for casual measurements, as a casual reading takes about 2 min to perform versus 8 min for a standardized measurement [12,26]. Physician readings are higher than nurse readings, which has been attributed to incremental white-coat effect . Ultimately, the observer is responsible for performing a proper measurement and ensuring to the greatest extent possible that all of the potential causes of inaccuracy are avoided.
ADVANTAGES OF AUTOMATED BLOOD PRESSURE MEASUREMENT
Use of automated BP measurement is also supported by many foundational prognostic and therapeutic studies in the field of hypertension [17–19]. Its major advantage is that it reduces observer error by automating the BP measurement process. Accordingly, less observer expertise is needed, auscultatory training is not required, and the observer can focus on mastering a smaller number of essential aspects of BP measurement . Automated BP could improve BP measurement technique even further if devices programmed to take BP in a guideline-concordant fashion were available. Examples include electronically displayed step-by-step instructions to remind observers of proper technique and auto-controlled initiation sequences that require a timed rest period before the first reading is performed.
An additional, and critically important advantage of automated BP, although beyond the immediate focus of this position paper, is that it enables many measurements to be taken in the out-of-clinic setting in the usual environment of each individual. Out-of-clinic measurement includes 24-h ambulatory monitoring and home BP monitoring and leads to much better assessment of usual BP because, in addition to eliminating observer error, it eliminates white-coat (high clinic but normal out-of-office BP) and detects masked hypertension (normal clinic but high out-of-office BP) phenomena. Indeed because of the existence of white-coat, and masked hypertension effect, which affect 9–24 and 9–17% of untreated and treated individuals, respectively, even meticulously performed standardized office BP may not be representative of usual BP . Contemporary guidelines recommend confirming the diagnosis of hypertension with out-of-office BP measurements and treating masked, but not white-coat, hypertension .
Twenty-four-hour ambulatory and home BP monitoring are far superior to clinic measurements in terms of their ability to predict cardiovascular events [31,32]. 24-h BP monitoring is the gold standard for diagnosing hypertension and home BP monitoring is ideal for performing long-term follow-up monitoring of treated hypertensive patients, especially when coupled with nurse or pharmacist case management [33–36]. If resources allow, use of both of these measurement methods is highly recommended [30,35,37,38]. Both out-of-clinic measurement modalities require proper technique, and healthcare professionals must understand that home BP monitoring requires patient training in order to be effective in improving clinical decisions [33,36,39].
As mentioned above, AOBP offers the ability to perform three to five unattended, sequential BP measurements and auto-calculate the mean . AOBP is a subtype of fully automated BP measurement; the critical distinction is that sequential readings are automated. Practically, this means the observer is required to initiate only the first reading of the sequence; she or he can then leave and return when the entire sequence is finished (as opposed to remaining in the room to initiate each sequential measurement). Use of AOBP, particularly when performed when the patient is alone in the room, facilitates a more standardized measurement process (e.g. no talking, multiple automated measurements taken sequentially). Consequently, the AOBP technique is associated with reduced white-coat effect [40,41,42–44]. AOBP requires additional space and time and the cost of AOBP devices is also 5-fold to 10-fold higher than regular automated (home) devices, which also limits use in the LMIC setting. However, if these barriers are not present, use of AOBP should be considered to enable greater standardization of in-clinic BP measurements.
Some automated devices have been specifically designed for use in the LMIC setting [45–47].
AUTOMATED DEVICE ACCURACY
An important issue with automated devices is that many have not been clinically validated for measurement accuracy . Clinical validation involves demonstrating that the device meets the accuracy requirements of international BP measurement standards . This process involves performing a protocol-based comparison using multiple measurements against a blinded, two-observer auscultatory reference standard. To maximize accuracy, only validated devices should be used in clinical practice .
In some individuals, even validated devices may produce BP measurements that differ substantially from auscultation; this may result from variations in algorithm performance and/or arterial wall properties [51,52]. For this reason, it is desirable to ensure that a specific device is performing well in a specific patient. Unfortunately, there is no consensus on how to do this in an efficient and feasible manner that is applicable in clinical practice. This issue is discussed in further detail elsewhere [53,54].
OBSERVER TRAINING TO IMPROVE CLINIC BLOOD PRESSURE MEASUREMENT
Observer training has been proposed as a solution to poor measurement technique. Training programs leading to short-term success in improving measurement technique have been described, all emphasizing the fundamentals of proper BP measurement (Table 2), and varying in their delivery format, from web-based to in-person, and in length, from 30 min to full-day sessions [55–57]. Clearly, shorter, web-based programs are preferred because of their practical advantages, lower cost and scalability. Beyond observer training alone, bundled quality improvement programs that combine use of automated office BP measurement with provider education on proper measurement and advice on clinical workflow improvement have been examined and shown to increase use of automated measurement and reduce terminal digit preference . Additional approaches that have been proposed include training patients to recognize when their care providers are performing improper measurement and having regulatory agencies enforce use of standardized measurement, but the practical implementability of these propositions is uncertain [59,60].
A trained nurse with auscultatory expertise can approximate daytime ambulatory BP, a commonly used reference standard, better than automated devices . However, the generalizability of this finding to an observer with less expertise undergoing a single training seminar, in the LMIC setting or otherwise, is likely to be low. Auscultation appears to be particularly difficult to perform in a uniform manner over time. The inter-observer variability of auscultatory BP measurements between expert observers was minimized by repeated training sessions, validating the importance of retraining . However, following each training session, between-observer variability increased after just 1–2 months, indicating that very frequent re-training is required to maintain auscultatory skills. These data indicate that training requirements are greater over the short-term and long-term if the auscultatory technique is used, which is not feasible for widespread implementation, particularly in the LMIC setting. Accordingly, use of automated devices is recommended to minimize additional training requirements.
Overall, training improves BP measurement practices over the short term and retraining is required to maintain skills over the long term. The optimal frequency of retraining is unclear. As a practical compromise, to avoid a burdensome retraining schedule yet ensure relatively frequent refreshment of skills, retraining is recommended at least annually.
ADDITIONAL CHALLENGES TO OPTIMIZING CLINIC BLOOD PRESSURE MEASUREMENT IN THE LOW-TO-MIDDLE-INCOME SETTING
Additional challenges exist in LMIC settings and many are not easily solved. These are summarized in Table 4, together with proposed solutions.
RECOMMENDATIONS FOR OPTIMIZING OBSERVER PERFORMANCE IN BLOOD PRESSURE MEASUREMENT AND FOR STAKEHOLDER IMPLEMENTATION
Recommendations for optimizing observer performance in BP measurement and stakeholder implementation are listed in Fig. 2 and focus on performing simplified, standardized measurements using validated semi-automated or automated devices in a properly configured setting, and ensuring proper observer training and periodic retraining. Task-sharing by training nonphysician healthcare or lay providers, such as nurses and community health workers to perform measurement, is strongly advised because it frees physicians, who are in short supply relative to other healthcare providers, to perform other work and also reduces white-coat effect [27,63,64]. Task shifting alone may not improve BP control if clinics are overburdened, equipment is unreliable, or antihypertensive therapy is unavailable . The core curricula of healthcare professional schools and postgraduate training programs should include standardized training and performance testing in blood pressure measurement.
Given the importance of proper observer training, programs are needed to assist observers in acquiring the necessary skills to perform proper BP measurement. To this end, training courses that provide certification in standardized measurement, endorsed by prominent national and international organizations working in the field, would encourage and substantiate best measurement practices. The World Hypertension League has developed resources to assist providers to perform BP screening . Proper BP measurement Certification programs should not be onerous and need to be simple, brief, multilingual, low-cost (ideally, free), easily repeatable and widely accessible. Research is needed to identify the best methods of delivering training, and further work is required to identify how and where training and certification could be best performed and if certification should be required.
Given the enormous, and increasing, global burden of hypertension, the need to improve all aspects of prevention, detection, treatment and control is clear . The importance of proper BP measurement to optimal hypertension diagnosis and management cannot be overemphasized. Much of the error in BP measurement is within the control of the observer. Therefore, simplifying, standardizing, and automating measurement practices and ensuring proper observer education, training and certification is needed. Even these relatively straightforward recommendations can be challenging to implement, but they have the potential to markedly improve detection and management of hypertension across the world. Given the importance of accurate BP assessment, and the lack of impact of previous efforts to train healthcare workers, consideration should be given to regular certification in BP assessment.
This position statement is supported by the World Hypertension League, Artery Society, American Medical Association, American Heart Association, Hypertension Canada, Resolve to Save Lives, European Society of Hypertension Working Group on Blood Pressure Monitoring and Cardiovascular Variability.
Conflicts of interest
R.P. is a co-founder of a blood pressure measurement start-up company, mmHg Inc. No products are currently in the market. N.R.C.C. was a paid consultant to the Novartis Foundation (2016–2017) to support their program to improve hypertension control in low-to-middle-income countries, which includes travel support for site visits and a contract to develop a survey. N.R.C.C. has provided paid consultative advice on accurate blood pressure assessment to Midway Corporation (2017). M.K.R. is Vice President, Improving Health Outcomes at American Medical Association. G.W. is Director, Outcomes Analytics at American Medical Association. The remaining authors have no disclosures. G.S. is Chairman of European Society of Hypertension Working Group on BP Monitoring, ISO Sphygmomanometer committee member, and has conducted validation studies for various manufacturers of BP-measuring technologies and advised manufacturers on device and software development. J.K.C. is immediate past President of the Artery Society. A.E.S. received speaker fees from Novartis and Omron for scientific lectures on blood pressure and CV risk assessment, and Servier for presenting on raising awareness of blood pressure measurement. She a paid consultant to Abbott Pharmaceuticals on antihypertensive medication, and is President of the International Society of Hypertension.
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