The Effects of Acupuncture on Hypertension: A Systematic Literature Review

Abstract

Background: Hypertension is a significant problem in the UK: 12.5 million people, more than 1 in every 4 adults, are affected. The costs of medications to manage hypertension in the UK may be in excess of £1 billion per annum. Alternative approaches to managing hypertension are therefore important to consider. Acupuncture has been identified as one such approach.

Aims: The aim of this systematic review was to retrieve, critically analyse and synthesise the existing research literature to determine the effects of acupuncture on hypertension. The findings of the review were used to inform recommendations on the use of acupuncture for hypertension in clinical practice, and also recommendations for future research on the topic.

Methods: Systematic searches on electronic databases were undertaken. The searches focused on randomised controlled trials testing the effects of acupuncture on hypertension. From the 102 relevant studies identified in the searches, six trials were selected for inclusion.

Findings: The trials selected for inclusion in this review were inconclusive about whether acupuncture, in comparison to sham acupuncture, is effective at reducing blood pressure in people with hypertension. It was concluded that acupuncture may, but will not necessarily, have a positive effect on hypertension. It was also concluded that acupuncture is unlikely to cause harm to those who choose to use it. However, there were multiple significant limitations to the trials selected for inclusion in this review. Subsequently, these trials do not provide high-quality evidence to inform clinical practice in relation to the use of acupuncture for hypertension.

Conclusions: Nurses may recommend, provide education on and (where they are trained and qualified to do so) administer acupuncture to patients with hypertension who choose to use acupuncture. Nurses should ensure patients understand that although acupuncture may not have an effect on their hypertension, it is unlikely to cause them harm. Additional research on acupuncture for hypertension is essential to further informing evidence-based practice.

Contents

• Abstract
• 1.0 Introduction, Background and Rationale
• 2.0 Methods
• 3.0 Findings and Critical Review
• 4.0 Discussion
• 5.0 Conclusion and Recommendations
• References
• Appendices

1.0 Introduction, Background and Rationale

This paper presents a systematic review about the effects of acupuncture on hypertension. Chapter 1 begins by providing an overview of hypertension and acupuncture, and the rationale for and aims of the review. Chapter 2 then outlines the review methodology, and justifies this with reference to the literature. Chapter 3 presets the findings of the review, and a critical discussion of the literature on which these findings are based. Chapter 4 discusses the findings in relation to the broader literature, and also considers their application to practice. Chapter 5 concludes with a summary of the review and recommendations for practice and research.

1.1 Hypertension

‘Hypertension’ is the clinical term for high blood pressure (Bradley, 2015). In the United Kingdom (UK), hypertension is diagnosed when a person’s persistent systolic blood pressure is ≥140mmHg and/or their persistent diastolic blood pressure is ≥90mmHg (National Institute for Health and Care Excellence [NICE], 2011). Hypertension is also diagnosed when a person must take anti-hypertensive medication/s to maintain a ‘normal’ blood pressure (Bradley, 2015).

The pathophysiology of hypertension is complex. In a small number of cases there is a clear physiological cause, but in perhaps up to 95.0% of cases the cause is undetermined and idiopathic (Chen, 2012). Hypertension is known to result when the body’s processes for blood pressure regulation – including the renin-angiotensin-aldosterone system (RAAS) – become chronically disordered (Chen, 2012). However, the reason/s why these processes become disordered, and why they remain so instead of returning to homeostasis, is frequently unclear (Chen, 2012). Increasingly, it is understood that hypertension has epigenetic and environmental causes (e.g. dietary intake, physical activity, obesity, etc.) (Chen, 2012; Bradley, 2015). Hypertension is also recognised to be strongly correlated with increasing age (Bradley, 2015).

Hypertension is problematic because it significantly increases a person’s risk of developing cardiovascular disease. This risk occurs because hypertension places the heart and vasculature under chronic excessive strain (Bradley, 2015). For a person with moderate hypertension, the risk of cardiovascular-related mortality is at least 1.31 times greater than for a person without hypertension (Wu et al., 2015). For each 10mmHg by which a hypertensive person’s blood pressure is reduced, their overall risk of experiencing a harmful cardiovascular event (e.g. a myocardial infarct, a stroke, heart failure, etc.) decreases by 20.0% (Ettehad et al., 2016).

For this reason, treating hypertension is a priority identified in UK clinical guidelines (NICE, 2011). These guidelines recommend that all people in the UK diagnosed with hypertension are prescribed one or more suitable anti-hypertensive medications (NICE, 2011). Anti-hypertensive medications are divided into two broad classes: those which block the RAAS and induce vasodilation, and those which promote water and sodium excretion and reduce the intravascular blood volume (Jackson & Bellamy, 2015). Vasodilation and reduced intravascular volume, alone or in combination, are essential in achieving and maintaining reductions in blood pressure.

Research shows that ant-hypertensive medications are highly effective at managing hypertension. Indeed, they result in average reductions in blood pressure of 13.6mmHg (systolic, for single medications) to 17.3mmHg (systolic, for combination medications) (Bronsert et al., 2013). Nevertheless, hypertension remains a significant problem in the UK – indeed, Public Health England (2017) estimates that 12.5 million people in the UK, more than 1 in every 4 adults, have hypertension. The costs of medications to manage hypertension in the UK may be in excess of £1 billion per annum (NICE, 2011). For these reasons, alternative approaches to managing hypertension are important to consider. Acupuncture is one such approach.

1.2 Acupuncture

Acupuncture is a Traditional Chinese Medicine (TCM) therapy which has been practiced in China for more than 2500 years (Chang, 2012). It is based on the belief that essential energy, or qi, travels throughout the human body on pathways, or meridians (Chang et al., 2012; Kawakita & Okada, 2014). Turbulence or blockages in the flow of qi along the meridians results in the symptoms of a disorder (Kawakita & Okada, 2014) – for example: hypertension. Acupuncture involves placing fine metal needles at pre-determined points along a meridian, with the aim of rebalancing the qi, and subsequently relieving the symptoms of the disorder and restoring the person to a state of wellbeing (Kawakita & Okada, 2014). In relation to hypertension, it is believed that acupuncture helps to control the body’s processes for blood pressure regulation – including the RAAS – though its mechanism of action is still largely unclear (Li et al., 2019).

It is important to note that there is a recent Cochrane systematic review on the effects of acupuncture on hypertension (Yang et al., 2018). The Cochrane Collaboration is recognised to produce systematic reviews which are methodologically sound, and so provide high-quality evidence to inform clinical practice (LoBiondo-Wood & Haber, 2014). However, there are a number of limitations with Yang et al.’s (2018) review. In particular, the review considered the effects of acupuncture alone and in combination with other interventions, and it compared acupuncture with sham acupuncture, no treatment and anti-hypertensive medications (Yang et al., 2018). Because so many variables were considered, Yang et al. (2018) were unable to develop a firm conclusion about whether acupuncture was effective at reducing blood pressure in people with hypertension. This is a limitation this systematic review aims to address. 

1.3 Aim of the Review

The aim of this systematic review is to retrieve, critically analyse and synthesise the existing research literature to determine the effects of acupuncture on hypertension. The studies selected for inclusion in this review will be carefully considered to avoid the methodological limitations of the existing Cochrane systematic review on the topic, noted above. The findings of the review will be used to inform evidence-based recommendations on the use of acupuncture for hypertension in clinical practice, and also recommendations for future research on the topic.

2.0 Methods

To gather evidence to inform practice in relation to the use of acupuncture to manage hypertension, a systematic review was undertaken. As with all other types of literature reviews, the purpose of a systematic review is to retrieve, critically appraise, synthesise and summarise the current, quality published research on a topic of interest (Macnee & McCabe, 2008). This is done with the aim of developing evidence to inform clinical practice in relation to the topic.

Systematic reviews form the basis of evidence-based practice (Macnee & McCabe, 2008). This is the “conscientious and judicious” use of current, quality research to guide practice (Titler et al., 2019: p.3). Evidence-based practice is important: research consistently shows that it decreases variability in practice and, subsequently, improves patient outcomes (Emparanza et al., 2015; Black et al., 2015). Therefore, the Nursing and Midwifery Council’s (2018: p.9) Code requires all nurses in the UK to “always practice in line with the best available evidence”.

Systematic reviews differ from other types of literature reviews because the methods used to retrieve, critically appraise, synthesise and summarise the studies is detailed and repeatable (Webb & Roe, 2007). Systematic reviews aim to gather all the available primary research on the topic, and therefore require methods which are carefully designed and implemented (Clarke, 2011). The methods used for this review are presented and justified in the following sections.

2.1 Research Question

Grove et al. (2013) recommend that all literature reviews are based on a well-developed research question, to focus the searches and the evidence retrieved. There are a number of different frameworks which can be used to develop clear, answerable research questions (Grove et al., 2013). The question for this review was developed using the population-intervention-comparator-outcome (PICO) framework. This is the most common framework for developing research questions for reviews involving quantitative studies (Houser, 2018).

The PICO framework completed for this review is shown in Appendix 1. The population (P) was adults with confirmed hypertension, the intervention (I) was needle acupuncture, the comparator (C) was sham acupuncture, and the outcome (O) was change in systolic and/or diastolic blood pressure. This gave the research question: ‘In patients with hypertension, is acupuncture, in comparison to sham acupuncture, effective at reducing systolic and/or diastolic blood pressure?’

2.2 Electronic Databases

Electronic databases are the “major sources of information” for literature reviews (Coughlan & Cronin, 2017: p.56), and so the searches for this review focused on these databases. Five databases were searched: the British Nursing Index (BNI), the Cumulative Index of Nursing and Allied Health Literature (CINAHL), Excerpta Medica Online (EMBASE), Medical Literature Online (MEDLINE) and the Web of Science. These are identified as the key electronic databases to access studies related to nursing and broader health topics (Moule et al., 2017).

In addition to electronic database searches, manual searches were also completed. This involved ‘back-chaining’, or searching the reference lists of selected studies to identify other potentially-relevant studies (Tappen, 2011). Back-chaining improves the comprehensiveness of the searches undertaken, and increase the number of studies retrieved (Holland & Rees, 2010).

2.3 Search Terms

As recommended by Aveyard (2014), the terms used to search the databases were developed from the research question. The key words in the research question – including hypertension and acupuncture – and their synonyms were used. A full list of terms is provided in Appendix 2. 

Where relevant, the search terms were truncated with an asterisk; this ensured the searches captured words with variable endings and spellings (Courtney & McCutcheon, 2010). For example: searching with the term hypertens* retrieved studies containing hypertension and hypertensive. Groups of keywords were also placed in parentheses; this ensured the searches captured entire terms rather than each word separately (Dieterle & Hooper-Lane, 2014). For example: searching with the term “blood pressure” retrieved studies containing the full term.

The search terms were combined into strings using the Boolean operators AND and OR. The operator AND was used to narrow the searches, by returning studies containing all the specified search terms (Bettany-Saltikov, 2012) – for example: hypertens* AND acupuncture. The operator OR was used to expand the searches, by returning studies containing any of the specified search terms (Bettany-Saltikov, 2012) – for example: hypertens* OR “blood pressure”

2.4 Limiters and Inclusion/Exclusion Criteria

Detailed criteria were used to determine the types of studies which would be included in, and excluded from, the review (Coughlan et al., 2013). These are listed in Appendix 3. There was no scope in this review for translation, and so only studies published in or translated into English were considered. Although the most current literature – and, so, that most relevant to the current clinical context – is published within the past 10 years (Burns & Grove, 2011), for this review the date range was extended to 15 years to capture a number of important older studies.

Only studies published in peer-reviewed journals were considered, as these have been confirmed by other experts in the field as being of acceptable methodological quality (Courtney & McCutcheon, 2010). Only studies involving human subjects were considered, as the effects of acupuncture in animals can be variable (Habacher et al., 2006). Only studies available in full-text were considered, to ensure there was sufficient data for extraction and quality appraisal.

Only randomised controlled trials were considered. These involve research participants being randomly allocated to an ‘intervention group’ or a ‘control group’ (Nelson et al., 2015). Therefore, differences between people – for example: age, ethnicity, gender, baseline BP, history of anti-hypertensive medication use, etc. – are equally distributed between the groups, and this minimises confounding and bias (Nelson et al., 2015). Subsequently, randomised controlled trials are the primary research methodology which produces the highest quality of evidence to inform clinical practice (Oxford Centre for Evidence-Based Medicine, 2009).

Finally, only randomised controlled trials which compared acupuncture (the ‘intervention’) and sham acupuncture (the ‘control’) were considered. There were a number of randomised controlled trials identified which compared acupuncture with ‘treatment-as-usual’ (Chen et al., 2013; Liu et al., 2015), and with various anti-hypertensive medications (Chen et al., 2006; Chen et al., 2010; Shen & Shi, 2010; Zhang et al., 2012). However, these were excluded because they did not relate directly relate to the question about the effectiveness of acupuncture.

Where possible, the inclusion and exclusion criteria were applied as ‘limiters’ on the databases (e.g. for publication date, publication language and full-text). Otherwise, the criteria were applied during the process of screening the literature. This process is outlined in the following section.

2.5 Summary of Study Selection

As shown in Appendix 4, the searches on the electronic databases returned 102 studies (excluding duplicates). As recommended by Aveyard (2014), these studies were screened for inclusion at two stages. Firstly, the title and abstract of all the studies were read; this resulted in the exclusion of 87 studies. The remaining 15 studies were read in full-text. This resulted in the exclusion of an additional 9 studies, because they were not randomised controlled trials (n=4), or because they were studies which did not include a sham acupuncture ‘control’ group (n=3), were not published in a peer-reviewed journal (n=1) or were not available in full-text (n=1).

The remaining six studies were selected for inclusion in this review (Macklin et al., 2006; Flachskampf et al., 2007; Yin et al., 2007; Kim et al., 2012; Zheng et al., 2016; Zheng et al., 2018). The process of selecting these studies is illustrated in a PRISMA diagram (Moher et al., 2009), in Appendix 5. An overview of the selected studies is presented in Appendix 6.

2.6 Data Extraction and Analysis

A tool was developed to guide the extraction of data from the studies (Polit & Beck, 2010). Data extraction is the essential process of reading and re-reading each study, to identify data to enable its quality appraisal and to answer the research question (Bettany-Saltikov, 2012). The data extraction tool used for this review is provided, completed, in Appendices 6 and 7. To ensure the tool was efficient and accurate, it was piloted on a number of the studies excluded during the full-text screening, and refined, prior to being used for the final data extraction.

2.7 Quality Appraisal and Data Analysis

Each of the six studies selected for the review were critically appraised. This involves a process of determining the methodological quality of the study (LoBiondo-Wood et al., 2019) and, therefore, its value in answering the research question. There are a variety of frameworks which can be used to guide critical appraisal (Moule & Goodman, 2009); however, the framework used for this review was that developed by the Critical Skills Appraisal Programme for randomised controlled trials (CASP, 2018). The completed critical appraisal is presented in Appendix 8.

The data from the studies was analysed using two broad processes. Quantitative analysis was undertaken, where relevant – for example: the pre- and post-intervention systolic and diastolic blood pressures from the participants in each study were pooled and averaged. Qualitative analysis was also undertaken, where relevant – for example, information relating to the effects of acupuncture on hypertension was organised into similar ‘themes’, or ideas, for reporting.  

3.0 Findings and Critical Review

3.1 General Characteristics of the Selected Studies

3.1.1 Trial Location and Participants

As noted, six randomised controlled trials were selected for inclusion in this systematic review (Macklin et al., 2006; Flachskampf et al., 2007; Yin et al., 2007; Kim et al., 2012; Zheng et al., 2016; Zheng et al., 2018). These studies were conducted in the United States (Macklin et al., 2006), Germany (Flachskampf et al., 2007), South Korea (Yin et al., 2007; Kim et al., 2012) and China (Zheng et al., 2016; Zheng et al., 2018). The studies included an average of 147 participants, ranging from 30 patients (Zheng et al., 2016) to 428 patients (Zheng et al., 2018).

3.1.2 Trial Definition of Hypertension

Each of the trials included participants with diagnosed hypertension. In most of the trials (n=5, 83.3%), hypertension was diagnosed when a patient’s systolic blood pressure was ≥140mmHg, and/or their diastolic blood pressure was ≥90mmHg (Macklin et al., 2006; Flachskampf et al., 2007; Kim et al., 2012; Zheng et al., 2016; Zheng et al., 2018). Half of the trials (n=3, 50.0%) also specified an upper ‘acceptable’ limit on the systolic and diastolic blood pressure (Macklin et al., 2006; Kim et al., 2012; Zheng et al., 2018), perhaps to ensure the participants’ safety. It is important to note that one study also included patients with pre-hypertension: a systolic blood pressure of ≥120mmHg and/or a diastolic blood pressure of ≥89mmHg (Yin et al., 2007).

Half of the trials (n=3, 50.0%) only included patients with essential hypertension (Yin et al., 2007; Zheng et al., 2016; Zheng et al., 2018). ‘Essential hypertension’ is hypertension due to an undetermined, idiopathic cause (Bolivar et al., 2013). The other three trials also included people with secondary hypertension (Macklin et al., 2006; Flachskampf et al., 2007; Kim et al., 2012).

All six of the studies selected for inclusion reported participants’ average baseline systolic and diastolic blood pressures. Across all the trials, the average baseline systolic blood pressure for patients in the intervention group was 140.6mmHg, ranging from 131.0mmHg (Flachskampf et al., 2007) to 149.6mmHg (Macklin et al., 2006). The average baseline diastolic blood pressure for patients in the intervention group was 88.9mmHg, ranging from 81.0mmHg (Flachskampf et al., 2007) to 94.1mmHg (Kim et al., 2012). None of the studies reported significant differences in the baseline blood pressures between patients in the intervention and the control groups.

3.1.3 Trial Acupuncture Protocols

The studies tested the effects a variety of different types of acupuncture on hypertension. Two-thirds of the trials (n=4, 66.7%) tested traditional Chinese acupuncture, though Kim et al. (2012) tested traditional Korean acupuncture and Yin et al. (2007) tested modern Korean acupuncture. The studies involved accessing a variety of acupoints – from a single acupoint (Zheng et al., 2016: acupoint LR3) to up to thirty-two acupoints (Macklin et al., 2006: acupoints not specified). In half of the trials (n=3, 50.0%) of the trials, individualised acupoints were selected for a patient after a diagnosis considering their unique physiology, underlying diagnoses and/or current physical wellbeing (Macklin et al., 2006; Flachskampf et al., 2007; Yin Zheng et al., 2018).

The trials used a variety of different acupuncture protocols. The intervention period, throughout which patients received acupuncture, ranged from 2 weeks (Zheng et al., 2016) to 8 weeks (Macklin et al., 2006; Yin et al., 2007; Kim et al., 2012). In the intervention period, patients received between 10 acupuncture sessions (Zheng et al., 2016: 5 sessions per week) and 22 acupuncture sessions (Flachskampf et al., 2007: 3 to 4 sessions per week). In most of the trials (n=5, 83.3%), the acupuncture sessions were 30 minutes’ duration (Macklin et al., 2006; Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2016; Zheng et al., 2018), though in Kim et al.’s (2012) trial the acupuncture sessions were limited to 20 minutes’ duration. The participants were followed-up for an average of 19.3 weeks, ranging from 8 weeks (Yin et al., 2007; Kim et al., 2012: no follow-up beyond trial period) and 12 months (Zheng et al., 2016).

3.2 Findings – Effects of Acupuncture on Hypertension

Overall, there was a lack of consensus among the studies about whether acupuncture, in comparison to sham acupuncture, is effective at reducing systolic and/or diastolic blood pressure. Some of the trials selected for inclusion suggested acupuncture is more effective than sham acupuncture. Others suggested it might be more effective, and another found that it was not more effective. These findings are outlined in greater detail in the following section:

3.2.1 Acupuncture IS Effective at Reducing Hypertension

Half of the studies (n=3, 50.0%) concluded that active acupuncture is more effective than sham acupuncture for reducing blood pressure in people with hypertension. For example: in the trial conducted by Flachskampf et al. (2007), there was a mean reduction in participants’ blood pressure of 6.4mmHg (systolic) and 3.7mmHg (diastolic), while there was no reduction in the sham acupuncture group (p<0.001). In Yin et al.’s (2007) trial, the mean blood pressure for the group receiving acupuncture decreased from 136.8/83.7mmHg to 122.1/76.8mmHg, while again there was no change in the mean blood pressure for the control group (p<0.01). Similarly, in Zheng et al.’s (2018) trial, acupuncture resulted in an average decrease in participants’ overall blood pressure of 3.3mmHg, which was significant in comparison to the control group.

3.2.2 Acupuncture MAY BE Effective at Reducing Hypertension

One third of the studies (n=2, 33.3%) concluded that active acupuncture may be more effective than sham acupuncture for reducing blood pressure in people with hypertension. For example: the trial conducted by Kim et al. (2012) found that there were no significant changes in the blood pressure of patients receiving acupuncture except in relation to nighttime diastolic blood pressure, where there was a decrease of 2.5mmHg (p=0.041). Similarly, in Zheng et al.’s (2016) trial, the only significant change in the blood pressure of patients receiving acupuncture was in relation to systolic blood pressure, where there was a decrease of 5.2mmHg (p=0.006).

3.2.3 Acupuncture IS NOT Effective at Reducing Hypertension

The final study (n=1, 16.7%) concluded that active acupuncture was not more effective than sham acupuncture for reducing blood pressure in people with hypertension. This trial found that active and sham acupuncture resulted in similar reductions in systolic blood pressure (Macklin et al., 2006). In relation to diastolic blood pressure, however, sham acupuncture resulted in a slightly greater reduction in blood pressure than active acupuncture (3.8mmHg versus 3.6mmHg) (Macklin et al., 2006). It is interesting to note that Macklin et al.’s (2006) trial used the largest number of acupoints, thirty-two, and it is possible this approach diluted their findings.

3.2.4 Sustainability of the Effects of Acupuncture on Hypertension

Only two of the trials selected for inclusion in this review included a post-intervention follow-up period of a sufficient length to determine if the effects of acupuncture on hypertension are sustainable (Macklin et al., 2006: 12-month follow-up; Flachskampf et al., 2007: 6-month follow-up). In Macklin et al.’s (2006) trial, the effects of the acupuncture on participants’ blood pressure began to diminish from 10 weeks post-intervention. In Flachskampf et al.’s (2007) study, participants’ mean blood pressure approximated mean baseline blood pressure from 12 weeks post-intervention. This suggests the effects of acupuncture on hypertension are not sustainable.

3.2.5 Negative Effects of Acupuncture for the Management of Hypertension

Two-thirds of the trials (n=4, 66.7%) identified adverse events associated with acupuncture. These included “hypertensive urgencies” (Macklin et al., 2006: p.842), minor pain at the acupuncture site (Flachskampf et al., 2007; Kim et al., 2012), minor haematoma and/or bleeding at the acupuncture site (Kim et al., 2012; Zheng et al., 2018) and minor nausea during acupuncture (Zheng et al., 2018). In all four of these studies, adverse events occurred more frequently in the intervention group than in the control group. However, two of the trials calculated the significance of adverse events, and both concluded that the risk of an adverse event associated with acupuncture was no more significant than the risk of and adverse event associated with sham acupuncture (Macklin et al., 2006: p>0.68; Zheng et al., 2008: p=0.147).

3.3 Critical Review

The critical appraisals of the randomised controlled trials selected for inclusion in this review, presented in Appendix 8, show that each trial is of acceptable methodological quality. When the trials are pooled and synthesised for the purposes of a systematic review, however, problems arise. There are also complexities associated with aspects of the randomised controlled trial methodology. These limitations are critically examined in the following sections of the review.

3.3.1 Use of Acupuncture in the Trials

The most significant limitation of the trials selected for inclusion in this review is that no two studies test precisely the same acupuncture protocol. As shown previously, there were differences among the trials in terms of the type of acupuncture used (Chines versus Korean). Subsequently, there were differences in acupoints accessed, the duration of the intervention, the number of acupuncture sessions (overall and per week), and the duration of each session.

As explained by Webb and Roe (2007: p.47), when there is major disparity between the studies included in a review, this can result in the “comparison of apples and oranges” – a meaningless activity. However, due to the paucity of literature on the topic of acupuncture for hypertension, disparities in acupuncture protocols are an unavoidable limitation, and this was also identified in the Cochrane systematic review on the topic (Yang et al., 2018). Disparities in the protocols used in the trials selected for inclusion in this review did, however, prevent a meta-analysis being undertaken, and so the review findings could only be presented in simpler narrative form.

Another problem associated with the use of acupuncture in the trials selected for inclusion relates to the prescription of the acupuncture, and specifically the identification of the acupoints used in the treatments. In Traditional Chinese Medicine, acupoints for the treatment of a particular disorder are selected from a group of acupoints according to each patient’s unique physiology, underlying diagnoses and/or current physical wellbeing (Fang et al., 2013). This was the case for three of the trials selected for inclusion in this review (Macklin et al., 2006; Flachskampf et al., 2007; Zheng et al., 2018). Another two of the trials tested either one acupoint (Zheng et al., 2016) or two acupoints (Kim et al., 2012) on all participants. The last trial took a semi-individualised approach, diagnosing some acupoints and pre-selecting others (Yin et al., 2013). It is unclear, therefore, if an indvidualised or standardised diagnostic approach is best. It is interesting to note that the trial by Macklin et al. (2006) did include groups receiving both standardised and individualised acupuncture, but the results were pooled for reporting.

A further problem associated with the use of acupuncture in the trials selected for inclusion relates to the fact that each of the trials measured participants’ blood pressure at different times during and following the acupuncture treatment. A case study has shown that the effects of acupuncture on hypertension may peak at around 1.5 weeks and 3.5 weeks during the intervention period (Zhang et al., 2014). Blood pressure readings are, therefore, likely to differ depending on when, in relation to these peaks, measurements are taken from patients.

3.3.2 Confounding in the Trials

Another major limitation of the trials selected for inclusion in this review relates to confounding. ‘Confounding’ occurs when an extraneous variable – one which is not of primary interest to, but exists as part of, a trial – affects the findings (Keele, 2011). In this review, confounding is a problem in each individual trial, and it is amplified when the trials are pooled and synthesised.

The primary confounder relates to the use of anti-hypertensive medications. In half of the trials (n=3, 50.0%), patients were permitted to take prescribed anti-hypertensive medications during the intervention and follow-up periods, provided the type and dose of anti-hypertensive medication remained unchanged throughout these periods (Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2016). In the other three trials, patients were not permitted to take any anti-hypertensive medications, and were weaned from these medications where needed prior to the commencement of the intervention (Macklin et al., 2006; Kim et al., 2012; Zheng et al., 2018).

A cohort study has shown that acupuncture in combination with anti-hypertensive medications can facilitate a “significant reduction in blood pressure” (Cevik & Iseri, 2013). Therefore, it is possible that the trials in this review which administered acupuncture in combination with anti-hypertensive medications recorded a greater treatment effect; indeed, these three trials were either strongly or moderately supportive of acupuncture for the management of hypertension (Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2016). Confounding in relation to anti-hypertensive use is further complicated by the fact that although patients were asked not to change the type or dose of their anti-hypertensive medication during the trial, there is no guarantee that this did not occur because, as an extraneous variable, this was not followed up.

The use of anti-hypertensive medications in some of the trials also had another important impact on this review. The average baseline blood pressures for the participants in the trials selected for inclusion – 140.6mmHg (systolic) and 88.9 (diastolic) – were noted previously. The average baseline systolic blood pressure is only slightly higher than the definition of hypertension used by most of the studies (140.0mmHg), cited earlier. The average baseline diastolic blood pressure is actually slightly lower than the definition of hypertension used by most of the studies (90mmHg). One explanation for this is that many of the patients in the trials were taking anti-hypertensive medications. Subsequently, across the studies, the acupuncture intervention was trialed on a group of patients who, at worst, had only minor hypertension. 

Another important confounder affecting the trials selected for inclusion in this review is that they included patients with different types of hypertension. As noted previously, half of the trials included patients with essential hypertension only (Yin et al., 2007; Zheng et al., 2016; Zheng et al., 2018), while the others also included patients with secondary hypertension (Macklin et al., 2006; Flachskampf et al., 2007; Kim et al., 2012). Secondary hypertension in adults may have a variety of causes, including – but not limited to – atherosclerotic renal arterial stenosis, renal failure and hypothyroidism (Charles et al., 2017). It is reasonable to assume that if acupuncture is to be effective at managing patients with secondary hypertension, the underlying cause of the hypertension must be addressed, either through acupuncture of another treatment. Indeed, the three trials which included patients with secondary hypertension returned less-positive results about the use of acupuncture for the management of hypertension than the other three trials.

The problems associated with the inclusion of pre-hypertensive patients in the trial by Yin et al. (2007) must also be noted. In Western medicine, pre-hypertension is typically controlled through non-pharmacological interventions such as a low sodium diet, weight reduction and increased physical activity, etc. (Zhang & Li, 2011). These interventions also benefit patients with hypertension, but in these patients anti-hypertensive medication is also usually prescribed (Zhang & Li, 2011). It is unclear if there are also differences in the activity and effectiveness of acupuncture in patients who are pre-hypertensive, versus those with hypertension.

As noted, there are a variety of modifiable ‘lifestyle’ factors which impact hypertension – including the consumption of sodium, body mass index (BMI) and level of physical activity (Zhang & Li, 2011). Most of the trials (n=5, 83.3%) reported patients’ baseline BMI (Macklin et al., 2006; Flachskampf et al., 2007; Yin et al., 2007; Kim et al., 2012; Zheng et al., 2018); however, only one of the studies controlled for this in the analysis (Macklin et al., 2006). None of the studies controlled for potential confounders such as sodium intake or level of physical activity. It is possible that patients enrolled in a trial about hypertension may become more aware of, and more willing to change, the modifiable factors associated with their condition. However, none of the trials selected for inclusion measured this as a potential confounder.

It is also important to note that two of the trials recorded significant rates of participant loss-to-follow-up: Flachskampf et al. (2007: 27/160 lost, 16.0%) and Kim et al. (2012: 5/33 lost, 15.2%). These losses may have occurred because participants chose to leave the study (e.g. because the time commitment to participate was too great), or because participants were eliminated from the study (e.g. because they developed significant illness) (Flachskampf et al., 2007; Kim et al., 2012). It is possible that the results of a study will be biased if participants who are lost to follow-up are systematically different to those who remain in the study (Polit & Beck, 2010). For example: it is possible that people who were lost to follow-up were more seriously unwell, perhaps because of more significant hypertension, than patients who remained; thus, those who remained had less-serious hypertension more responsive to acupuncture. However, it is impossible to determine this as neither Flachskampf et al. (2007) nor Kim et al. (2012) reported the demographic characteristics or, where available, trial data of patients lost to follow-up.

3.3.3 Problems with the Trial Methodology

There are a number of limitations associated with the methodology of the trials selected for inclusion in this review. As noted, all six of the studies were randomised controlled trials, as these produce the highest quality of primary evidence to inform clinical practice (Oxford Centre for Evidence-Based Medicine, 2009). However, the use of randomised controlled trials for research on acupuncture has been strongly criticised (McDonald, 2019). This is because randomised controlled trials attempt to measure a single variable whilst controlling for all others – however, and as shown throughout the previous section of this review, acupuncture is associated with a variety of variables which may not be easily controlled (McDonald, 2019). Further complicating this is the fact that acupuncture’s mechanism of action in relation to hypertension is still largely unclear (Li et al., 2019). Thus, some authors go so far as to claim that randomised controlled trials for acupuncture are “inappropriate” (McDonald, 2019: p.47).

There are also problems associated with the use of sham acupuncture as a control in the trials selected for inclusion in this review. Most of the studies (n=5, 83.3%) used sham acupuncture where needles were inserted at acupoints not related to hypertension (Macklin et al., 2006; Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2016; Zheng et al., 2018). The alternative is to place needles at actual acupoints, but at a superficial depth (Lin et al., 2012). However, both approaches to sham acupuncture have been strongly criticised because there is no evidence that either is inert, and so both may influence patient outcomes (McDonald, 2019).

It has also been argued that sham acupuncture delivers a placebo effect (Xiang et al., 2018). McDonald (2019) goes so far as to suggests that the placebo effect may explain up to 30.0% of all treatment effects seen in randomised controlled trials of acupuncture interventions where sham acupuncture is used. If this was the case in the studies selected for inclusion in this review, the positive effects of acupuncture on hypertension would be significantly exaggerated. This was suggested in a recent meta-analysis on the use of acupuncture for pain, where trials involving sham acupuncture were far more likely to report positive findings (Chen et al., 2016).

It is also noteworthy that none of the studies selected for inclusion in this review involved blinding. ‘Blinding’ occurs when clinicians and/or patients are made unaware of whether an intervention or a control treatment is being delivered, thereby reducing the risk of bias (Polit & Beck, 2010). The blinding of both clinicians and patients can be achieved in randomised controlled trials on acupuncture using placebo needles and/or needle tubes, though patients who are experienced with acupuncture may guess a placebo needle is being used because it produces a different sensation to a real needle (Lin et al., 2012). Again, there is also no evidence that placebo needles or needle tubes are inert, and no evidence about which type of sham device is more effective (Zhang et al., 2015). Nevertheless, blinding of clinicians and patients is an important consideration for future trials testing acupuncture for hypertension.

A final limitation of the studies selected for inclusion is that many included small cohorts. As noted, the studies selected for inclusion involved an average of 147 participants, ranging from 30 patients (Zheng et al., 2016) to 428 patients (Zheng et al., 2018). Three of the trials included <50 participants (Yin et al., 2007: 40 patients; Kim et al., 2012: 33 patients; Zheng et al., 2016: 30 patients). When a cohort is small, this increases the likelihood that it is not representative of the broader population (Moule & Goodman, 2009) – for example: in Kim et al.’s (2012) study males were strongly over-represented, and in Zheng et al.’s (2016) study the opposite occurred. A non-representative sample is particularly likely if the cohort has been recruited through the use of non-probability convenience sampling (Gray et al., 2013), as in all six of the studies. Studies with non-representative cohorts lack external validity (Burns & Grove, 2011), and so it is difficult to accurately apply their findings to other populations beyond the study cohort. 

4.0 Discussion

4.1 Findings in the Context of the Broader Literature

As shown in the previous section, the six randomised controlled trials selected for inclusion in this review were inconclusive about whether acupuncture, in comparison to sham acupuncture, is effective at reducing systolic and/or diastolic blood pressure in people with hypertension. Based on these findings, it seems reasonable to conclude that acupuncture may, but will not necessarily, have a positive effect on hypertension. It also seems reasonable to conclude that acupuncture is unlikely to cause harm to those who choose to use it. However, this must be understood in the context of the broader literature on acupuncture and hypertension.

Half of the trials (n=3, 50.0%) concluded that active acupuncture is more effective than sham acupuncture for reducing blood pressure in people with hypertension (Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2018). Across these three studies, the blood pressure of people receiving acupuncture decreased by an average of 7.0mmHg. It is uncertain whether this can be considered a ‘significant’ reduction in clinical or physiological terms. This is particularly true considering the research which shows that treatment with anti-hypertensive medications reduces blood pressure by an average of 13.6mmHg (systolic, for single medications) to 17.3mmHg (systolic, for combination medications) (Bronsert et al., 2013). Law et al. (2009) suggests that a reduction of ≥10mmHg (systolic) must be achieved if the person’s risk of hypertension-related cardiovascular disease is to be significantly reduced.

This review has shown that not only are the effects of acupuncture on a person’s blood pressure small, these effects are also variable: although half of the trials concluded that active acupuncture is more effective than sham acupuncture for reducing blood pressure in people with hypertension, the other half (n=3, 50.0%) returned less-positive results (Macklin et al., 2006; Kim et al., 2012; Zheng et al., 2016). If a patient were to choose to undergo acupuncture for their hypertension, it therefore seems reasonable that a nurse recommends they continue with their prescribed anti-hypertensive medication – that is, that acupuncture is used as an adjunctive treatment. However, it must be emphasised that this review did not consider the effects of acupuncture alone versus acupuncture in combination with anti-hypertensive medications (though half of the trials selected for review permitted patients to take anti-hypertensive medications while receiving acupuncture [Flachskampf et al., 2007; Yin et al., 2007; Zheng et al., 2016]). As two or more anti-hypertensive medications may have a cumulative effect on lowering a person’s blood pressure (Bronsert et al., 2013), it is possible that anti-hypertensives plus acupuncture may have the same effect. Further research on acupuncture in combination with anti-hypertensive medications is important to inform practice. 

Another important finding from this review is that the effects of acupuncture on hypertension are unlikely to be sustainable beyond the intervention period (Macklin et al., 2006; Flachskampf et al., 2007). This is problematic because essential hypertension is a chronic disease and one, therefore, which requires effective long-term management (Chen, 2012). If a patient were to choose to undergo acupuncture for their hypertension, it therefore seems reasonable that a nurse recommends they participate in regular ongoing acupuncture sessions, rather than a single block of sessions. However, it must be emphasised that none of the trials selected for inclusion in this review included an intervention period of beyond 8 weeks. Further research on the effects of continuous or ongoing acupuncture sessions on hypertension is important.

It must also be emphasised that only needle acupuncture was tested in the trials selected for inclusion in this review. However, there are a variety of other types of acupuncture which may be used in clinical settings – including, for example, laser acupuncture, electro-acupuncture and warm needling (Li et al., 2018). Some of these approaches, and particularly laser acupuncture, do not necessarily require a clinician to have advanced TCM training (Litscher et al., 2012); therefore, they may be simpler for nurses to apply in routine practice. Again, further research on the effects of other types of acupuncture on hypertension is important to inform practice.

4.2 Future Research on Acupuncture for Hypertension

As shown in the previous section, to enable evidence-based practice, there is a need for ongoing, quality research on the topic of acupuncture for hypertension. The problems with the use of randomised controlled trials for acupuncture research were critically analysed earlier. Because of these problems, other methodologies should be considered for future research.

For example: Cevik and Iseri (2013) conducted a high-quality longitudinal cohort study to investigate the effects of acupuncture on hypertension. As stated by Houser (2018: p.266), the longitudinal cohort study methodology provides a “powerful way” of assessing the effects of interventions over time. Longitudinal cohort studies are also ideal for investigating the effects of treatments on chronic conditions like hypertension (Schneider et al., 2013). This methodology is therefore an important consideration for future research on acupuncture for hypertension.

4.3 Findings in the Context of Other Randomised Controlled Trials

In addition to the Cochrane systematic review cited earlier (Yang et al., 2018), there are also a number of other systematic reviews and meta-analyses published in the previous decade which investigate the effects of acupuncture on hypertension. Each of these studies used different methodologies with different selection criteria to this review, and none included the same six randomised controlled trials selected for inclusion in this review. However, all of these studies agree with the findings of this review: that acupuncture may, but will not necessarily, have a positive effect on reducing the blood pressure of a person with hypertension (Lee et al., 2009; Wang et al., 2013; Li et al., 2014; Zhao et al., 2019). In the systematic reviews and meta-analyses where the safety of acupuncture for hypertension was also investigated, the studies also agreed that acupuncture was safe (Wang et al., 2013; Li et al., 2014; Zhao et al., 2019).

These systematic reviews and meta-analyses also came to the same conclusion as this review regarding the lack of heterogeneity in the primary studies about acupuncture for hypertension (Lee et al., 2009; Wang et al., 2013; Li et al., 2014; Zhao et al., 2019). In all studies, this caused difficulties with drawing robust conclusions and creating trustworthy evidence to inform practice. This again highlights the importance of ongoing, quality research on the topic, noted previously.

4.4 The Nurse’s Role in Acupuncture for Hypertension

It is important to consider the nurse’s role in acupuncture for hypertension. As shown previously, the nurse certainly has a role in supporting and educating patients who choose to undergo acupuncture for their hypertension. They may also have a role in recommending acupuncture for hypertension, in patients who may be interested in this as an adjunctive to anti-hypertensive medication. In both cases nurses must inform patients of the limitations of acupuncture for hypertension, and particularly in relation to the fact that acupuncture may have no effect.

Where it is appropriate to the clinical setting, it may also be possible for nurses to administer acupuncture to patients with hypertension. Zheng et al. (2018) caution that clinicians who administer acupuncture must be appropriately trained and qualified to do so. However, the development of modern, novel forms of acupuncture – like laser acupuncture – mean nurses may not necessarily require advanced TCM training to administer acupuncture (Litscher et al., 2012). Zheng et al. (2018) also emphasise the importance of developing simple protocols to enable acupuncture for hypertension to be administered in routine clinical practice. Nurses must always work within their scope, and the policies and procedures of the clinical setting where they practice. However, nurses’ role in administering acupuncture is a key future consideration.

4.5 Limitations of the Review

The limitations of the randomised controlled trials selected for inclusion in this review were critically analysed in a previous section. There were also limitations of the review methodology itself. The findings of the review must be understood in the context of these limitations.

Most significantly, the review was limited to studies published in or translated into English. As noted, this was necessary because there was no scope in this review for translation. However, Higgins and Green (2011) suggest that the use of an English-language limiter inevitably results in the exclusion of studies which are relevant to the research topic. This is a particular problem in relation to studies on acupuncture: as it is a TCM therapy, it is reasonable to assume that there are a large number of trials on acupuncture for hypertension in Chinese languages.

The review also has a number of other limitations. For example: only a small number of databases were searched, and it is possible that more relevant studies would have been identified if additional databases were searched. The review was limited to studies which used a randomised controlled trial methodology, despite the limitations of this methodology for research on acupuncture. Further, the review was limited to studies which tested needle acupuncture and used sham acupuncture as a control treatment, even though a variety of other randomised controlled trials on acupuncture for hypertension were identified. These are important considerations for future systematic reviews investigating acupuncture on hypertension.

5.0 Conclusion and Recommendations

This systematic review was undertaken to answer the research question, ‘In patients with hypertension, is acupuncture, in comparison to sham acupuncture, effective at reducing systolic and/or diastolic blood pressure?’ Comprehensive searches were undertaken on five of the largest electronic databases. From the 102 relevant studies identified in the searches, six randomised controlled trials were selected for critical analysis, quality appraisal and synthesis.

The trials selected for inclusion in this review were inconclusive about whether acupuncture, in comparison to sham acupuncture, is effective at reducing blood pressure in people with hypertension. Some of the trials selected suggested that acupuncture is more effective than sham acupuncture at reducing blood pressure, while others found it might be more effective, and another found it was not more effective. None of the studies identified significant harms associated with the use of acupuncture for hypertension. It seems reasonable to conclude that acupuncture may, but will not necessarily, have a positive effect on hypertension. It also seems reasonable to state that acupuncture is unlikely to cause harm to those who choose to use it.

It must be emphasised that there were a number of limitations with the studies selected for inclusion in this review, particularly when their findings were synthesised. Significantly, there were differences among the trials in terms of the type of acupuncture used (Chines versus Korean) and, as a result, in the acupoints accessed, the duration of the intervention, the number of acupuncture sessions (overall and per week), and the duration of each session. There were also problems associated with confounding in the studies – including in relation to the use of anti-hypertensive medications, the inclusion of patients with essential and secondary hypertension, the failure to control for the modifiable ‘lifestyle’ factors which impact hypertension, and the use of small cohorts. Further, there were complexities associated with the use of the randomised controlled trial methodology, which may not be suitable for studies on acupuncture, and controls treated with sham acupuncture, which may not be an inert treatment.

Subsequently, the trials selected for inclusion in this review do not provide high-quality evidence to inform clinical practice in relation to the use of acupuncture for the management of hypertension. The findings of this review must be applied in consideration of this limitation.

Based on the review’s findings, two evidence-based recommendations have been developed:

For nursing practice: Nurses may recommend, provide education on and (where they are trained and qualified to do so) administer acupuncture to patients with hypertension who choose to use acupuncture. Nurses should ensure patients understand that although acupuncture may not necessarily have an effect on their hypertension, it is unlikely to cause them harm.

For future research: Additional research on acupuncture for hypertension is essential to further informing evidence-based practice in relation to this topic. In particular, research must be conducted to determine the effects of acupuncture in combination with anti-hypertensive medication, the effects of continuous/ongoing versus block acupuncture sessions, and the effects of other types of acupuncture (e.g. laser acupuncture, electro-acupuncture, warm needling, etc.) on hypertension. This research should consider the methodological limitations noted above. Randomised controlled trials and other research methodologies should be used.

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Appendices

Appendix 1: PICO

Appendix 2: Keywords

Appendix 3: Inclusion and Exclusion Criteria

Appendix 4: Results from Database Searches

Appendix 5: PRISMA Diagram of Search Results

Additional records identified through other sources
(n = 0)

Records identified through database searching
(n = 102)

Identification

Records after duplicates removed
(n =102)

Screening

Records excluded
(n = 87)

Records screened
(n = 102)

Full-text articles assessed for eligibility
(n = 15)

Eligibility

Studies included in literature review
(n = 6)

Included

Full-text articles excluded, with reasons
(n = 9)

• N=4: not a randomised controlled trial
• N=3: a trial which did not include a sham acupuncture group
• N=1: not published in a peer-reviewed journal
• N=1: not available in English in full-text

Appendix 6: Overview of Selected Studies

Appendix 7: Data Extraction

Appendix 8: CASP Critical Appraisal