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 illus
