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 pres
