Vasovagal reactions (VVR) are an important adverse effect following phlebotomy that has been increasingly associated with donor lapse from subsequent donation. Applied Muscle Tension (AMT) is seen as a means to mitigate this risk of said reactions by temporarily increasing blood pressure during donation through repetitive tension of major muscles. This meta-analysis aims to evaluate AMT's effectiveness in preventing vasovagal reactions among blood donors through number of events and Blood Donation Reactions Inventory (BDRI) scale, which evaluates 11 prevalent symptoms associated with blood donation on a scale ranging from 0 to 5.

The databases PubMed, Scopus, Embase, Web of Science and Cochrane were searched for relevant abstracts published until August 2023. The search yielded 111 original papers following duplicate removal. Results were screened for randomized clinical trials relevant to the theme of this review. Two independent and blind reviewers participated in each step of the article selection with a third reviewer to solve any conflicts, in accordance with PRISMA guidelines.

Three randomized trials, involving 500 participants in the AMT group and 496 participants in the control group, were included. A random effects analysis yielded a pooled risk ratio of 0.51 (95% CI: 0.37 - 0.69) (Z = 4.25, p < 0.0001) for vasovagal reactions in the AMT group compared to the control group. Additionally, the studies demonstrated low heterogeneity (I² = 0%), indicating consistency in effect sizes. A subsequent mean difference analysis was conducted based on four papers which evaluated BDRI scores establishing a 0.14 difference favoring intervention (95% CI: 0.08 - 0.21).

The meta-analysis findings support AMT as an effective intervention for reducing vasovagal reactions among blood donors with a Number Needed to Treat of 12. Given the well-established role of Vasovagal Reactions as deterrents to subsequent donation among blood donors, implementation of said strategies may prove to be a valuable tool in preventing donor lapse. The consistency of effect sizes, evidenced by low heterogeneity (I² = 0%), further strengthens the validity of the pooled results. However, limitations such as the small number of studies and differences in intervention protocols and outcome measures warrant cautious interpretation.

This meta-analysis establishes AMT as an effective approach for reducing vasovagal reactions during blood donation. The intervention may enhance the donor's overall experience and potentially increase donor retention rates. Further research is needed to explore long-term effects and optimize AMT's integration into blood donation practices.