Limitations and Future Research
There are several predominant limitations across the studies discussed in this review. Firstly, retrospective studies populate this area of research and are prone to selection bias as higher-risk Witnesses are more likely to be excluded, therefore studies will not accurately reflect all those in need of surgery. Additionally, a large proportion of the study designs are single-centre and nonrandomized3,8,56. There is an increased likelihood that surgeons will be more cautious when operating on witnesses, this in turn could result in reduced blood loss, which is impossible to measure and thus cannot be accounted for55. However, it is important to note that these research limitations were taken into account and often employed propensity matching to define the control group and minimize such limitations15,56. Nonetheless, this only accounts for variables that were recorded, when in reality there will have been a greater number of confounding variables that could not be included in the propensity matching.
Only one study mentioned cost comparisons for treatment between the two groups and found no significant difference in total costs for Witnesses and their controls46. More research is needed in this area.
Finally, a large proportion of the research discussed in this review consisted of either very small sample sizes2 or included case reports and are therefore subject to all recognised limitations, including retrospective limitations aforementioned, generalizability, causality, information and publication bias, overinterpretation or misinterpretation of data. Future research is needed to provide greater clarity on the outcomes of cardiac surgery in Witnesses that refuse blood products. There needs to be an increased focus on multi-institutional studies with a greater number of participants to validate the research to date8,62, along with readmission rates and long term mortality following discharge2, and a more in depth cost analysis of pre-, intra-, and post-operative optimization of witnesses during cardiac surgery8.