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.