investigate this issue, observational studies such as ours
can provide insight, generate hypotheses, and complement
the results of randomized studies. Randomized
controlled studies in which subjects are randomized to
two different therapeutic strategies, independent of their
needs, are at risk of therapeutic misassignment [26].
Exclusion of subgroups of patients according to study
protocol, dropout of others due to declined consent or
non-compliance of physicians, and failure of recruitment
are all factors that hinder extrapolation of the results of
randomized controlled trials to other patient populations
with different case mixes. Changes in practice and quality
of care over time may be another important factor that
necessitates reassessment of current treatment strategies.
Although the TRICC study [9] demonstrated that a
restrictive strategy of blood transfusion was as effective
as a liberal strategy, leukoreduction was not implemented
at the time that study was performed. Whether or not the
results of the TRICC study have changed transfusion
practice in ICUs is unclear. The mean pre-transfusion