trial is warranted to clarify this issue. Second, the multivariable
analysis does not take into account unmeasured
variables and can not establish a cause-effect relation.
The confounding effect of unmeasured variables can not
be excluded. Nevertheless, many relevant variables were
considered. Third, similar to previous observational [1-3]
and interventional studies [9,10], the impact of blood
transfusions given before and after the ICU stay on outcome
was not evaluated and the indication for blood
transfusion was not identified. Fourth, the indication for
blood transfusion was not considered in our analysis and
may have been an important confounding factor. However,
indication for blood transfusion is usually influenced
by hemoglobin concentrations, comorbidities, and
severity of illness, all of which are factors that were considered
in our analysis. Finally, the results of our study
may not be extrapolated to patients with other case
mixes, such as medical patients