Red cell transfusion: an essential factor for patient prognosis in surgical critical illness?

In contrast to randomized studies, previous cohort studies identified red cell transfusion as an independent predictor of mortality in critically ill patients. However, these cohort studies did not adjust for disease severity during intensive care unit (ICU) stay. We performed a retrospective, observational cohort study using prospectively collected data from March 1, 1993, through February 28, 2005. A cohort of 3037 consecutive surgical cases requiring intensive care therapy for more than one day was analyzed. We used two different sets of potentially confounding covariables (admission variables only or in combination with variables reflecting number and extent of organ dysfunction during ICU stay). We found that the total number of red cell units which a case had received during ICU stay, and the maximum number of units given on a single day, were independently associated with an increase in ICU mortality when only admission variables were considered for the analysis. After controlling for the additional effect of variables reflecting organ dysfunction during ICU stay, we found that red cell transfusion was no longer an independent risk factor for death. However, there was a significant effect of red cell transfusion on ICU LOS in survivors irrespective of the covariable sets used. We conclude that red cell transfusion during ICU stay may be only a surrogate marker for disease severity and is not causally related to ICU mortality. Relevant side effects of red cell transfusion are presumably small and may be only recognizable in surviving cases.