Transfusion Practice and Mortality in Cardiac Patients
Abstract & Commentary
Synopsis: Anemia increases the risk of death in critically ill patients with cardiac disease, and blood transfusions appear to decrease this risk.
Source: Hébert PC, et al. Am J Respir Crit Care Med 1997;155:1618-1623.
In this cohort study, investigators in six canadian tertiary level ICUs studied all adult, non-brain dead patients admitted during 1993 to determine the impact of transfusion on mortality rates in critically ill patients. The study population consisted of 4470 consecutive patients60% who were prospectively enrolled and 40% who were identified by retrospective record review. The incidence of anemia (blood hemoglobin level < 9.5 gm/dL) at some time during their ICU stay was 40% among patients who survived and 56% in nonsurvivors (P < 0.0001). Overall, 31% of all patients received red blood cell transfusions while in the ICU28% of the survivors and 42% of the nonsurvivors (P < 0.0001). In all patients, the adjusted odds ratio (OR) for mortality was 0.61 after one to three units of transfusion and 0.49 after four to six units, suggesting that transfusion decreased mortality in these patients.
The only diagnostic subgroup within the 4470 patients in which this overall observation was consistently seen was patients admitted because of cardiac disease; critically ill patients with cardiac disease appeared more likely to die the more anemic they were, and transfusion was associated with better survival. In the subgroup with cardiac disease, increasing hemoglobin values in anemic patients was associated with improved survival (OR = 0.80 for each increase in hemoglobin of 1.0 gm/dL, P = 0.012).
COMMENT BY DAVID J. PIERSON, MD
In the era of human immunodeficiency virus (HIV) infection, there has been increased awareness of blood-borne pathogens and the risks of transfusion. In addition, several studies have examined transfusion practice in patients undergoing coronary artery bypass grafting and concluded that administering fewer red blood cell transfusions than in the past may be safe. However, these findings may not apply to the critically ill, in whom the effects of anemia on systemic oxygen delivery and cardiac demand may assume greater importance.
This study supports the concept that, among patients with compromised cardiac function, the further insult of anemia can have an adverse impact in terms of overall survival. The findings support the conclusion of a small case control study (Nelson AH, et al. Crit Care Med 1993;21:860-866), which found that cardiac complications following high-risk cardiovascular surgery were more common with increasing severity of anemia. The "optimal" hemoglobin level for critically ill patients with cardiac disease is yet to be determined, but this study lends support to a more liberal transfusion policy in this patient category than has sometimes been employed in recent years.
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