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Ann Thorac Surg 1995;60:574-575
© 1995 The Society of Thoracic Surgeons
Cardiology Section (151), Denver VA Medical Center, 1055 Clermont St, Denver, CO 80220
There is little doubt in my mind that intraoperative blood transfusion is associated with adverse outcomes at coronary artery bypass grafting in both women and men. The fundamental issue is what is the root cause? Is it the lower preoperative hematocrit and red cell volume as suggested by Utley and colleagues, or is it operative technique or differences in the characteristics of female vessels that led to greater intraoperative bleeding in women, or is it an as yet not understood difference in coagulability in women on cardiopulmonary bypass, or is it a difference in the amount of hemodilution in setting up the pump-oxygenator, or is it an unrecognized difference in the criteria for intraoperative transfusion in women? I do not believe that the data presented in this article allow a definitive answer. How might an answer to the question, ``What is it about women that leads to greater operative mortality and morbidity than men?'' and more importantly, ``How might the processes of care be changed to improve outcomes in women?'' have been obtained?
The design of observational data analyses to assess determinants of outcomes of therapies is a complex art form; however, there are some useful guidelines. My colleagues and I have found it useful to distinguish between patient-related risk factors and processes of care. The former are characteristics that the patient brings with him or her to the episode of care. The latter are acts of care-something a care provider does to or for a patient. In trying to determine whether a process of care has contributed to a particular outcome, we must first adjust for the differences in patient characteristics that may have affected the outcome. The distinction is also important because patient-related risk factors are usually not under the control of the care provider, whereas processes of care nearly always are. We believe that patient-related risk factors should be determined before the episode of care-before entering the operating room in the case of a surgical procedure. We have found the following relationship useful in conceptualizing the roles of processes, structures (the environment in which care is provided together with care provider characteristics), and risk factors in determining outcomes of care: processes of care + structures of care + patient-related risk factors = outcomes of care.
In the present study we would have called intraoperative blood transfusion a process of care, not a risk factor. This is important because true patient-related risk factors that might lead to increased use of intraoperative blood transfusion (eg, preoperative hematocrit, preoperative red cell mass, preoperative coagulation parameters) were not included in the analyses.
Finally, in trying to determine risk factors in a specific subgroup, we believe it is useful to either confine the analyses to this subgroup (ie, women) or to include an identifying covariate (eg, male = 0, female = 1) when analyzing the entire population.
It is difficult to disagree with Utley and associates' recommendations for blood conservation preoperatively. However, given the uncertainties in the analyses, caution should be applied in using the present article to support the more frequent use of homologous transfusion preoperatively.
Related Article
Ann. Thorac. Surg. 1995 60: 570-574.
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