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Ann Thorac Surg 2007;83:2260-2261
© 2007 The Society of Thoracic Surgeons
The Cleveland Clinic Foundation, Department of Cardiothoracic Anesthesia (G-3), 9500 Euclid Ave, Cleveland, OH 44195
(Email: kochc{at}ccf.org).
We welcome comments from Zacharias and colleagues [1] on our recent article [2] on functional health-related quality of life and red blood cell transfusion in cardiac surgery. The authors expressed that a conservative approach to red blood cell transfusion is appropriate in light of increasing amounts of data reporting complications associated with transfusion [3, 4]. However we disagree with the authors that the take home message of the article is to withhold transfusion of red blood cells for those patients who need it. The authors state that "patients who drop their hematocrit postoperatively benefit from blood and it should be used when it is felt justified." We could not agree more—our concern is "when it is felt justified" and it is our recommendation for increased measures of restraint when considering red blood cell transfusion. Red blood cell transfusion in cardiac surgery is largely based on institutional preferences and anecdotes to guide many transfusion decisions, rather than evidenced-based medicine. Our article states that in light of increasing amounts of data it is best to avoid transfusion whenever possible, whereas recognizing it is necessary in some. Our take home message is that there is risk-balance to red blood cell transfusion. Increasing work in the area of transfusion has highlighted the risk side of the equation. Therefore, be conservative with red blood cell transfusions whenever possible.
The authors also comment, "We have also read with interest the previous paper from the same authors suggesting a reduction in morbidity and mortality in patients transfused with blood after coronary surgery." The authors incorrectly interpreted the findings of our other recent publication [5]. Patients who were transfused with red blood cells had a risk-adjusted incremental increase in morbid outcomes with increasing units of red blood cells administered, rather than a reduction in morbidity and mortality as the authors’ stated.
The authors comment that unadjusted demographic characteristics and perioperative variables differed among the groups under comparison. They stated that "the authors have tried to make the best possible case despite starting with two completely different groups [on DASI scoring preoperatively] that the impact on quality of life is purely related to blood transfusion." The fact that the groups differ at baseline is not surprising as it is true for most observational cohort investigations in cardiothoracic surgery in which there is a nonrandom allocation of treatment. We analyzed the data set and adjusted for the uneven distribution of risk factors with advanced variable selection procedures (bootstrap aggregation techniques) and unique application of multivariable ordinal regression modeling to account for "ceiling" and "floor" effects due to the nature of quality of life data. The extensive list of demographics, co-morbidity, operative factors, blood component therapy, as well as postoperative morbid events was considered in the variable selection procedure. The results of the multivariable ordinal regression modeling are not to be interpreted as "the impact of quality of life is purely related to blood transfusion." Correct interpretation of our analyses is that red blood cell transfusion has an impact on health-related quality of life in addition to other variables. "Purely" is defined as "only or completely" and should not be interpreted that red blood cell transfusion in isolation impacts quality of life. The relationship between health-related quality of life is more complex and is related to other variables as well as red blood cell transfusion.
The authors also comment that "of course, smaller body surface area, lower hematocrit and higher age at surgery in the transfused group compared with the nontransfused group makes the conclusion even more difficult to accept" and we disagree with the statement that these factors make our findings "difficult" to accept. We invite the authors to more closely examine our statistical methods section. With the bootstrap aggregation techniques and the multivariable ordinal modeling, the specific factors the authors put forth were considered in our statistical modeling. Our results can be interpreted as: all things being equal; red blood cell transfusion has a persistent impact on health-related quality of life following cardiac surgery.
The authors ask "if there were any unknown variables that may not have been corrected for, which could have affected the outcomes?" As with any nonrandomized trial there could be unknown and unaccounted variables unevenly distributed among groups under comparison. However, to the extent possible for this well-studied population we considered all available known risk factors that have been associated with outcome in this particular patient population. With regard to controlling for the leukocyte-reduced status of the units, our data set precedes the introduction of universal leukocyte-reduced red blood cells, which occurred in 2002.
Finally, we have also recognized from prior investigation [6] that women report less adjusted overall functional recovery gains as compared with men, and have therefore appropriately adjusted for this observation in our statistical modeling.
Greater awareness of associated risk, increased investigation in the form of prospective trials, development of real-time bedside monitoring of tissue oxygenation will further our understanding of the complex risk-benefit relationship of blood transfusion in our cardiothoracic surgery population and enable us to provide optimal care for this patient population.
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