CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Karin H. Humphries, MBA, DSc*,
Min Gao, PhD,
Aihu Pu, MSc,
Samuel V. Lichtenstein, MD, PhD and
Christopher R. Thompson, MD
* Division of Cardiology, St. Paul’s Hospital, 620B-1081 Burrard Street, Vancouver, British Columbia V6Z 1Y6, Canada (Email: khumphries{at}providencehealth.bc.ca).
We thank Drs. Habib and Zacharias for their thoughtful comments on our manuscript (1). First it is important to clarify that the significant 42% higher 30-day mortality in women reported in our study refers to the overall 14-year time frame of the study and does not imply that a 42% difference still persists at the end of our study period. Quite the contrary, the gap narrowed significantly.
We certainly agree with the authors that coronary vessel size is not the only important factor associated with body size. Specifically, the adverse effects of greater on-pump hemodilution and more frequent administration of packed red blood cells in patients with small body size suggests that women would be differentially affected. These aspects would be interesting to evaluate, especially because they are not intrinsic patient characteristics but potentially modifiable processes of care. Unfortunately, our database did not reliably capture this information.
Nevertheless, it is important to point out that even if we could undertake the suggested analysis, any attenuation in the gender difference that might result from adjustment for red blood cell transfusions and on-pump hematocrit would be unlikely to explain the significant decline in female 30-day mortality over the last 14 years. To attribute the observed decline in mortality to these factors would necessitate a very large decrease in the prevalence of hemodilutional anemia and/or use of blood products differentially in women compared with men. Alternatively, because these characteristics are associated with body size, we would have had to observe a very sharp decline in the proportion of women versus men with small body size. As shown in Table 3 of our manuscript, the proportion of women with small body size changed very little in our dataset over the last 14 years.
In light of the evidence that hemodilution (2,3) and frequent transfusions are associated with adverse outcomes (4,5), changes in practice, as suggested by the Drs. Habib and Zacharias, would be expected to be of benefit to both women and men.
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References
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- Humphries KH, Gao M, Pu A, et al. Significant improvement in short-term mortality in women undergoing coronary artery bypass surgery (1991 to 2004) J Am Coll Cardiol 2007;49:1552-1558.[Abstract/Free Full Text]
- DeFoe GR, Ross CS, Olmstead EM, et al. Northern New England Cardiovascular Disease Study Group Lowest hematocrit on bypass and adverse outcomes associated with coronary artery bypass grafting Ann Thorac Surg 2001;71:769-776.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, et al. Adverse effects of low hematocrit during cardiopulmonary bypass in the adult: should current practice be changed? J Thorac Cardiovasc Surg 2003;125:1438-1450.[Abstract/Free Full Text]
- Engoren MC, Habib RH, Zacharias A, et al. Effect of blood transfusion on long-term survival after cardiac operation Ann Thorac Surg 2002;74:1180-1186.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, et al. Role of hemodilutional anemia and transfusion during cardiopulmonary bypass in renal injury after coronary revascularization: implications on operative outcome Crit Care Med 2005;33:1749-1756.[CrossRef][ISI][Medline]
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