To the Editor: Dr Wu and colleagues1 reported the results of a large retrospective cohort study to determine the prevalence of abnormal preoperative hematocrit levels and the association of this abnormality with postoperative mortality and cardiac events in elderly patients undergoing noncardiac surgery. They demonstrated a negative association with both low and high preoperative hematocrit levels.
The correlation between low preoperative hematocrit and these outcomes is supported by the established association between anemia and cardiac events.2 More controversial is the association between polycythemia and postoperative outcome. An association between polycythemia and thrombosis has been shown,3 but in the absence of intraoperative blood transfusions for these patients, it is likely that hematocrit levels after surgery would be decreased. Furthermore, patients undergoing surgery usually receive thromboprophylaxis.4 These 2 conditions should at least partially protect patients with polycythemia from thrombotic events.
In a study of hemoglobin variation in women undergoing chemotherapy followed by surgery for locally advanced cervical cancer, analysis of the variation of hemoglobin during surgery showed an expected direct correlation between preoperative and postoperative hemoglobin levels. Furthermore, higher preoperative hemoglobin levels were associated with greater operative hemoglobin decreases (r = –0.46; P < .001). The results were consistent after exclusion of women who received blood transfusions.5
Primary end points of that study were different from the study by Wu et al, and some confounding factors that might have accounted for the observed association were not taken into consideration. However, if this observation were confirmed, it is possible that the association of adverse outcomes with polycythemia could be partially ascribed to a greater decrease in hematocrit in patients with polycythemia. The systemic (and, particularly, cardiovascular) effect of different hemoglobin levels might be dependent on acute variation in concentration in addition to absolute values. Several guidelines on blood transfusion regimens or other prophylactic and therapeutic strategies primarily give recommendations based solely on absolute values, not hematocrit variations.6
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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