CHICAGO—Older patients with mild degrees of pre-operative anemia (low red blood cell count) or those with a very high red blood cell count have a higher risk of post-operative death or cardiac events following major noncardiac surgery, according to a study in the June 13 issue of JAMA.
Elderly patients are at increased risk for abnormal hematocrit values, according to background information in the article. A hematocrit value is the percentage of a blood sample that consists of red blood cells, measured after the blood has been centrifuged and the cells compacted. Despite nearly universal screening of patients for abnormal pre-operative hematocrit levels, the prognostic implications of pre-operative anemia or polycythemia (an abnormal increase in the red blood cell count) are not well understood, and many reports differ on what hematocrit values could be harmful.
Wen-Chih Wu, M.D., of the Providence Veterans Affairs Medical Center, Providence, R.I., and colleagues evaluated the prevalence of pre-operative anemia and polycythemia and their effects on 30-day post-operative outcomes for 310,311 veterans, age 65 years or older, who underwent major noncardiac surgery between 1997 and 2004 in 132 Veterans’ Affairs medical centers in the U.S. The researchers used data from the VA National Surgical Quality Improvement Program.
Based on pre-operative hematocrit levels, patients were stratified into standard categories of anemia (hematocrit less than 39.0 percent), normal hematocrit (39.0 percent-53.9 percent) and polycythemia (hematocrit 54 percent or greater). The authors estimated increases in 30-day post-operative cardiac events and risk of death in relation to each hematocrit point deviation from the normal category.
The researchers found that 30-day death and cardiac event rates increased incrementally with either positive or negative deviations from normal hematocrit levels. Using these levels, there was a 1.6 percent increase in the adjusted risk of 30-day post-operative death for every percentage point of hematocrit deviation from the normal range. “Thus, a patient with a pre-operative hematocrit value of 30.0 percent has a 14.4 percent increased risk of 30-day post-operative mortality, while a patient with a pre-operative hematocrit of 24.0 percent has a 24.0 percent increase in the risk of 30-day postoperative mortality.”
“Our findings suggest that among older men undergoing elective surgery, the lowest risk of adverse outcomes was in those with pre-operative hematocrit values between 39.0 percent and 50.9 percent. Even minimal deviations from this optimal range were associated with an increased risk of 30-day post-operative mortality and cardiac events. Future studies should determine if treatment of pre-operative anemia and polycythemia improve the post-operative outcomes of this vulnerable population,” they write.
EDITORIAL: HEMATOCRIT LEVEL AND POSTSURGICAL OUTCOME—POWERS OF OBSERVATION
In an accompanying editorial, Farhood Farjah, M.D., and David R. Flum, M.D., M.P.H., of the University of Washington, Seattle, (Dr. Flum is also a Contributing Editor, JAMA), comment on the study by Wu and colleagues.
“How should the unexpected results of this study be interpreted? The most likely explanation for the increased risk of advanced and multiple adenomas in the intervention group is that undetected early precursor lesions were present in the mucosa [a type of membrane] of these patients (who are at increased adenoma risk), and that folic acid promoted growth of these lesions. This hypothesis is consistent with experimental studies showing increased colorectal neoplasia when folic acid is administered after lesions are present.”
“Assuming the relationship of hematocrit and outcome is real and generalizes to other cohorts, the central issue to be determined is whether modifying hematocrit improves outcome. The theory linking preoperative anemia and postoperative events is that the stress of an operation combined with the limited compensatory ability of the heart in older individuals with anemia may lead to cardiac ischemia and death. Interventions correcting anemia aimed at preventing cardiac stress might be expected to save lives, but expectation and reality are often at odds.” They add that several studies did not find important differences in clinical outcomes attributable to blood transfusion for hematocrit levels in the moderate anemia range.
“Since no intervention is without risk, clinicians should avoid using these findings reported by Wu et al to justify interventions—use of transfusion, erythropoietic [of or relating to the formation of red blood cells] agents, iron supplementation—outside the research setting. In other clinical arenas involving patients with anemia, such as those with renal failure and cancer, clinicians may have prematurely embraced the aggressive use of erythropoietic agents to boost red blood cell production in the absence of sufficient evidence, only to learn later that despite their best intentions they may have been causing more harm than benefit,” they write.