BALTIMORE — A low hemoglobin level following cardiac surgery is associated with significantly increased odds of experiencing a stroke after cardiopulmonary bypass, results of a case-control study suggest.
Although previous studies have associated anemia with adverse cerebrovascular outcomes, including stroke, it is unclear whether low hemoglobin levels contribute to postoperative surgical complications, Dr. Rebecca F. Gottesman and her colleagues at Johns Hopkins University, Baltimore, said in a poster presented at the annual meeting of the American Neurological Association.
The researchers identified the postoperative outcomes of 357 patients who underwent various cardiac surgery procedures with cardiopulmonary bypass at Johns Hopkins Hospital and compared them with the outcomes of 714 control patients matched by age range, gender, and type and year of surgery.
The patients had a mean age of 65 years, and 59% in each group were male. Compared with controls, stroke patients were significantly more likely to have hypertension (77% vs. 68%) and peripheral vascular disease (20% vs. 10%). The stroke and control groups had similar rates of diabetes mellitus (30% vs. 25%, respectively), history of myocardial infarction (37% vs. 32%), and high cholesterol (51% vs. 45%).
In a conditional logistic regression analysis, the investigators found that, for each 1 g/dL decline in hemoglobin, the odds of having a stroke significantly increased by 37%. Patients with a postoperative hemoglobin level below the group median of 8.8 g/dL had a 78% greater chance of having a stroke than did those above the median. (Normal hemoglobin levels are greater than 13 g/dL in men and greater than 12 g/dL in women.)
Postoperative hemoglobin levels were below the median in significantly more patients who had a new stroke (57%) than in those who did not have a stroke (41%).
“The association between stroke and post-cardiopulmonary bypass hemoglobin could be the result of hemodilution or cerebral hypoperfusion,” Dr. Gottesman and her associates suggested. Studies are needed to determine whether having normal hemoglobin levels would decrease the risk of stroke.
The study was supported by grants from the National Institutes of Health and the Dana Foundation.