Transfusions may raise infection risk for heart surgery patients, particularly women

Updated 10:00 AM January 29, 2007

Transfusions may raise infection risk for heart surgery patients, particularly women

By Kara Gavin
U-M Health System Public Relations

Blood transfusions save the lives of millions of heart surgery patients and others each year. But a new study suggests that patients who receive transfusions during heart bypass surgery have a higher risk of developing potentially dangerous infections and dying after their operations.

In fact, this increased risk may help explain a longstanding medical mystery: why women bypass patients die more often than men in the first few months after surgery. Women are more likely to receive blood during heart bypass operations, which are performed on more than 465,000 Americans each year.

The findings, from the Patient Safety Enhancement Program (PSEP) at the U-M Health System (UMHS), are based on data from 9,218 Michigan bypass patients. After adjusting for factors such as the urgency of the operation, those who received blood transfusions from donors were five times more likely to die within 100 days of their operation than those who did not.

The paper is published in the December issue of the American Heart Journal. It builds on a previous U-M analysis that found a difference in infection rates accounted for the difference in death risk between men and women bypass patients.

The U-M team, with the help of Dr. Neil Blumberg of the University of Rochester Medical Center, focused on blood transfusions as a contributing factor. Prior research has shown that recipients of stored donor blood have more post-surgical infections, and that women receive more transfusions because they tend to have lower hemoglobin concentrations.

This new study connects the dots. "To the best of our knowledge, this is the first study to state that allogeneic transfusions may be the reason why women have a greater post-bypass surgery mortality risk than men," says author Mary A.M. Rogers, research director and research assistant professor of internal medicine. Allogeneic is the term for blood from another person.

The study is based on analysis of data from all Medicare beneficiaries ages 65 and older who had coronary artery bypass operations in Michigan in a single year.

The researchers performed statistical analyses that took into account the patients' blood transfusion status, their co-existing diseases, age, race, sex, and whether the bypass operation was done on an elective, urgent or emergency basis. They looked at infections and deaths that were reported during the 100 days after surgery.

In all, about 88 percent of women received an allogeneic blood transfusion during bypass surgery, compared with nearly 67 percent of men. When the researchers adjusted for other factors, women were 3.4 times as likely as men to receive blood. This gender difference was evident regardless of whether the operation was elective, urgent or an emergency.

The odds of having an infection of any kind were about three times greater in patients who received allogeneic blood than in patients who did not. The more blood they received, the higher their infection risk.

No single type of infection stood out as more common among blood recipients, which suggests a body-wide immune response issue rather than a problem, for example, at the site of the incision.

The analyses revealed that women were more likely to experience an infection than men after bypass surgery, which appeared to be due to the increased number of transfusions in women. This resulted in an increased mortality rate in women. Overall, 9 percent of women and 6 percent of the men died within 100 days of their operation.

For patients who had banked their own blood ahead of the operation and who received only their own blood, the infection risk was similar to that of patients who received no blood transfusions.

The authors strongly note that blood transfusions can be life saving, and that the infections observed in this study are not likely due to contamination of the blood. Rather, they may be due to other factors, including the patient's immune response to substances such as white blood cells that are present in stored donor blood. These findings may help guide hospitals and blood banks in deciding whether to filter donated blood to reduce the levels of white blood cells. This practice is increasingly common, but not yet universal, in the United States.

The results also highlight the importance of the proper use of antibiotics and infection control practices in patients hospitalized for a surgical procedure, Rogers says.

The team is investigating the issue further, including a new study funded by Blue Cross Blue Shield of Michigan Foundation to extend the research into elderly patients who recently underwent bypass surgeries in Michigan.

In addition to Rogers and Blumberg, the study authors included PSEP director Dr. Sanjay Saint, Dr. Catherine Kim, Dr. Brahmajee Nallamothu and Dr. Kenneth Langa. It was funded by the Agency for Healthcare Research and Quality, the National Institutes of Health, the Department of Veterans Affairs, the John A. Hartford Foundation and a Paul B. Beeson Physician Faculty Scholars in Aging Research award.

Transfusions may raise infection risk for heart surgery patients, particularly women

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