Model Helps Clinicians Predict Post-Cardiac Surgery Blood Transfusions

While lifesaving in some circumstances, a blood transfusion can add new problems for patients undergoing cardiac surgery, including an increased risk of death.

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To combat this, a recent study explored which risk factors might make some cardiac surgery patients more likely to require a red blood cell transfusion associated with the procedure to help physicians plan ahead.

"Few studies have focused on identifying patients who are at risk of needing blood," says Donald Likosky, Ph.D., associate professor of cardiac surgery at the University of Michigan Medical School and first author on the Annals of Thoracic Surgery article. "If surgical teams could make an accurate assessment of risk for each patient, targeted efforts could be applied to mitigate that patient's risk of needing blood products."

Lifesaving but risky

Red blood cell transfusions, given during or after the procedure, are necessary to save the lives of some patients, including those requiring large quantities of blood to address severe bleeding.

But even the smallest quantities of blood transfusions are associated with a higher risk of major morbidity and death. A 2014 study Likosky co-authored found just one or two units of red blood cells significantly increased morbidity and mortality among patients undergoing coronary artery bypass grafting (CABG).

Investigators have previously developed prediction models for blood transfusions in this setting. Unfortunately, most of these studies have included a mixture of surgical procedures. To address this limitation, Likosky and colleagues focused specifically on patients undergoing CABG.

"Applying the conclusions to just one procedure instead of all cardiac surgeries improves the performance of our model," says Likosky, also a member of U-M's Institute for Healthcare Policy and Innovation.

The study team evaluated 20,377 patients who underwent isolated coronary artery bypass grafting at hospitals across Michigan that contribute data to the Perfusion Measures and outcomes Registry, which is housed at the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative. The data shared with the quality collaborative have already led to important findings that help drive targeted improvement in clinical practice, including a previous U-M-led report on the risk for pneumonia after cardiac surgery.

What drives transfusion need

The study reports 16 preoperative variables, though four had the strongest associations to the need for transfusion in CABG patients:

1. Smaller body size (especially body surface area less than 1.8 square meters)

2. Emergency surgery

3. Dialysis at the time of the operation

4. Low proportion of red blood cells (low hematocrit levels)

Other variables associated with higher odds of transfusion include three-vessel disease, total albumin, previous cardiovascular procedure and congestive heart failure.

SEE ALSO: To Fight Pneumonia After Cardiac Surgery, Data Could Be the Weapon

The model performed well across subgroups including age, sex and medical center.

"Our model serves as the foundation for more informed decision-making prior to surgery. Clinicians using our model may now have a better idea of which CABG patients would potentially benefit from pre- or intraoperative blood management strategies," says Gaetano Paone, M.D., senior author with Henry Ford Health System.

Along with Likosky and the U-M team, co-authors include cardiac surgery colleagues from facilities across Michigan, such as Henry Ford Hospital and Bronson Methodist Hospital, and one author at the Mayo Clinic in Minnesota.

This project was funded in part by grant number R03HS022909 from the Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services. The opinions expressed in this document are those of the authors and do not reflect the official position of the AHRQ or HHS.

Support for the MSTCVS Quality Collaborative is provided by Blue Cross Blue Shield of Michigan and Blue Care Network as part of the BCBSM Value Partnerships program.