Toronto-led study to change transfusion practices around the world

A global study led by Toronto researchers is expected to change transfusion practices for cardiac surgery around the world to make more blood available, reduce costs and lead to similar or better outcomes. The study is published in the New England Journal of Medicine.

Lower thresholds for blood transfusions for cardiac surgery patients compared to traditional thresholds provide positive patient outcomes and safety at six months after surgery, according to the world’s largest research study on this topic.

The research found that in addition to providing good patient outcomes six months after hospital discharge, the lower threshold - known as ‘restrictive transfusion therapy’ - reduces the amount of blood transfused and money spent on blood per procedure. The higher, traditional threshold is called ‘liberal transfusion therapy.’

Physicians who practice the liberal transfusion approach give blood transfusions early in the surgery to prevent patients’ hemoglobin level from falling. Hemoglobin is the protein that allows red blood cells to deliver oxygen to body tissues. Physicians who practice a restrictive approach wait longer to see if the hemoglobin level remains stable or if the patient has further bleeding.

These findings were presented at the European Society of Cardiology Annual Congress in Munich, Germany by principal investigator David Mazer, a professor in the Departments of Anesthesia and Physiology. Mazer is also an anesthesiologist at St. Michael’s Hospitaland an associate scientist in its Keenan Research Centre for Biomedical Science.

“Our research question was, at what point does the risk of anemia, or the risk of a lower hemoglobin, outweigh the risk of transfusion?” Mazer said. “We wanted to know whether it is safe to let your hemoglobin go to a lower level before you transfuse. The answer is yes. It'll save blood, make blood more available, reduce costs of transfusion and result in similar or better outcomes."

This work builds on Mazer’s research published less than a year ago in the New England Journal of Medicine, which analyzed immediate postoperative patient outcomes. The randomized trial involved more than 5,200 patients at 74 sites in 19 countries and every continent in the world except Antarctica. At the six-month mark, data was available for 96 per cent of the patients.

Mazer co-led the study with Nadine Shehata, a professor in the Department of Laboratory Medicine and Pathobiology and hematologist at the Sinai Health System. The research team found no clinical or statistical difference in four patient outcomes (death, heart attack, stroke and new kidney failure), whether the patients had contemporary restrictive therapy or traditional liberal practices. In fact, use of the restrictive transfusion protocol during and after heart surgery may actually reduce the incidence of complications in older patients, including heart attack, stroke, kidney failure and death.

“This research has already started to change transfusion practice around the world,” said Mazer. “With this data at six months, we’ve proven the longer term safety of restrictive therapy. This approach has already been adopted into guidelines and will likely become the standard of care worldwide.”

The large size of this study provides Mazer and his team additional opportunity to answer several other important questions related to transfusion and cardiac surgery.

This study received funding from the Canadian Institutes of Heart Research, Canadian Blood Services, the National Health and Medical Research Council in Australia and the Health Research Council of New Zealand.