Transfusion thresholds in cardiac surgery: Commentary on Bracey et al., 1999

Approximately 25 years ago, the standard of care was to transfuse patients whenever the hemoglobin (Hgb) level fell below 10 g/dl and the hematocrit (Hct) below 30% (the “10/30 rule”). Remarkably, this recommendation was based largely on opinions expressed in the 1940s. In 1988, an NIH consensus conference on peri-operative red blood cell transfusions concluded that there was no evidence to support a single criterion such as the “10/30” rule. At the same time, there were increasing concerns about the safety of the blood supply, especially with respect to HIV and hepatitis. Therefore, many guidelines were developed with the emphasis on avoiding red blood cell transfusions with less consideration of the consequences of withholding transfusion. The NIH consensus conference highlighted the dearth of evidence and stimulated the conduct of trials evaluating transfusion thresholds. These trials are often called “trigger” trials, where a specified hemoglobin concentration “triggers” transfusion. These trials compare a higher hemoglobin level to a lower transfusion threshold, often referred to as liberal transfusion and restrictive transfusion, respectively. In October 1999, Art Bracey and colleagues published one of the earliest transfusion trigger trials in the journal TRANSFUSION. The trial enrolled 428 patients undergoing elective primary coronary artery bypass surgery at the Texas Heart Institute, which was one of the leading cardiac surgery centers. Trial enrollment was initiated in February 1997 and completed in just over 9 months in this single-center study. The manuscript was submitted for publication in October 1998, and the revision was published 1 year later. The widely cited TRICC trial was published in February 1999—just 8 months before Bracey's trial—and was conducted in 25 ICUs and it took 3 years to enroll 838 critically ill patients. Five smaller trials were published prior to these classic studies, including the pilot study for TRICC.6–11 In the Bracey trial, cardiac surgical patients were randomly assigned to be transfused postoperatively for a Hgb concentration below 8 g/dl or below 9 g/dl. The outcomes assessed included in-hospital mortality, morbidity, blood use, length of hospital stay, length of ICU stay, and selfassessment of fatigue. Of the 428 patients enrolled, only 149 of the patients had postoperative Hgb levels of less than 9 g/dl. The 8 g/dl transfusion arm received 20% fewer RBC units, although the lowest Hgb throughout the hospitalization was similar. There were no differences in clinical outcomes except for better Day 5 fatigue scores in the 9 g/dl arm. However, the authors interpreted the results as not showing significant differences after further analyses. Since the Bracey study, transfusion thresholds have been evaluated in six additional trials in patients undergoing coronary artery bypass surgery. These trials have applied different criteria in protocols, including the Received: 5 October 2022 Accepted: 5 October 2022