THE PARADOX OF ON-BYPASS TRANSFUSION THRESHOLDS IN BLOOD CONSERVATION

Background While most reports on blood conservation define a specific transfusion trigger, few have primarily focused on the role of the pre defined transfusion threshold in initiating blood utilization. This st udy was undertaken to test the hypothesis that rigid adherence to an a rbitrarily defined protocol paradoxically increases homologous blood u sage during isolated primary coronary artery bypass graft. Methods and Results Prospectively, 100 consecutive patients were transfused on by pass solely for low venous oxygen saturation (Svo(2)), ie, <55%, witho ut regard to hematocrit (Hct), postoperative for Hct <20, or if clinic ally warranted. During bypass the lowest Hct value was <25% in 72 pati ents, <22% in 52 patients, <20% in 39 patients, <18% in 23 patients, a nd <15% in 2 patients. These data, then, represent the percentage of p atients who would have received blood on bypass had each respective le vel been used as a trigger, and hence the minimum number of patients w ho would have been transfused overall. In this study only 13 patients received 2.2+/-0.3 U of red blood cells; 4 on bypass, 5 in the intensi ve care unit within 24 hours, and 4 on postoperative days 2 or 3. Of t he 87 patients not transfused, 15 arrived in the intensive care unit w ith Hct <25%, 4 with Hct <22%. By postoperative day 1, there were 7 pa tients with Hct <25% and only 1 <22%, confirming that many of these pa tients would have been unnecessarily transfused had we adhered to any of the noted on-bypass transfusion triggers. There were no deaths, no strokes, one Q wave myocardial infarction, and one sternal infection. Postoperative blood loss and discharge Hct were 741+/-131 mt and 29.3/-0.5 versus 573+/-27 mt and 29.1+/-1.0 in transfused and nontransfuse d patients (P=.24 and P=.88, respectively). Conclusion These data sugg est that avoiding use of a numerical on-bypass hematocrit trigger is s afe and extremely effective in minimizing the use of homologous blood during isolated primary coronary artery bypass graft. Conversely, unle ss the chosen level is sufficiently low, ie, <15, setting arbitrary th resholds will paradoxically increase homologous blood utilization; dat a are mean+/-SEM.