Evaluation of oxygen extraction ratio as a physiologic transfusion triggerin coronary artery bypass graft surgery patients

BACKGROUND: Approximately 20 percent of all allogeneic blood transfusions a re administered in connection with coronary artery bypass graft (CABG) oper ations. Transfusion practices vary across the country. The whole-body oxyge n extraction ratio (O-2 ER) reflects the adequacy of the patient's response to acute normovolemic anemia with an O-2 ER of approximately 50 percent be ing shown to be an appropriate transfusion trigger. The present study monit ored the O-2 ER in patients undergoing CABG and determined if transfusion p ractices would have been different if an O-2 ER greater than or equal to 45 percent were used as a transfusion trigger. STUDY DESIGN AND METHODS: Seventy patients with a postoperative Hct less th an or equal to 25 percent were the test subjects. Arterial and mixed venous contents were determined before the operation. in the intensive care unit after the operation, and 12 hours after the operation. RESULTS: There were no deaths. Forty-one patients received allogeneic trans fusion. These patients were older, weighed less, and had a preoperative Hct lower than the nontransfused patients. There were no significant differenc es between transfused and nontransfused patients with respect to postoperat ive Hct (21.0 +/- 0.4 vs. 22.2 +/- 0.4), cardiac index (2.5 +/- 0.1 vs. 2.7 +/- 0.1), O-2 delivery (6.4 +/- 0.3 vs. 6.7 +/- 0.3), O-2 consumption (2.5 +/- 0.1 vs. 2.5 +/- 0.1), and O-2 ER (38.3 +/- 1.7 vs. 37.5 +/- 1.5). In t he transfusion group, 7 of 21 patients had a postoperative O-2 ER greater t han or equal to 45 percent, while 3 of 35 in the nontransfused group had th at result. CONCLUSION: The use of O-2 ER as a transfusion trigger as part of a transfu sion algorithm could lead to a reduction in allogeneic blood transfusion.