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

BACKGROUND: Approximately 20 percent of all allogeneic blood transfusions are administered in connection with coronary artery bypass graft (CABG) operations. Transfusion practices vary across the country. The whole-body oxygen 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 being shown to be an appropriate transfusion trigger. The present study monitored the O 2 ER in patients undergoing CABG and determined if transfusion practices would have been different if an O 2 ER ≥45 percent were used as a transfusion trigger. STUDY DESIGN AND METHODS: Seventy patients with a postoperative Hct ≤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 transfusion. These patients were older, weighed less, and had a preoperative Hct lower than the nontransfused patients. There were no significant differences between transfused and nontransfused patients with respect to postoperative 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 the transfusion group, 7 of 21 patients had a postoperative O 2 ER >45 percent, while 3 of 35 in the nontransfused group had that result. CONCLUSION: The use of O 2 ER as a transfusion trigger as part of a transfusion algorithm could lead to a reduction in allogeneic blood transfusion.