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 (O2 ER) reflects the adequacy of the patient's response to acute normovo‐lemic anemia with an O2 ER of approximately 50 percent being shown to be an appropriate transfusion trigger. The present study monitored the O2 ER in patients undergoing CABG and determined if transfusion practices would have been different if an O2 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), O2 delivery (6.4 ± 0.3 vs. 6.7 ± 0.3), O2 consumption (2.5 ± 0.1 vs. 2.5 ± 0.1), and O2 ER (38.3 ± 1.7 vs. 37.5 ± 1.5). In the transfusion group, 7 of 21 patients had a postoperative O2 ER ≥45 percent, while 3 of 35 in the nontransfused group had that result. CONCLUSION: The use of O2 ER as a transfusion trigger as part of a transfusion algorithm could lead to a reduction in allogeneic blood transfusion.