Objective:To determine factors influencing the individual effects of blood transfusions regarding oxygen delivery and consumption.Design:Chart review.Setting:A university hospital cardiosurgical intensive care unit.Patients:Sixty-seven patients with 170 transfusion events evaluated.Interventions:Blood transfusion.Measurements and Main Results:Measurements were performed before and after a blood transfusion, separated by 302 ± 13 mins (mean ± SEM). The individual increase in cardiac index resulting from a blood transfusion was inversely related to cardiac index before transfusion (p< .001), oxygen delivery index before transfusion (p< .001), and oxygen consumption index before transfusion (p< .001). The individual increase in oxygen delivery index was inversely related to oxygen consumption index before transfusion (p< .001). The individual increase in oxygen consumption index was inversely related to oxygen consumption index before transfusion (p< .001). Individual changes in cardiac index, oxygen delivery index, and oxygen consumption index were not significantly related to preoperative ejection fraction (25%-87%), age (32-81 yrs), and pretransfusion hemoglobin concentration (5.0-11.8 g/dL).Conclusion:In adult patients after cardiovascular surgery, oxygen delivery- and oxygen consumption-related variables predict the individual response to blood transfusions better than do patient characteristics such as preoperative ejection fraction, age, and pretransfusion hemoglobin concentration. Including oxygen delivery and oxygen consumption, variables into the transfusion decision, thus, may enable a more individual use of allogeneic blood in specific situations.