The value of oxygen-carrying solutions in the operative setting, as determined by mathematical modeling

BACKGROUND: The use of oxygen carriers (red cell [RBC] substitutes) in acut e trauma and in surgery, with or without the use of acute normovolemic hemo dilution (ANH), is being investigated. Mathematical modeling was used to as sess the impact of RBC substitutes with or without ANH, in the elective sur gical setting. STUDY DESIGN AND METHODS: Mathematical equations and computer models were d eveloped on the basis of previously described mathematical principles, for better understanding of the potential efficacy of RBC substitutes for blood needs with or without ANH. Savings were calculated for a patient with a bl ood volume of 5000 mt and an initial hematocrit (Hct) of 45 or 30 percent RESULTS: Substantial increases in the tolerable blood losses (or reduced al logeneic RBC needs) were most evident when the use of an RBC substitute to achieve severe ANH to a Hct that the patient might not otherwise have been able to tolerate was combined with the use of RBC substitutes as replacemen t for the surgical blood subsequently lost. However, the benefit was greatl y dependent on the patient's initial Hot. For example, for a patient with a blood volume of 5000 mt and an initial Hct of 45 percent, a blood loss of approximately 2500 mt resulted in a find Hct of 28 percent without the use of an RBC substitute or ANH. In contrast, with the combined use of staged A NH with an RBC substitute and the RBC substitute for lost surgical Mood, a blood loss of up to 14.5 L could be tolerated. However, in an anemic patien t (Mood volume 5000 mt, initial Hct 30%), a Hct of 28 percent cannot be sus tained without the use of allogeneic RBCs for any of the described strategi es, even when blood losses were as low as 1 L. CONCLUSION: The use of RBC substitutes has the potential to result in a sub stantial reduction in allogeneic RBC exposure. This benefit is essentially limited to the nonanemic patient when the use of an RBC substitute is combi ned with severe ANH and there is concomitant large perioperative Mood loss. Anemic patients can be expected to have only limited benefit, because of a n inability to sequester an adequate volume of autologous RBCs via ANH.