 This proposal aims to provide some objective, non-invasively achieved, physiologically relevant data in order to provide some rational basis for decision-making for transfusion in sTBI. Specifically this proposal is an observational study of transfusion and brain tissue saturation in sTBI patients. The results will illustrate to what degree brain tissue oxygenation is critically dependent on the degree of anemia in sTBI and help in the decision of whether transfusion might be helpful. 