Despite
blood transfusions are administered to restore adequate tissue oxygenation, transfusion guidelines consider only
hemoglobin as trigger value, which gives little information about the balance between
oxygen delivery and consumption. Central venous oxygen saturation is an alternative, however its changes reflect systemic metabolism and fail to detect regional
hypoxia. A complementary parameter to ScvO2 may be central venous-to-arterial
carbon dioxide difference (CO2-gap). Our aim was to investigate the change of alternative transfusion trigger values in experimental isovolemic
anemia. After
splenectomy, anesthetized Vietnamese mini pigs (n = 13, weight range: 18-30 kg) underwent controlled
bleeding in five stages (T1-T5). During each stage approximately 10% of the estimated starting total blood volume was removed and immediately replaced with an equal volume of
colloid. Hemodynamic measurements and blood gas analysis were then performed. Each stage of
bleeding resulted in a significant fall in
hemoglobin, the O2-extraction increased significantly from T3 and ScvO2 showed a similar pattern and dropped below the physiological threshold of 70% at T4. By T4 CO2-gap increased significantly and well correlated with VO2/DO2 and ScvO2. To our knowledge, this is the first study to show that
anemia caused altered
oxygen extraction may have an effect on CO2-gap.