Central venous oxygen saturation is a good indicator of altered oxygen balance in isovolemic anemia.

ABSTRACT

BACKGROUND: Red blood cell transfusion is done primarily as a means to improve oxygen delivery (DO2). Current transfusion guidelines are based solely on hemoglobin levels, regardless of actual DO2 need. As central venous oxygen saturation (ScvO2) may reflect imbalances in DO2 and consumption (VO2) the aim of this study was to investigate the value of ScvO2 as an indicator of oxygen balance in isovolemic anemia. METHODS: After splenectomy, anesthetized Vietnamese mini pigs (n = 13, weight range 18-30 kg) underwent controlled bleeding in five stages (T0-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. RESULTS: Each stage of bleeding resulted in a significant fall in hemoglobin, T0 125 (113-134) to T(5) 49 (43-55) g/l [T0 7.7 (6.9-8.2) to T5 3.0 (2.6-3.4) mmol/l]. The O2-extraction (VO2/DO2) increased significantly only from T3 35 (21-40) %, P < 0.05. The change of ScvO2 showed a similar pattern and dropped below the physiological threshold of 70% at T4 68 (61-76) %. At this point, hemoglobin was below the recommended transfusion trigger value, 59 (53-67) g/l [3.6 (3.3-4.1) mmol/l]. There was a strong significant association between ScvO2< 70%) and VO2/DO2 > 30%) r = -0.71, r² = 0.50, P < 0.001. CONCLUSION: The results of this study show that ScvO2 reflects changes of VO2/DO2 in isovolemic anemia better than Hb alone, therefore it may be used as an additional indicator of blood transfusion in clinical practice.