Effect of Red Blood Cell Transfusion on Central Venous-to-Arterial Carbon Dioxide Difference in Anemic Surgical Patients – A Pilot Study

Background: Biochemical markers for monitoring adequacy of cardiac output and tissue perfusion such as blood lactate and central venous oxygen saturation (ScvO2) are meanwhile well established in clinical routine. In addition, in recent years, the central venous-to-arterial carbon dioxide difference (dCO2) has been evaluated as a further marker, and studies meanwhile have demonstrated the validity of an increased dCO2 to identify capillary perfusion mismatches. However, results from animal studies suggest that dCO2 may be influenced by altered hemoglobin values during severe bleeding. It was the aim of our study to evaluate if dCO2 changes upon Red Blood Cell (RBC) transfusion in humans. Methods: Patients of the ongoing LIBERAL trial were prospectively evaluated. Participants were aged ≥70 years and scheduled for elective intermediate or high risk orthopedic or trauma surgery with the clinical need for invasive blood pressure monitoring and central venous catheterization. During surgery, drop of hemoglobin triggered administration of one single RBC unit, together with arterial and central venous blood analysis immediately before as well as after transfusion. Results: In total, 46 patients were analyzed. Baseline median hemoglobin before RBC transfusion was 8.35 (7.48–8.73)g/dl, while dCO2 was 6.2 (3.4–9.6)mmHg. According to Spearman correlation, there was a linear association between pre-transfusion dCO2 and ScvO2. Transfusion of one RBC unit resulted in a significant increase of median hemoglobin by 1.2 (0.7–1.63)g/dl (p<0.0001), and hemoglobin increase was more pronounced when pre-transfusion hemoglobin was low, as evidenced by a significant negative association between both parameters (r=-0.61, p <0.0001). Neither lactate nor ScvO2 nor dCO2 were significantly influenced by transfusion. When the whole cohort was divided according to pre-transfusion dCO2 levels using a cut-off value of 6 mmHg, median dCO2 decreased significantly more pronounced following RBC transfusion when pre-transfusion values were high (>6 mmHg), compared to those patients with a pre-transfusion dCO2 below 6 mmHg. Conclusions: The results of our study suggest that crude dCO2 is not influenced by moderate hemoglobin increases in orthopedic and trauma surgery patients. However, including dCO2 into the decision whether to administer RBC or not may be an interesting reasonable approach for further investigations on the way towards more individualized transfusion regimens.