Evaluation of the quotient of the venoarterial carbon dioxide gradient and the arteriovenous oxygen content difference as a transfusion trigger parameter in hemodynamically stable patients with significant anemia

Abstract

Introduction Hemoglobin as the main trigger parameter for blood transfusion usually gives diminutive information about oxygen delivery and consumption. Although central venous oxygen saturation (ScvO2 ) is an alternative parameter, its changes are unable to detect regional hypoxia. Our aim was to evaluate the quotient of the central venous-toarterial carbon dioxide gradient ($δ$PCO2 ) and the arteriovenous oxygen content difference (Ca-cvO2 ) as a valid transfusion trigger parameter in hemodynamically stable anemic patients to reduce the amount of potentially counterproductive erythrocyte transfusions [1]. Methods Forty-five postoperative patients admitted to our cardiac ICU were enrolled between January 2013 and September 2014. Three groups were defined according to the trend of blood loss over the surgical drains in the first 24 postoperative hours. Mild blood loss was defined as 500 to 1,000 ml/24 hours, moderate (1,000 to 1,500/24 hours) and severe (>1,500 ml/24 hours). In addition to the $δ$PCO2 the following parameters were monitored: CI, CO, SVR, serum lactate, ScvO2 and hemoglobin. Ca-cvO2 was calculated and the $δ$PCO2 / Ca-cvO2 quotient was assessed for a total of 400 paired blood samples. All enrolled patients were hemodynamically stable. A retrospective analysis of this data was performed. Results $δ$PCO2 /Ca-cvO2 showed significant correlation with the moderate and severe blood loss groups (P <0.01), while no significant correlation was detected in the mild blood loss group. The abnormality of the $δ$PCO2 /Ca-cvO2 was easy detectable and reflected intracapillary hemoglobin capacity decline and significantly improved after erythrocyte transfusions (P <0.005). Conclusion Blood transfusions carry risks of adverse effects and should be carried out responsibly. Our findings suggest an additive and easy detectable transfusion trigger parameter ($δ$PCO2 /Ca-cvO2 ) providing physiological information on anemia-related altered oxygen extraction conditions and hence the indication for erythrocyte transfusions. However, additional studies are warranted to confirm these findings.