Abstract: Objective: To analyze the relationship between the ratio of difference of venous-arterial blood carbon dioxide differential pressure(Pv-aCO₂) to difference of arterial-venous blood oxygen content(Ca-vO₂)(Pv-aCO₂/Ca-vO₂) and lactic acid clearance in cardiac surgery patients after cardiopulmonary bypass,and evaluate its therapy value. Methods: A total of 119 CPB post-cardiac patients were selected,the central vein and arterial blood gas analysis at the time of transferring to ICU and after 3 h of surgery were detected,and the corresponding Pv-aCO₂/Ca-vO₂ ratio was calculated.The general conditions,hemodynamic indexes,oxygen metabolism indexes,lactic acid,peripheral perfusion index(PI),SOFA score and vasoactive drug dose were collected to calculate the 3 h lactate clearance rate(LCR).According to the 3 h LCR,the patients were divided into the LCR<10% group(21 cases) and LCR≥10% group(98 cases).The hemodynamic indexes,oxygen metabolism indexes,PI,PPV and Pv-aCO₂/Ca-vO₂ were compared between two groups. Results: There was no statistical significance in the gender,body temperature,SOFA score,PH,PI,PPV,hemoglobin,norepinephrine,epinephrine dose and hemodynamic parameters between two groups(P>0.05).At the time of transferring to ICU,the Pv-aCO₂/Ca-vO₂ in the LCR≥10% group was lower than that in LCR<10%(P<0.05).After 3 h of surgery,the lactic acid in the LCR≥10% group was significantly lower than that in LCR<10%(P<0.01). Conclusions: After CPB cardiac surgery,the Pv-aCO₂/Ca-vO₂ can be used to assist the guidance of postoperative lactic acid clearance,and the lower level of Pv-aCO₂/Ca-vO₂ is conducive to postoperative lactic acid clearance.