Clinical Value Of Pv-aCO₂ In Volume Management Post OPCAB

Objective To investigate whether mixed venous to arterial carbon dioxide difference（Pv-a CO₂）combined with passive leg raising（PLR）could be a better method of guiding volume management than CVP,and discuss the clinical values of Pv-a CO₂ in patients post off-pump coronary artery bypass（OPCAB）.Methods From June 1st to October 1st,patients post OPCAB in Tianjin Chest Hospital were enrolled.Inclusion criteria:（1）selective OPCAB.（2）left ventricular ejection fraction of preoperation ≥40%.（3）Applying Swan-Ganz catheter to monitor the hemodynamic parameters.Exclusion criteria:（1）serious lung diseases,liver and kidney dysfunction.（2）emergency operation.（3）severe valvular stenosis and-or regurgitation.（4）second operation for CABG.（5）BMI>30Kg/m2.（6）refused to participate in this study.Rejection criteria:（1）re-exploring hemostasis.（2）died within 24 hours.（3）IABP assist.（4）failure placement of Swan-Ganz catheter.All of them were monitored ECG,invasive arterial blood pressure,and cardiac output and were given ventilation immediately after admission to ICU.They were given corresponding volume management.（1）Collected artery and mixed venous blood gas results and hemodynamic parameters at 0h,6h after admission to ICU,compared T,HR,MAP,CVP,Pv-a CO₂,Sv O₂,lactate,Pa O₂/Fi O₂,fluid intake of 6h,scores of vasoactive agents,duration of mechanical ventilation and ICU,length of stay between two groups.（2）According to HR,MAP,PP,CVP,PAWP,Sv O₂,Pv-a CO₂,CI of before and after PLR,analyzed the correlation between △CI and △Pv-a CO₂.（3）Analyzed the correlation between Pv-a CO₂ and CI,SVO₂,Lac in observation group.（4）The mean values of every time point of Pv-a CO₂ of the two groups at 0h,6h,24 h after admission to ICU were calculated,and the correlation between Pv-a CO₂ and prognosis were analyzed.Results 91 patients were include in this study,excluding 11 cases,and ultimately 80 patients including 60 male and 20 female were randomly divided into two groups,observation group（40 cases）given Pv-a CO₂ combined with PLR to direct therapy and control group（40 cases）given central venous pressure（CVP）direct therapy.Between the two groups,there were no statistical difference in general data,admission ICU 0h parameters of hemodynamic,tissue and oxygenation.（1）At 6h post operation,the Sv O₂ and fluid intake in observation group were higher than those in control group（P<0.05）.The Pv-a CO₂,Lac and scores of vasoactive agents in observation group were lower than those in control group（P <0.05）.Duration of mechanical ventilation and ICU in the observation group were less than those in the control group（P<0.05）.（2）In observation group,PLR were applied on 35 patients,volume responsiveness in 24 cases and non volume responsiveness in 11 cases.Before and after PLR,changes of HR,MAP,PP,CVP and PAWP have no statistical difference（P>0.05）.The increase of CI,Sv O₂ and decrease of Pv-a CO₂ induced by PLR had statistical difference.There are significant negative correlation between changes of CI and Pv-a CO₂ induced by PLR（r=0.684,P<0.05）.Take the changes of Pv-a CO₂ induced by PLR as test variable,take the changes of CI induced by volume challenge as state variable,and the area under ROC curve is 0.793.The sensitivity and specificity was 95% and 73% respectively to judge the volume responsiveness.（3）Pv-a CO₂ had significant negative correlation with CI,low negative correlation with Sv O₂ and no correlation with Lac,and all have significant difference（r=-0.752,r=-0.154,r=-0.314,P<0.05）.（4）The peak value of Pv-a CO₂ was observed at 0h after ICU admission among the 80 patients,and analyze the correlation between Pv-a CO₂ and prognosis: duration of mechanical ventilation and ICU,length of stay were longer,and SOFA scores were less in the group of Pv-a CO₂≥6mm Hg than those in the group of Pv-a CO₂ ≤6mm Hg.But all of them have no significant difference（P>0.05）.Conclusion（1）Pv-aCO₂ combined with PLR can better guide volume management than CVP in the patients post OPCAB.（2）Changes in Pv-a CO₂ induced by PLR can judge volume responsiveness.（3）Pv-a CO₂ had strong negative correlation with CI,low negative correlation with Sv O₂,and no correlation with Lac.（4）High Pv-a CO₂ can not predict worst outcome in post OPCAB patients.