Category :Endocrine disease A168-Central venous-arterial pco2 difference to arterio-venous oxygen content difference ratio, pcv- aco2/ca-cvo2, in patients with metformin associated lactic acidosis (mala): a marker of anaerobic metabolism?

Introduction: A growing interest exists about CO2 derived parameters in shock management. Central venous-arterial pCO2 difference (pcv-aCO2) is strictly related to cardiac output; central venous-arterial pCO2 difference to arterialcentral venous O2 content difference ratio, pcv-aCO2/Ca-cvO2, has been proposed as anaerobic metabolism when it’s >1,4 mmHg/ml[1]. Methods: To evaluate pcv-aCO2/Ca-cvO2 reliability in detecting anaerobic metabolism, we analyzed it in 7 consecutive patients affected by MALA admitted to our ICU, considering these patients as a prevalent anaerobic metabolism model. We calculated, by Douglas formula, central venous-arterial CO2 content difference to arterial-central venous O2 content difference ratio, Ccv-CaCO2/Ca-CcvO2, as a Respiratory Quotient surrogate. We performed arterial and central venous blood gas analysis simultaneously at admission, we calculated pcvaCO2, pcv-aCO2/Ca-cvO2 and Ccv-aCO2/Ca-cvO2 and we recorded ScvO2. We verified relationship between pcvaCO2/Ca-cvO2 and ScvO2 and arterial pH, arterial lactates, SOFA score at admission and Ccv-aCO2/Ca-cvO2 by linear regression analysis. Results: pcv-aCO2/Ca-cvO2 greatly increases in MALA (2,16 ± 0,84). pcv-aCO2/Ca-cvO2 (fig.1) shows significant co-variation with pH (R2=0,618; p=0,003) and SOFA score at admission (R2=0,628; p=0,003). pcv-aCO2/Ca-cvO2 has poor agreement with Ccv-aCO2/Ca-cvO2 (R 2=0.008) and disagrees with it in identifying anaerobic metabolism, in our series, in fact, Ccv-aCO2/Ca-cvO2 is, in 3 patients, < 1 like an aerobic RQ value. pcv-aCO2/Ca-cvO2 shows better agreement with pH, SOFA score and lactate level than ScvO2. Conclusion: In our series, pcv-aCO2/Ca-cvO2 is good illness and acidosis severity marker, but it seems to be affected by pH value in accord with Haldane effect [2]. pcv-aCO2/Ca-cvO2, in our study, doesn’t seem to be a reliable anaerobic metabolism marker nor a RQ surrogate. References: [1] Mekontso-Dessap A et al Intensive Care Med 28:272-277, 2002. [2]Teboul JL et al Intensive Care Med 43(1):91-93, 2016