Comparison of venous pCO2 and exhaust pCO2 for calculating CO2 production during cardiopulmonary bypass

Introduction Carbon dioxide production (VCO2i), oxygen consumption and oxygen delivery can be monitored during cardiopulmonary bypass (CPB) as markers for tissue perfusion. This study examines if inline venous pCO2 (PvCO2) monitoring can be used as an alternative to exhaust gas pCO2 (ExCO2) to calculate VCO2i. Methods PvCO2 and ExCO2 were monitored continuously during 40 elective coronary artery bypass grafting (CABG) procedures. VCO2i was calculated with ExCO2 as well as PvCO2. Results Mean PvCO2 was 0.27 mmHg higher than mean ExCO2 (p < .001). The 95% limits of agreement of PvCO2 and ExCO2 were [-2.99, 3.53] mmHg which is within the limits proposed by the Clinical Laboratory Improvement Amendments of 2019. VCO2i was calculated using both PvCO2 and ExCO2 (PvVCO2i; ExVCO2i). A strong linear correlation was found for ExVCO2i and PvVCO2i (R2= .94, p < .001). Conclusion In conclusion, the differences in VCO2i calculation between the two methods are unlikely to be clinically relevant during normothermic CABG procedures. VCO2i can be calculated with either a capnograph or inline venous pCO2 monitoring.