Oxygenator Exhaust Capnography for Prediction of Arterial Carbon Dioxide Tension During Hypothermic Cardiopulmonary Bypass

Continuous monitoring and control of arterial carbon dioxide tension (PaCO2) during cardiopulmonary bypass (CPB) is essential. A reliable, accurate, and inexpensive system is not currently available. This study was undertaken to assess whether the continuous monitoring of oxygenator exhaust carbon dioxide tension (PexCO2) can be used to reflect PaCO2during CPB. A total of 33 patients undergoing CPB for cardiac surgery were included in the study. During normothermia (37°C) and stable hypothermia (31°C), the values of PexCO2from the oxygenator exhaust outlet were monitored and compared simultaneously with the PaCO2values. Regression and agreement analysis were performed between PexCO2and temperature corrected-PaCO2and temperature uncorrected-PaCO2. At normothermia, a significant correlation was obtained between PexCO2and PaCO2(r = 0.79;p< 0.05); there was also a strong agreement between PexCO2and PaCO2with a gradient of 3.4 ± 1.9 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2and the temperature corrected-PaCO2(r = 0.78;p< 0.05); also, there was a strong agreement between PexCO2and temperature corrected-PaCO2with a gradient of 2.8 ± 2.0 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2and the temperature uncorrected-PaCO2(r = 0.61;p< 0.05); however, there was a poor agreement between PexCO2and the temperature uncorrected-PaCO2with a gradient of 13.2 ± 3.8 mmHg. Oxygenator exhaust capnography could be used as a mean for continuously monitoring PaCO2during normothermic phase of cardiopulmonary bypass as well as the temperature-corrected PaCO2during the stable hypothermic phase of CPB.