Scientific Article

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

Address correspondence to: Anis Baraka, MD, FRCA, Chairman and Professor, Department of Anesthesiology, American University of Beirut, P.O. Box: 11-0236, Beirut, Lebanon, E-mail: abaraka@aub.edu.lb

Abstract

Continuous monitoring and control of arterial carbon dioxide tension (P_aCO₂) 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 P_aCO₂ during 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 PexCO₂ from the oxygenator exhaust outlet were monitored and compared simultaneously with the P_aCO₂ values. Regression and agreement analysis were performed between PexCO₂ and temperature corrected-P_aCO₂ and temperature uncorrected-P_aCO₂. At normothermia, a significant correlation was obtained between PexCO₂ and P_aCO₂ (r = 0.79; p < 0.05); there was also a strong agreement between PexCO₂ and P_aCO₂ with a gradient of 3.4 ± 1.9 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO₂ and the temperature corrected-P_aCO₂ (r = 0.78; p < 0.05); also, there was a strong agreement between PexCO₂ and temperature corrected-P_aCO₂ with a gradient of 2.8 ± 2.0 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO₂ and the temperature uncorrected-P_aCO₂ (r = 0.61; p < 0.05); however, there was a poor agreement between PexCO₂ and the temperature uncorrected-P_aCO₂ with a gradient of 13.2 ± 3.8 mmHg. Oxygenator exhaust capnography could be used as a mean for continuously monitoring P_aCO₂ during normothermic phase of cardiopulmonary bypass as well as the temperature-corrected P_aCO₂ during the stable hypothermic phase of CPB.