End-Tidal CO₂ for Prediction of Cardiac Output Following Weaning from Cardiopulmonary Bypass

¹ Professor and Chairman, Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon
² Associate Professor, Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon
³ Chief Resident, Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon
⁴ Professor, Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon

^* Address correspondence to: Anis Baraka, MD, FRCA, Professor and Chairman, Department of Anesthesiology, American University of Beirut Medical Center, P.O. Box 11 0236, Beirut, 1107 2020, Lebanon. E-mail: abaraka@aub.edu.lb

Abstract

This prospective study included 32 patients undergoing cardiopulmonary bypass (CPB) for elective coronary artery bypass grafting correlates the respiratory end-tidal CO₂ (ETCO₂) during partial separation from CPB with cardiac output (CO) following weaning from CPB. After induction of general anesthesia, a pulmonary artery catheter was inserted for measurement of cardiac output by thermodilution. Patients were monitored using a 5-lead ECG, pulse oximeter, invasive blood pressure monitoring, rectal temperature probe, and end-tidal capnography. At the end of surgery, patients were weaned from CPB in a stepwise fashion. Respiratory ETCO₂ and in-line venous oximetry were continuously monitored during weaning. The ETCO₂ was recorded at quarter pump flow and after complete weaning from CPB. Following weaning from CPB, CO was measured by thermodilution. The CO values were correlated with the ETCO₂ during partial bypass and following weaning from bypass. Regression analysis of ETCO₂ at quarter-flow and post-bypass CO showed significant correlation (r = 0.57, p < .001). Also, regression analysis of ETCO₂ after complete weaning from bypass and post-bypass CO showed significant correlation (r = 0.6, p = .002). The correlation between ETCO₂ and CO showed that an ETCO₂ >30 mm Hg during partial CPB will always predict an adequate CO following weaning from CPB. An ETCO₂ <30 mm Hg may denote either a low or a normal cardiac output and hence other predictive parameters such as SvO₂ must be added.