Monitoring End-Tidal Carbon Dioxide During Weaning from Cardiopulmonary Bypass in Patients Without Significant Lung Disease

End-tidal carbon dioxide tension (Petco2) changes with fluctuations in cardiac output (CO). We compared Petco2 to pulmonary artery blood flow (PAQt) during weaning from cardiopulmonary bypass (CPB) in normothermic patients without significant pulmonary disease. Fifteen consecutive adult cardiac surgical patients were prospectively studied during and shortly after weaning from CPB. Before separation from CPB, Petco2 and PAQt were measured, the latter by transesophageal Doppler echocardiography. At the time of measurements patients were normothermic, and ventilated at 6 breaths/min with tidal volumes of 10 mL/kg. After separation from CPB, thermodilution cardiac output (TDCO) was measured in addition to PAQt and Petco2. Regression and bias analyses were used to compare Petco2, PAQt, and TDCO. Seventy measurements were recorded; 31 before separation from CPB and 39 after separation from CPB. A good correlation was seen between PAQt and Petco2 (r = 0.88) and between TDCO and PAQt (r = 0.93; mean bias 0.03 L/min; sd 0.52 L/min). The regression analysis of PAQt on Petco2 showed greater variability at Petco2 levels > 34 mm Hg (n = 22; r = 0.14). Increases in Petco2 plateaued at this level, although PAQt continued to increase. When Petco2 was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m2). When Petco2 exceeded 34 mm Hg, all values of PAQt, and 28/29 values of TDCO were more than 5 L/min (>2.5 L/min/m2). One patient had TDCO of 4.69 L/min (2.39 L/min/m2). In normothermic patients without significant pulmonary disease, Petco2 is a useful index of PAQt during separation from CPB. Under the clinical settings in this study, a Petco2 greater than 30 mm Hg was invariably associated with a CO more than 4.0 L/min or a cardiac index >2.0 L/min/m2. Implications In normothermic patients without pulmonary disease, acute changes in Petco2 during separation from cardiopulmonary bypass were reflective of changes in pulmonary artery blood flow. Specific Petco2 values were predictive of cardiac output values under the clinical conditions of the study.