Monitoring end-tidal carbon dioxide during weaning from cardiopulmonary bypass in patients without significant lung disease.

End-tidal carbon dioxide tension (PETCO(2)) changes with fluctuations in cardiac output (CO). We compared PETCO(2) 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, PETCO(2) 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 PETCO(2). Regression and bias analyses were used to compare PETCO(2), 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 PETCO(2) (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 PETCO(2) showed greater variability at PETCO(2) levels > 34 mm Hg (n = 22; r = 0.14). Increases in PETCO(2) plateaued at this level, although PAQt continued to increase. When PETCO(2) was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m(2)). When PETCO(2) exceeded 34 mm Hg, all values of PAQt, and 28/29 values of TDCO were more than 5 L/min (>2.5 L/min/m(2)). One patient had TDCO of 4.69 L/min (2.39 L/min/m(2)). In normothermic patients without significant pulmonary disease, PETCO(2) is a useful index of PAQt during separation from CPB. Under the clinical settings in this study, a PETCO(2) 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/m(2).