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 card iac output (CO). We compared PETCO2 to pulmonary artery blood flow (PAQt) d uring weaning from cardiopulmonary bypass (CPB) in normothermic patients wi thout significant pulmonary disease. Fifteen consecutive adult cardiac surg ical patients were prospectively studied during and shortly after weaning f rom CPB. Before separation from CPB, PETCO2 and PAQt were measured, the lat ter by transesophageal Doppler echocardiography. At the time of measurement s patients were normothermic, and ventilated at 6 breaths/min with tidal vo lumes of 10 mL/kg. After separation from CPB, thermodilution cardiac output (TDCO) was measured in addition to PAQt and PETCO2. Regression and bias an alyses were used to compare PETCO2, PAQt, and TDCO. Seventy measurements we re 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 betwee n TDCO and PAQt (r = 0.93; mean bias 0.03 L/min; SD 0.52 L/min). The regres sion 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 leve l, although PAQt continued to inc-ease. When PETCO2 was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m(2)). When PETCO2 ex ceeded 34 mm Hg, all values of PAQt,and 28/29 values of TDCO were more than 5 L/min (>25 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 PETCO2 greater than 30 mm Hg was invariably assoc iated with a CO more than 4.0 L/min or a cardiac index >2.0 L/min/m(2).