Performance of noninvasive partial CO₂ rebreathing cardiac output and continuous thermodilution cardiac output in patients undergoing aortic reconstruction surgery

Background: In the partial CO₂ rebreathing method, monitored changes in CO₂ elimination and end-tidal CO₂ in response to a brief rebreathing period are used to estimate cardiac output. However, dynamic changes in CO₂ production during ischemia and reperfusion may affect the accuracy of these estimates. This study was designed to compare measurements of cardiac output as produced by the partial CO₂ rebreathing (NICO), bolus (BCO), and continuous thermodilution (CCO) methods of monitoring cardiac output. Methods: Cardiac output was continuously monitored using both NICO and CCO in 28 patients undergoing aortic reconstruction. BCO measurements were taken at the following intervals when hemodynamic stability was achieved: (1) after anesthetic induction; (2) during aortic cross-clamp; (3) at reperfusion of the iliac artery; and, (4) during peritoneal closure. Results: The bias and precision (1 SD) derived from all the measurements between NICO and BCO was -0.58 ± 0.9 1/min, whereas for CCO and BCO it was 0.38 ± 1.17 1/min. The bias between NICO and BCO was small after anesthetic induction and during cross-clamp, but increased following reperfusion. The bias between CCO and BCO was relatively small until reperfusion but increased significantly at peritoneal closure. Conclusions: Results indicate that in aortic reconstruction surgery the performance of NICO monitoring is comparable with that of CCO; however, the direction of bias in these continuous measurement devices is the opposite.