Comparison of clinical performance of fick partial rebreathing CO₂ CO and transesophageal dual echo-Doppler CO in monitoring

Objective:To compare the performance of partial rebreathing CO₂ CO in monitoring and transesophageal dual echo-Doppler CO.Methods:Nine patients undergoing elective abdominal surgery were studied. Following anesthetic induction, CO was measured using partial rebreathing CO₂ monitor （NICO₂®） and transesophageal dual echo-Doppler（Hemosonic TM100） synchronously. Data were simultaneously recorded every 3min. NICO₂® continuously measures airway flow,pressure and CO₂ concentration. Pulmonary blood flow is estimated by tracking the CO₂ concentration and CO₂ elimination. CO is calculated from pulmonary blood flow by correcting for shunt.The sensor of transesophageal dual echo-Doppler was placed into the esophagus at the level of T3-4 interrib after tracheal intubation. The sensor faced backward toward descending aorta. Hemosonic TM100 can measure aorta blood flow（ABF）and ABF is closedly related to CO（CO=ABF/70%）. Linear regression and Bland-altman statistics were used to compare the degree of agreement between concurrent measurements of rebreathing CO and transesophageal CO. Results:The overall difference between rebreathing CO and transesophageal CO was -0.27±0.46L/min（bias±1SD）.The weighted correlation coefficient between rebreathing CO and transesophageal CO was r=0.76 （P＜0.01, n=278）.The regression equation was Rebreathing CO =0.76(Transesophageal CO +0.95. Conclusion:There was a significant correlation between CO values obtained with NICO₂® and Hemosonic TM100.Our data show that partial rebreathing CO₂ technique offers a good alternative to invasive and micro-invasive CO measurement.