The Level of Cardiac Output Affects the Relationship and Agreement Between Pulmonary Artery and Transpulmonary Aortic Thermodilution Measurements in an Animal Model

Objective: The authors investigated the relationship between pulmonary artery and transpulmonary aortic thermodilution cardiac output measurements under conditions of increasing cardiac output (CO). Design: Animal study with repeated simultaneous measurements comparing 2 cardiac output measurement techniques. Setting: Experimental animal facility of a university hospital. Participants: Ten female pigs. Interventions: In anesthetized pigs, an aortic thermistor catheter and a pulmonary artery catheter (PAC) were inserted. Then dobutamine was infused under continuous cardiac output (CCO) monitoring to target different levels of CO. After each L/min increase of CCO simultaneous aortic and PAC thermodilution, CO measurements were performed by using a bolus injection of cooled normal saline and the amount of thermal indicator loss (TL) was calculated. Measurements and Main Results: Pooled analysis of CO data with the method of Bland and Altman showed that aortic thermodilution CO was higher than PAC thermodilution CO with a bias of 3.8% ± 11.1%. The range of TL was 30.4% to −10.1%. Differential analysis according to the range of CO revealed that, in each animal under conditions of low CO, aortic thermodilution CO was higher than PAC thermodilution CO, whereas results were inverse under conditions of high CO. Conclusions: The authors concluded that the amount of CO differentially affects the relationship between aortic and PAC thermodilution CO. TL and recirculation may be the explanation for this finding.