OBJECTIVE: To assess the agreement of transpulmonary thermodilution (TPTD) and transpulmonary ultrasound dilution (TPUD) against direct measurement of main pulmonary artery flow with an ultrasound transit time flow probe (UTF) over a wide range of conditions in anesthetized cats. Additionally, the trending ability of TPTD, TPUD, and esophageal Doppler ultrasonography (EDU) was evaluated against UTF. METHODS: 12 purpose-bred cats were used. One cat was used for a pilot study. The cats were instrumented according to the manufacturer's recommendation. Paired measurements were made over a wide range of cardiac output. Agreement was analyzed with Bland-Altman analysis with repeated measures, and trending ability was assessed by 4-quadrant plot and concordance rate. Interchangeable was defined as percentage error less than simplified total error. Acceptable trending was defined as concordance rate >
95%. RESULTS: Bias and percentage error were -0.084 L·min-1 and 38.2% for TPTD and -0.041 L·min-1 and 52.9% for TPUD. The concordance rate was 100%, 95.5%, and 64% to 65% for TPTD, TPUD, and EDU, respectively. CONCLUSIONS: Both TPTD and TPUD were not interchangeable to UTF. Both TPTD and TPUD provided acceptable trending ability but not EDU. CLINICAL RELEVANCE: Transpulmonary thermodilution and TPUD allow detection of the direction of cardiac output changes in anesthetized cats but not EDU. Clinical and research use of these 3 devices warrants careful consideration of the limitations presented in this study.