Accuracy of Teichholz and Modified Simpson Echocardiographic Techniques for Measuring Cardiac Output in Northeastern Donkeys (Equus asinus).

Thermodilution is the reference method for cardiac output (CO) assessment but is invasive, limiting its routine use in equids. This study evaluated the Teichholz and Modified Simpson echocardiographic methods for CO estimation in five healthy Northeastern Brazilian donkeys (Equus asinus) during four evaluation sessions. Agreement with thermodilution was assessed using Spearman's correlation, Bland-Altman analysis, and linear mixed-effects models. Mean CO values obtained by thermodilution, Modified Simpson, and Teichholz were 9.94 ± 2.08, 7.75 ± 2.57, and 3.34 ± 1.16 L/min, respectively. The Modified Simpson method showed the strongest association and closest agreement with thermodilution among the echocardiographic methods evaluated, whereas Teichholz consistently underestimated CO. Although the Modified Simpson method cannot be considered interchangeable with thermodilution, these findings support its potential use as a non-invasive approach for CO estimation in donkeys.