Doppler and volumetric echocardiographic methods for cardiac output measurement in standing adult horses.

Abstract

BACKGROUND: Cardiac output (CO) is not routinely measured in critically ill adult horses because of invasiveness of currently validated methods. Noninvasive CO monitoring would complement clinical assessment of hemodynamic status in adult horses. HYPOTHESIS: Volumetric methods for measuring CO will have better agreement with lithium dilution than Doppler-based methods. ANIMALS: Eight healthy adult horses. METHODS: Prospective study. CO was manipulated with continuous rate infusions of dobutamine and romifidine to achieve high and low CO states, respectively. At each level, CO was measured by lithium dilution and various echocardiographic methods. Images stored as video loops were reviewed by an individual blinded to the lithium dilution results. RESULTS: Lithium dilution determinations of CO ranged between 16.6 and 63.0&#xa0;L/min. There was a significant effect of method of CO measurement (P&#xa0;<&#xa0;.001), but no significant effect of CO level (P&#xa0;=&#xa0;.089) or interaction between level and method (P&#xa0;=&#xa0;.607) on the absolute value of the bias. The absolute values of the bias of the right ventricular outflow tract (RVOT) Doppler, Simpson, 4-chamber area-length, and bullet methods [5.5, 6.1, 6.5, 8.8&#xa0;L/min, respectively] were significantly lower than that of the left ventricular outflow tract (LVOT) Doppler or cubic methods [14.8, 24.3&#xa0;L/min, respectively]. CONCLUSIONS AND CLINICAL IMPORTANCE: The 4-chamber area-length, Simpson, bullet, and RVOT Doppler provided better agreement with lithium dilution than the other methods evaluated. These methods warrant further investigation for use in critically ill adult horses.