Cardiac output measured by lithium dilution, thermodilution, and transesophageal Doppler echocardiography in anesthetized horses

Objective-To assess the suitability of lithium dilution as a method for mea suring cardiac output in anesthetized horses, compared with thermodilution and transesophageal Doppler echocardiography. Animals-6 horses (3 Thoroughbreds, 3 crossbreeds). Procedure-Cardiac output was measured in 6 anesthetized horses as lithium d ilution cardiac output (LiDCO), thermodilution cardiac output (TDCO), and t ransesophageal Doppler echocardiographic cardiac output (DopplerCO). For th e LiDCO measurements, lithium chloride was administered IV, and cardiac out put was derived from the arterial lithium dilution curve. Sodium nitropruss ide, phenylephrine hydrochloride, and dobutamine hydrochloride were used to alter cardiac output. Experiments were divided into 4 periods. During each period, 3 LiDCO measurements, 3 DopplerCO measurements, and 3 sets of 3 TD CO measurements were obtained. Results-70 comparisons were made between LiDCO, DopplerCO, and triplicate T DCO measurements over a range of 10 to 43 L/min. The mean (+/- SD) of the d ifferences of LiDCO - TDCO was -0.86 +/- 2.80 L/min; UDCO = -1.90 + 1.05 TD CO (r = 0.94). The mean of the differences of DopplerCO - TDCO was 1.82 +/- 2.67 L/min; DopplerCO = 2.36 +/- 0.98 TDCO (r = 0.94). The mean of the dif ferences of LiDCO - DopplerCO was -2.68 +/- 3.01 Vmin; LiDCO = -2.53 + 0.99 DopplerCO (r = 0.93). Conclusions and Clinical Relevance- These results indicate that lithium dil ution is a suitable method for measuring cardiac output in horses. As well as being accurate, it avoids the need for pulmonary artery catheterization and is quick and safe to use. Monitoring cardiac output during anesthesia i n horses may help reduce the high anesthetic mortality in this species.