Influence of catecholamines at different dosages on the function of the LiDCO sensor in isoflurane anesthetized horses

Objective: To compare the lithium dilution method for cardiac output (LiDCO) and bolus-thermo-dilution (BTD) measurements before and during infusion of dobutamine, dopamine, phenylephrine, or noradrenaline at 2 different doses in anesthetized horses and to examine the correlation between sensor voltages (saline–blood exposed) and possible measurement errors. Design: Prospective experimental study. Setting: University teaching hospital. Animals: Nine Warmblood horses. Interventions: Following 90 minutes of equilibration, 3 different doses of dobutamine (0.5–3 μg/kg/min), dopamine (1–5 μg/kg/min), phenylephrine (0.5–3 μg/kg/min), or noradrenaline (0.1–0.5 μg/kg/min) were administered for 15 minutes in anesthetized horses, and measurements using the LiDCO were performed at the lowest and highest doses. Pairs of LiDCO and BTD measurements were collected and sensor voltages exposed to blood and saline were measured before and at the end of each infusion period. Agreement between LiDCO and BTD was assessed with the Bland–Altman method. Measurement and Main Results: The biases (2 standard deviations) before infusion of dobutamine, dopamine, phenylephrine, and noradrenaline were 1.1 (5.7), 1.6 (7.3), 0.2 (6.6), and 1.5 (4.1) L/min, respectively, and minimally and nonsignificantly changed following low-dose catecholamine infusions. Following infusion of higher doses, biases were significantly higher compared to baseline with 10.7 (7.8), 11.2 (11.9), 6.9 (11.7), and 3.5 (3.8) L/min, respectively. The difference between saline- and blood-exposed sensor voltage decreased during infusion of high doses of catecholamines with correlations (r_s = 0.62) between cardiac output differences and sensor voltage differences (saline-blood). Conclusions: This study demonstrated that catecholamines could lead to overestimation in a dose-dependent fashion in LiDCO measurements. Monitoring changes in sensor voltage differences (saline-blood) is a valuable and clinically applicable tool to predict errors in LiDCO measurements.