Cardiac Output Measurements with UDCO and ECHO under general anesthesia during normotension, hypotension and hypertension in adult alpacas

Abstract

Cardiac output (CO) is defined as the quantity of blood pumped into the aorta each minute by the heart. Measurement of CO is considered an important tool to determine oxygen deliver to the tissues. Currently, there are several technics available to measure CO, some being considered more invasive than others. The accepted gold standard for CO measurement is pulmonary thermodilution with the use of a pulmonary arterial catheter (Swan Ganz technic). Ultrasound dilution (UDCO) and transthoracic echocardiography (ECHO) are minimally invasive methods of CO measurement and were investigated in alpacas. Six alpacas (3 female, 3 male, 62.6 to 88.7 kgs) were anesthetized with propofol and maintained in right lateral recumbency with isoflurane and mechanically ventilated. An external arterial-venous loop with ultrasound probes for UDCO measurement was placed. A 30 ml saline bolus was injected into the venous end of the loop and CO was calculated as area under the curve from transient blood protein dilution. An ultrasound probe was placed against the right chest wall and CO was estimated by stroke volume (SV) measured via three different methods and multiplied by heart rate: ECHO M-mode left ventricular internal diameter (LVID), aortic valve flow (Ao Linear), and mitral valve flow (Min flow). Measurements were taken during normotension (NORM, MAP 60 to 80 mm Hg), hypotension induced with isoflurane (HYPO, MAP < 60 mm Hg) and hypertension induced with phenylephrine (HYPER, MAP > 80 mm Hg). Bland-Altman plots were used to compare UDCO with ECHO. Data are reported as median (range). A Friedman test with a post hoc Dunn´s test for multiple comparisons between groups when significant was used for analysis. A p value  0.05 was used for significant. The UDCO and ECHO M-mode had the best agreement (Bias: NORM -0.44, HYPO 1.04, and HYPER -1.14 L mim-1). Mean bias between UDCO and ECHO-Ao Linear or ECHO-min flow were considered clinically unacceptable. For UDCO, CO was 4.3 (3.03, 5.74), 4.46 (2.14, 4.63), and 6.62 (4.22, 8.9) L min-1 for NORM, HYPO and HYPER respectively. For CO measurement in alpacas, only ECHO M-mode appears to have an acceptable level of agreement with UDCO. UDCO may prove useful results for CO measurement in alpacas.