Pediatric cardiac output measurement using surface integration of velocity vectors:: An in vivo validation study

Objective: To test Be accuracy and reproducibility of systemic cardiac output (CO) measurements using surface integration of velocity vectors (SIVV) in a pediatric animal model with hemodynamic instability and to compare SIVV with traditional pulsed-wave Doppler measurements. Design:Prospective, comparative study. Setting: Animal research laboratory at a university medical center. Subjects:Eight piglets weighing 10-15 kg. Interventions: Hemodynamic instability was induced by using inhalation of isoflurane and infusions of colloid and dobutamine. Measurements: SIVV CO was measured at the left ventricular outflow tract, the aortic valve, and ascending aorta. Transit time CO was used as the reference standard. Results:There was good agreement between SIVV and transit time CO. At high frame rates, the mean difference +/- 2 so between the two methods was 0.01 +/- 0.27 L/min for measurements at the left ventricular outflow tract, 0.08 +/- 0.26 L/min for the ascending aorta, and 0.06 +/- 0.25 L/min for the aortic valve. At low frame rates, measurements were 0.06 +/- 0.25, 0.19 +/- 0.32, and 0.14 +/- 0.30 L/min for the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. There were no differences between the three sites at high frame rates. Agreement between pulsed-wave Doppler and transit time CO was poorer, with a mean difference +/- 2 so of 0.09 +/- 0.93 L/min. Repeated SIVV measurements taken at a period of relative hemodynamic stability differed by a mean difference +/-2 so of 0.01 +/- 0.22 L/min, with a coefficient of variation = 7.6%. Intraobserver coefficients of variation were 5.7%, 4.9%, and 4.1% at the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. Interobserver variability was also small, with a coefficient of variation = 8.5%. Conclusions: SIVV is an accurate and reproducible flow measurement technique. It is a considerable improvement over currently used methods and is applicable to pediatric critical care.