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

OBJECTIVE

To test the 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 SD 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 SD of 0.09+/-0.93 L/min. Repeated SIVV measurements taken at a period of relative hemodynamic stability differed by a mean difference +/-2 SD 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.