Determination of Cardiac Output by Ultrasound Dilution Technique in Infants and Children: A Validation Study against Direct Fick Principle

Background: Cardiac output (CO) monitoring is essential to guide cardiovascular therapy. Ultrasound dilution technique (UDT), a novel indicator method, was recently introduced to determine CO. The purpose of our study was to validate UDT against the “gold standard” reference technique, direct Fick principle, in children with congenital heart disease.

Methods: A total of 26 children (median age: 6 years 2 months, median weight: 19.2 kg), some with residual lesions (e.g., obstruction to ventricular outflow), underwent heart catheterization. Children with shunts, single ventricular circulation, or significant valvular regurgitation were excluded. CO was determined by Fick principle using measurement of oxygen consumption and invasive oximetry. Three independent measurements of CO followed with UDT. For the complete study group and an infant-type subgroup (n= 14), data were compared using bias and limits of agreement calculated as per Bland-Altman approach and linear regression analysis.

Results: Mean CO (confidence interval [CI]) values were 3.76 ± 1.73 L/min (range: 1.38 – 6.97, CI: 3.95 ± 0.83) for direct Fick principle and 3.49 ± 1.72 L/min (range: 1.31 – 7.00, CI: 3.64 ± 0.80) for UDT. An excellent correlation (r= 0.96) was found between both methods (p < 0.0001). Bland-Altman analysis demonstrated a good clinical agreement with mean bias of 0.26 L/min, limits of agreement of – 0.66 and 1.19 L/min and percentage error of 25.9%. Comparable results were obtained for the infant-type subgroup.

Conclusions: CO measurements by UDT agree favorably with Fick-derived data. UDT represents a valid and applicable method for repetitive CO determinations in infants and children. Further studies are necessary to evaluate accuracy and limitations of UDT in patients with intra- or extracardiac shunts or severe regurgitation.