Our animal model suggests that quantification of ductal flow from colour Doppler pixels is possible. We aimed to clarify whether this method can be used to determine a clinically significant ductal shunt in children.

We retrospectively quantified ductal flow from saved images from 20 children who had been admitted for device occlusion of patent ductus arteriosus. Colour Doppler images over the main stem of the pulmonary artery were obtained in longitudinal cross-sections. The colour pixel percentages during diastole, representing ductal flow, were correlated with the documented shunt, measured invasively according to Fick's principle.

The ratio of pulmonary to systemic flow correlated best with the sum of the percentages of green colour pixels (r = 0.73, r2 = 0.54, p < 0.001). When the shunt was 1.5:1 or more, 12 out of 13 infants had 50% or more of the region of interest covered with green pixels – sensitivity 92%, specificity 71%. The correlation between ductal diameter and pulmonary-to-systemic flow ratio was less significant (r = 0.6, r2 = 0.37, p < 0.03).

We conclude that clinically significant shunts with pulmonary-to-systemic flow ratio over 1.5 can be diagnosed with this method where neither the size of the patient nor echocardiographic settings seem to be critical. The method could be used to provide an objective indication for ductal closure, but further prospective studies in children are needed to verify the power of the method.