Quantification of left-to-right shunt through Patent Ductus Arteriosus by colour Doppler

Abstract: The aim of this thesis was to develop a non-invasive method to quantify the size of a shunt through a patent ductus arteriosus (PDA) by ultrasound and to test its usability in clinical settings. There is no consensus regarding the optimal management strategy for a PDA in premature infants. Non-steroidal anti-inflammatory drugs (NSAID) are the first treatment of choice. The use of NSAIDs, especially indomethacin, should be carefully balanced, as they have their disadvantages. In our experimental study in lambs, indomethacin acutely reduced the coronary flow by up to 50% and the effect lasted for up to one hour. In our lamb model, we developed a non-invasive method to quantify the ductal shunt by ultrasound. The flow was measured with electromagnetic flow meters in the ascending aorta and in the ductus and a colour Doppler image was obtained simultaneously over the main pulmonary artery longitudinal cross-section including ductal inflow. The percentage of colour pixels representing ductal flow was quantified in the main pulmonary artery outlined by anatomic landmarks. There was a correlation between the ratio of pulmonary to systemic flow (Qp/Qs) and the percentage of total colours covering the cross-section and there was an even better correlation with green pixels alone. When the Qp/Qs was ≥ 1.5:1, the percentage of green pixels in PALS was ≥ 50. In children admitted for the device closure of the open ductus, the method had 92% sensitivity for a measured Qp/Qs of ≥ 1.5. In preterm infants during the first three days of life, the ductal diameter but not the quantified ductal shunt predicted the need for treatment. We showed further that the perinatal cytokine burden during the first three days of life is not associated with an increased need to close the ductus, but it is associated with increased ductal diameter and reduced systolic blood pressure.
We suggest that our method could be used as a non-invasive tool to determine a haemodynamically significant ductal shunt. Using the evaluated Qp/Qs of > 1.5:1 as a guide for treatment decisions might reduce the need for unnecessary interventions and reduce complications.