AIMSTo examine the hypothesis that right to left shunting occurs mainly in the lungs rather than through the fetal channels in neonates.
METHODSThirty two term babies requiring over 70% oxygen had daily colour Doppler echocardiograms until recovery. Measurements included left ventricular fractional shortening, right and left ventricular outputs, colour and pulsed Doppler ductal and atrial shunting and systolic pulmonary artery pressure (SPAP) derived from ductal shunt or tricuspid incompetence velocities.
RESULTSThe babies were retrospectively classified into a respiratory group (n=19) and a persistent pulmonary hypertension (PPHN) group (n=13) on the basis of clinical history and radiology. At the initial echocardiogram, just 50% of babies had suprasystemic SPAP. Despite better oxygenation, more of the PPHN group had suprasystemic PAP (85% vs 26%). A correlation between SPAP and Oxygen index (OI) was present only in the respiratory group (r=0.7). Low ventricular outputs (<150 ml/kg/min) were common in both groups (53% and 79%). The respiratory group had more closed ducts (47% vs 0%) and those ducts which were patent were more constricted (1.75mm vs 2.6 mm). Pure right to left ductal shunts were seen in just 15% and pure right to left atrial shunts in just 6% of all babies. The serial echocardiograms showed that SPAP fell and ducts closed well before oxygenation improved. Ventricular outputs increased with age in both groups.
CONCLUSIONSApart from early on in the sickest babies with a primarily respiratory diagnosis and the babies with primary PPHN, most right to left shunting occurred at an intrapulmonary level.

Keywords: pulmonary hypertension; echocardiography; right to left shunt