A Combined Doppler Echocardiographic Investigation in Premature Infants with and without Respiratory Distress Syndrome

Abstract

Premature infants often develop the Respiratory Distress Syndrome (RDS). In the traditional view, this is due to a lack of surfactant causing a collapse of lung alveoli. In a number of cases of RDS, a Patent Ductus Arteriosus (PDA) with Left to Right (L-R) shunt is diagnosed during the recovery phase of the syndrome from the presence of a murmur, bounding pulses and an increased Left Atrium/Aorta ratio (LA/Ao). This diagnosis of the PDA has wrongly led to the conclusion that this L-R shunt first arises in the recovery phase; perhaps because routine clinical examination is not always sufficient to detect a PDA, since a large PDA with L-R shunt is not always acompanied by a heart murmur and even the echocardiographic demonstration of an increase in LA dimension or LA/Ao ratio is not conclusive evidence for the existence of a PDA with L-R shunt. Theoretically, a PDA with L-R shunt can cause respiratory problems, especially in small infants, as a result of pulmonary vessel engorgement, leading in turn to surfactant deficiency due to anoxaemia. So we have the situation indicated below:

SURFACTANT DEFICIENCY↔RDS↔PDA

In our investigation we demonstrated the existence of a PDA with L-R shunt in premature infants by means of a combined Doppler echocardiographic (DE) technique. The moment of closure of the ducus could be estimated from successive measurements. We also measured the LA/Ao ratio by means of echocardiography to determine the magnitude of the L-R shunt.

This research was sponsored by the Dutch Heart Foundation.