FACTORS DETERMINING REOPENING OF THE DUCTUS-ARTERIOSUS AFTER SUCCESSFUL CLINICAL CLOSURE WITH INDOMETHACIN

Objective: To examine the role of ductus arteriosus (DA) constriction and loss of luminal blood flow in producing permanent closure of the DA in human infants. Methods: We studied 77 newborn infants (gestational age, 23 to 33 weeks) with asymptomatic patent ductus arteriosus (PDA), who had ''complete clinical closure'' (defined as the disappearance of all PDA signs) after treatment with indomethacin (three doses within 36 hours), All infants had an echocardiogram 24 to 36 hours after the last dose of indomethacin, They were then followed for the development of ductus reopening. Results: Despite the absence of clinical signs, 18 (23%) of 77 infants still had some residual luminal blood flow according to their echocardiograms. The failure to obliterate luminal blood flow completely was directly related to the infant's postnatal age when treatment was begun and to the amount of fluid administered before treatment. Subsequently the DA reopened in 16 (21%) of 77 infants. As predicted, infants with residual luminal blood flow after indomethacin treatment had a higher rate of subsequent clinical reopening than did those with no luminal flow, In addition, immature infants had a significantly higher reopening rate than did more mature infants. The increased risk of reopening in immature infants was seen even when indomethacin caused complete obliteration of ductus luminal blood flow. Conclusion: The DA of immature infants is resistant to the constriction-induced ischemic damage that is necessary for subsequent permanent closure of the vessel.