Presented at the Neonatal Society 2005 Autumn Meeting.
Groves AM1, Kuschel CA1, Knight DB1, Skinner JR2
1 Newborn Services, National Women’s Health, Auckland City Hospital, Auckland, New Zealand
2 Paediatric Cardiology, Starship Children’s Hospital, Auckland, New Zealand
Background: Patency of the ductus arteriosus is physiological in the first 48 hours of postnatal life in term and preterm infants. Although pulmonary and systemic pressures may remain relatively balanced at this time high volume ductal shunt (as assessed by reversal of diastolic descending aortic blood flow) has been seen as early as 7 hours postnatal age in some sick preterm infants (1).
Aims: To examine whether significant volume of ductal shunting is common in the first 48 hours, and to assess whether systemic perfusion as assessed by superior vena cava (SVC) blood flow is compromised by ductal shunting in the first 48 hours of postnatal life in preterm infants.
Methods: Infants <31 weeks gestation were examined by echocardiography at 5, 12, 24 and 48 hours postnatal age. Duct diameter and left ventricular output (LVO) were assessed by standard methods. SVC flow was assessed as described previously (2). Pattern of diastolic descending aortic (DAo) flow was assessed from a low subcostal sagittal view. The relationship between SVC flow and ductal size was examined using univariate regression analysis, with correction for potential confounding factors by multiple regression. Volumes of flow were compared between infants with and without diastolic DAo flow reversal using a Mann-Whitney test. The local regional ethics committee approved the study and informed parental consent was obtained in all cases.
Results: Eighty infants were studied, with median (range) birth weight 1060 (510-1900) grams and gestation 28 (24-30) weeks. Of infants with patent ducts, pure systemic to pulmonary shunting was seen in 66%, 85%, 89% and 95% of cases at 5, 12, 24 and 48 hours postnatal age respectively. At 5 hours ductal size was not associated with volume of SVC flow on univariate analysis. At 12 hours increased duct diameter was associated with decreased volume of SVC flow on univariate analysis (R2=0.095, p=0.006). This association remained significant when correcting for gestation, birth weight, antenatal steroid use and severity of respiratory disease on multivariate analysis (p=0.004), but not when correcting for pCO2 (p=0.24). Infants with duct diameter greater than the median and reversal of diastolic DAo flow had increased LVO (346 vs 268 ml/kg/min, p=0.0007), but not decreased SVC flow (p=0.76) when compared to infants with duct diameter greater than the median but no DAo reversal (Figure). Similar results were seen at 24 and 48 hours.
Conclusion: Even in early postnatal life ductal shunting is predominantly systemic to pulmonary. Increased volume of ductal shunt may not be independently associated with decreased upper body perfusion in the first 48 hours in preterm infants. In general, as volume of ductal shunt increases, left ventricular output increases, maintaining upper body perfusion.
Acknowledgements: Supported by the Starship Foundation and The Southern Trust
References
1. Evans N, Iyer P. Arch Dis Child Fetal Neonatal Ed 1995;72(3):F156-61.
2. Kluckow M, Evans N. Arch Dis Child Fetal Neonatal Ed 2000;82(3):F182-7