Background and aims We describe resistive index (RI) values in various cerebral arteries in a cohort of preterm infants born at <29 weeks gestation. We also aim to compare RI in various intracranial arteries, and to assess the relationship between RI and hemodynamically significant patent ductus arteriosus (PDA).

Methods Preterm infants admitted to our NICU between May 2010 and January 2013 were enrolled. RI of internal carotid arteries, basilar artery, anterior cerebral artery, pial and striatal arteries was obtained in the first three days of life and weekly after that until discharge or death.

Results 771 examinations were performed in 235 infants. RI differed depending on which artery was insonated. RI was negatively correlated with measured time averaged velocity, except in the basilar artery. There was a significant difference in RI when comparing left (mean 0.86) to right sided (0.84) internal carotid artery (p = 0.023). RI was lower in patients without PDA compared to patients with hemodynamically significant PDA, though this difference was small and not statistically significant in all arteries. There was no difference in pre- and postligation RI in patients who underwent PDA ligation. RI was not related to gestational age, postnatal age, SNAPPE II score or gender.

Conclusions For accurate follow-up and comparison of RI, it is important to examine the same artery. No definitive cut-off value for RI indicative for the presence of a hemodynamically significant PDA was found. Cerebral artery RI may have limited value as a clinical tool in the very preterm infant.