NEONATAL CEREBRAL ARTERIAL FLOW VELOCITY WAVE-FORMS IN TERM INFANTS WITH AND WITHOUT METABOLIC-ACIDOSIS AT DELIVERY

To define the effects of acid base status at delivery on neonatal cere bral artery flow velocity waveform patterns obtained using Doppler ult rasound during the first week of life, a longitudinal comparative stud y of neonates born at term with and without evidence of metabolic acid osis in the umbilical artery was undertaken. Eighty-two appropriate fo r gestational age infants delivered after uncomplicated pregnancies wi th non-acidotic umbilical artery blood gases and in whom no neonatal c omplications were noted were studied to establish reference values of neonatal cerebral arterial vascular resistance index (RI) in normal te rm infants during the first week of life. A further 189 infants were g rouped according to the presence and severity of metabolic acidosis at delivery, and also the presence of high risk features in the antenata l period. In the normal non-acidotic infants, over the first 24 h of l ife, there was a significant fall in the cerebral arterial resistance index (RI) in all the vessels examined, after which a steady state val ue was attained with no significant changes in vascular resistance ind ex being noted during the remainder of the study period. The fall in R I between 12 and 24 h of age was consistent in all study groups. Infan ts with metabolic acidosis at delivery had blood flow patterns compati ble with decreased resistance to flow in both anterior and middle cere bral arteries which persisted throughout the first week of life. This reduction in cerebral vascular resistance was most marked in those inf ants with severe metabolic acidosis. The majority of severely acidotic infants had a benign clinical outcome in the first week of life and a ll infants had normal cerebral ultrasound scans during the neonatal pe riod. These findings suggest that metabolic acidosis at birth is assoc iated with changes in neonatal cerebral arterial vascular resistance d uring the first week of life, and in the presence of a benign clinical course the significance of this observation with regard to neurodevel opmental outcome requires evaluation.