[Neonatal eucapnic pH at birth: Application in a cohort of 5392 neonates]

To apply a newly concept of neonatal eucapnic pH at birth [pH euc (n)] and compare its contribution towards conventional criteria of severe metabolic acidosis.

Analysis of a cohort of 5392 neonates from 2010 to 2014 in a level 1 maternity. clinical data (birth weight, gestational age, mode of delivery, APGAR score) were collected from archived files. Biological data were collected from umbilical cord blood, consisting of pH, PCO2, Base deficit, lactate. Eucapnic pH and eucapnic base deficit were calculated from pH and PCO2 with the Henderson-Hasselbalch equation applied in the Charles-Racinet diagram and/or with an Excel spreadsheet.

Data set the prevalence of neonatal acidemia<7.00 to 0.62 %. The current cohort shows 32 cases of severe neonatal metabolic acidosis according to ACOG-AAP (2014) criteria and 26/29 cases according to McLennan (2015) criteria, of which 80 % were born by cesarean section or instrumental delivery. In 55 % of cases, calculated eucapnic pH at birth did not confirm the severity of metabolic acidosis based on a threshold set at 7.11. Five cases were transferred in neonatalogy only on clinical considerations of poor neonatal adaptation but not on biological consideration (pH euc<7.11 was equally distributed between transferred and non-transferred neonates, P=0.76; the same distribution was observed with the pH, P=0.20) and followed normal outcome.

The pH determination provides information only on the degree of acidemia and not on respiratory and/or metabolic components. Moreover, hypercapnia always present at birth is not included in the instructions to determine a metabolic acidosis (The American College of Obstetricians and Gynecologists, 2014; MacLennan et al., 2015). The new concept of neonatal eucapnic pH at birth accounts for only the metabolic component. We feel it should fine tune indications for cerebral hypothermia and thus improve its effectiveness. From a medicolegal perspective, for cases of cerebral palsy, it often allows to refute metabolic acidosis in perpartum events, often wrongfully being linked to generate cerebral injuries.