Neonatal cord blood eucapnic pH: A potential biomarker predicting the need for transfer to the NICU.

Introduction: The best biomarker for neonatal metabolic acidosis (NMA) and its related complications is still a matter of debate. Umbilical artery (Ua) cord pH is not sufficiently specific, as is lactatemia, while base deficit is considered to offer no added value. From a physiological point of view, the calculated neonatal eucapnic pH is a more specific marker for neonatal metabolic acidosis and may be a better predictor of birth complications of hypoxic origin, because complications related to asphyxia are always preceded by neonatal depression leading to a transfer to a neonatal intensive care unit (NICU) for close monitoring.

Objective: This study aimed to test the hypothesis that in a group of neonates with significant acidemia, neonatal eucapnic pH (pH euc-n) predicts NICU admission better than the Ua cord pH does.

Methods: From a cohort of 5,392 infants all born at ≥35 weeks' gestation, we identified a group of 30 cases with Ua cord pH <7.0. We calculated the area under the curve (AUC) for pH euc-n and Ua cord pH using the receiver-operating characteristic (ROC) curve and compared the performance of these biological markers in predicting transfer to the NICU. Cut-off points were determined by selecting the best value of the positive likelihood ratio that maximizes the accuracy of prediction.

Results: From the 30 newborns diagnosed with significant acidemia, four infants were transferred to the NICU. No case of neonatal encephalopathy was observed. In these infants, the pH euc-n AUC (0.66) was significantly higher than the Ua cord pH AUC (0.44) (P<0.005), with the best pH euc-n cut-off value at 7.11.

Conclusion: Despite the study limitations, our results suggest that pH euc-n is a better marker than Ua pH for predicting admission to the NICU in newborns with acidemia at birth. These are preliminary results and further investigations are mandatory in larger population samples to confirm these findings and to determine the optimal cut-off value for pH euc-n for the most accurate prediction of a complicated transition to extrauterine life and, potentially, neonatal hypoxic-ischemic encephalopathy.