50 The Role of pCO2 in Umbilical Artery Gas Analysis: Predictive of Neonatal Morbidity?


      The purpose of this study was to estimate the relationship between umbilical artery (UA) partial pressure of carbon dioxide (pCO2) at time of delivery and neonatal morbidity at term. If a strong relationship could be established, reflecting impaired fetal gas exchange, this would serve to more effectively and accurately predict neonatal morbidity shortly after delivery and inform resource allocation.

      Study Design

      This was a secondary analysis of a prospective cohort study of term, singleton, non-anomalous deliveries with universal cord gas collection from 2010 to 2014. Patients were included if they had paired and validated umbilical cord gases. The primary outcome was composite neonatal morbidity including neonatal death, hypoxic-ischemic encephalopathy, suspected sepsis, seizures, hypotension requiring vasopressors and hypothermia treatment. Hypercarbia was defined as UA pCO2 75th percentile. Multivariable logistic regression and the Zhang method were used to determine adjusted relative risk for neonatal morbidity in patients with and without hypercarbia and accounting for acidemia (UA pH<7.2). A receiver operating characteristic (ROC) curve was created to determine the predictive value of pCO2 for neonatal morbidity.


      Of 8580 patients in the cohort, 7608 had validated cord gas data. 697 (9.2%) had composite neonatal morbidity. Hypercarbia was associated with an increased risk of neonatal morbidity (RR 1.58 [95% CI 1.37-1.83]). However, after adjusting for acidemia, this relationship was no longer significant (aRR 1.04 [95% CI 0.86, 1.25]). UA pCO2 was less predictive of neonatal morbidity than UA pH (AUC of 0.57 [0.55,0.59] vs 0.64 [0.62,0.66], p<0.01).


      Hypercarbia, reflecting impaired fetal gas exchange, is associated with increased neonatal morbidity but is likely due to the presence of concomitant acidemia. UA pCO2 alone is a poor predictor of neonatal morbidity.
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