Association between umbilical cord artery pCO₂ and the Apgar score; elevated levels of pCO₂ may be beneficial for neonatal vitality after moderate acidemia

The Risk of Neonatal Morbidity in Umbilical Artery Hypercarbia and Respiratory Acidosis

OBJECTIVE

 To test the hypothesis that elevated umbilical artery (UA) partial pressure of carbon dioxide (pCO2) is associated with neonatal morbidity and to compare the risk of neonatal morbidity with different patterns of UA acidosis.

STUDY DESIGN

 This was a secondary analysis of a prospective cohort of term, singleton, nonanomalous deliveries with universal cord gas collection. The primary outcome was composite neonatal morbidity. Multivariable logistic regression was used to determine the relative risk (RR) for neonatal morbidity in patients with and without UA hypercarbia. A receiver operating characteristic curve determined the predictive value of pCO2 for neonatal morbidity. An additional multivariable logistic regression was used to evaluate the risk of neonatal morbidity in different patterns of UA acidosis.

RESULTS

 UA hypercarbia was associated with an increased risk of neonatal morbidity (RR: 2.56, 95% confidence interval [CI]: [2.07, 3.17]). After adjusting for UA acidemia, this association remained significant (adjusted RR: 1.39, 95% CI: [1.05, 1.83]). UA pCO2 was less predictive of neonatal morbidity than UA pH (area under the curve [AUC]: 0.65, 95% CI: [0.62, 0.68] vs. AUC: 0.72, 95% CI: [0.69, 0.75], p < 0.01). The odds ratios for neonatal morbidity for respiratory, mixed, and metabolic acidosis compared with normal cord gases were 1.48 (95% CI: [0.88, 2.49]), 6.41 (95% CI: [3.68, 11.17]), and 7.49 (95% CI: [5.76, 9.72]), respectively, p-trend < 0.01.

CONCLUSION

 UA hypercarbia is an independent predictor of neonatal morbidity, even in the setting of concomitant UA acidemia. UA mixed and metabolic acidosis carry significantly greater risk of neonatal morbidity compared with respiratory acidosis.

KEY POINTS

· UA pCO2 is associated with neonatal morbidity.. · UA respiratory acidosis is the UA cord gas pattern least associated with neonatal morbidity.. · UA pH is a superior predictor of neonatal morbidity compared with UA pCO2..

Is it time to end the use of base deficit for fetal well-being assessment?

Authors have expressed reservations regarding the use of base deficit measured in umbilical artery blood samples to assess fetal well-being during the course of labor and to predict neonatal neurologic morbidity. Despite its integration into clinical practice for more than 50 years, obstetricians and maternal-fetal medicine specialists may not realize that this marker has significant limitations in accurately identifying neonatal metabolic acidosis as a proxy for fetal well-being. In brief, there are 2 large families of base deficit, namely whole blood and extracellular fluid. Both rely on equations that use normal adult acid-base characteristics (pH 7.40 and partial CO2 pressure of 40 mm Hg) that overlook the specificity of the normal in utero acid-base status of pH 7.27 and partial CO2 pressure of 54 mm Hg. In addition, it ignores the unique characteristic of the in utero fetal response to acute hypoxia. The dependence on placental circulation for CO2 elimination may lead to extremely high values (up to 130 to 150 mm Hg) during hypoxic events, a phenomenon that is absent in adults with acute metabolic acidosis who can hyperventilate. The dispute over if to include a correction for high partial CO2 pressure in the bicarbonate estimation, as presented in the Great Trans-Atlantic Debates, remains unresolved. The key constants computed for adult acid-base physiology in the current base deficit algorithms, without accounting for the impact of high partial CO2 pressure or other fetal characteristics of buffering capacity (eg, differences in body water content composition, plasma protein, and hemoglobin attributes), may lead to an overestimation of metabolic acidosis, especially in newborns who are experiencing hypercarbia during the early stages of the hypoxic response. These unrecognized limitations impact the base deficit results and may mislead clinicians on fetal well-being assessments when discussing the management of fetal heart rate monitoring and neonatal outcomes. Based on our arguments, we believe that it is prudent to consider an alternative to base deficit for drawing conclusions regarding fetal well-being during the course of birth management. We propose a marker specifically related to the newborn acid-base physiology--the neonatal eucapnic pH correction. This marker can be added to arterial cord blood gas analysis, and we have described how to interpret it as a marker of neonatal metabolic acidosis.

Umbilical cord blood acid-base analysis at birth and long-term neurodevelopmental outcomes in children: a systematic review and meta-analysis

BACKGROUND

Umbilical cord blood acid-base sampling is routinely performed at many hospitals. Recent studies have questioned this practice and the association of acidosis with cerebral palsy.

OBJECTIVE

To investigate the associations between the results of umbilical cord blood acid-base analysis at birth and long-term neurodevelopmental outcomes and mortality in children.

SEARCH STRATEGY

We searched six databases using the search strategy: umbilical cord AND outcomes.

SELECTION CRITERIA

Randomised controlled trials, cohorts and case-control studies from high-income countries that investigated the association between umbilical cord blood analysis and neurodevelopmental outcomes and mortality from 1 year after birth in children born at term.

DATA COLLECTION AND ANALYSIS

We critically assessed the included studies, extracted data and conducted meta-analyses comparing adverse outcomes between children with and without acidosis, and the mean proportions of adverse outcomes. The certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluations approach.

MAIN RESULTS

We have very low confidence in the following findings: acidosis was associated with higher cognitive development scores compared with non-acidosis (mean difference 5.18, 95% CI 0.84-9.52; n = two studies). Children with acidosis also showed a tendency towards higher risk of death (relative risk [RR] 5.72, 95% CI 0.90-36.27; n = four studies) and CP (RR 3.40, 95% CI 0.86-13.39; n = four studies), although this was not statistically significant. The proportion of children with CP was 2.39/1000 across the studies, assessed as high certainty evidence.

CONCLUSION

Due to low certainty of evidence, the associations between umbilical cord blood gas analysis at delivery and long-term neurodevelopmental outcomes in children remains unclear.

Review of the Reliability and Validity of the Apgar Score

BACKGROUND

The Apgar score is the most common score used to quantify neonatal status after birth. It is routinely used in clinical practice and research. However, since its introduction there have been significant changes in peripartum and neonatal management, our understanding of neonatal physiology, and changes in data analysis capabilities.

PURPOSE

To assess the Apgar score's reliability and validity in the context of today's clinical and research environments.

METHOD

PubMed was searched using the term "Apgar." Just over 22,000 titles were identified. Full-text articles were obtained if they addressed the Apgar score's use, reliability, and validity, or if the score was a primary outcome measure. This was followed by a hand search using the same criteria. The 505 identified articles build the basis for this discussion of the Apgar score's reliability and validity.

FINDINGS

Multiple positive and negative aspects of the Apgar score's reliability and validity were identified. Some facets needed to evaluate reliability and validity do not seem to have been addressed in the literature. Overall, the identified concerns can introduce bias into outcomes obtained via the use of the Apgar score in both clinical practice and research.

IMPLICATIONS FOR PRACTICE

The Apgar score is no longer used to determine neonatal management in the delivery room.

IMPLICATIONS FOR RESEARCH

The use of the Apgar score in research may introduce bias into outcomes. As discussed in the Video Abstract, researchers need to address and improve the score's weaknesses or consider developing a new tool better suited to today's research needs.

VIDEO ABSTRACT AVAILABLE AT

https://journals.lww.com/advancesinneonatalcare/Pages/videogallery.aspx?autoPlay=false&videoId=45.

Umbilical artery carbon dioxide decreases the risk for hypoxic-ischaemic encephalopathy

AIM

An accurate biomarker for metabolic acidosis at birth is needed. Our aims were to investigate the link between umbilical artery pCO₂ and the risk for hypoxic-ischaemic encephalopathy (HIE) and to compare false-negative screen results in newborn infants with HIE using three umbilical artery blood gas biomarkers.

METHODS

From a cohort of newborn infants ≥35 weeks born in Ottawa, Canada, between January 2007 and December 2016, we highlighted those with HIE or who died. We compared the umbilical artery pCO₂ for matched pH >mean versus matched pH ≤mean. We compared false-negative rates for three umbilical artery biomarkers-pH <7.0, base deficit ≥16 mmol/L and neonatal eucapnic pH ≤7.14.

RESULTS

This study included 51 286 newborn infants, 51% male and a mean gestational age of 38.9 ± 1.5 weeks. The rate for HIE or death with umbilical artery pCO₂ for matched pH >mean was 22%, compared to 78% for matched pH ≤mean. In 60 HIE or deaths, the false-negative rate for umbilical artery neonatal eucapnic pH ≤7.14 was 8%; compared to 31% for pH <7.00 and 36% for base deficit ≥16 mmol/L.

CONCLUSION

The rate of HIE or death is lower in newborn infants with higher pCO₂ . Using neonatal eucapnic pH decreases the risk of missing newborn infants with HIE.

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.

Umbilical artery base deficit/excess: sailing blindly in a thick fog

Assessing the wellbeing of newborns at birth with base deficit (BD)/base excess(BE) is well anchored in clinicians' practice. However, clinicians may not fully understand the concepts behind BD and the concerns regarding the validity of BD results provided by the hospital laboratory. These concerns are linked to the inconsistencies between the equations to calculate BD, and that these equations do not consider the aspects of acid-base physiology at birth. Additionally, the evidence-based supporting BD threshold in the literature to help physicians in making decisions is rather insufficient. These considerations support the need to review practice guidelines that use BD to guide decisions and bring to an end to clinicians to sail blindly in a thick fog.

Continuous End-Tidal Carbon Dioxide Monitoring during Resuscitation of Asphyxiated Term Lambs

BACKGROUND

The Neonatal Resuscitation Program (NRP) recommends close monitoring of oxygenation during the resuscitation of newborns using a pulse oximeter. However, there are no guidelines for monitoring carbon dioxide (CO2) to assess ventilation. Considering that cerebral blood flow (CBF) correlates directly with PaCO2, continuous capnography monitoring of end-tidal CO2 (ETCO2) may limit fluctuations in PaCO2 and, therefore, CBF during resuscitation of asphyxiated infants.

OBJECTIVE

To evaluate whether continuous monitoring of ETCO2 with capnography during resuscitation of asphyxiated term lambs with meconium aspiration will prevent fluctuations in PaCO2 and carotid arterial blood flow (CABF).

METHODS

Fifty-four asphyxiated term lambs with meconium aspiration syndrome were mechanically ventilated from birth to 60 min of age. Ventilatory parameters were adjusted based on clinical observation (chest excursion) and frequent arterial blood gas analysis in 24 lambs (control group) and 30 lambs (capnography group) received additional continuous ETCO2 monitoring. Left CABF was monitored. We aimed to maintain PaCO2 between 35 and 50 mm Hg and ETCO2 between 30 and 45 mm Hg.

RESULTS

There was a significant correlation between ETCO2 and PaCO2 (R = 0.7, p < 0.001), between PaCO2 and carotid flow (R = 0.52, p < 0.001) and between ETCO2 and carotid flow (R = 0.5, p < 0.001). PaCO2 and CABF during the first 60 min of age showed significantly higher fluctuation in the control group compared to the capnography group.

CONCLUSION

Continuous monitoring of ETCO2 using capnography with mechanical ventilation during and after resuscitation in asphyxiated term lambs with meconium aspiration limits fluctuations in PaCO2 and CABF and may potentially limit brain injury.

Improvements in fetal heart rate analysis by the removal of maternal-fetal heart rate ambiguities

Background

Misinterpretation of the maternal heart rate (MHR) as fetal may lead to significant errors in fetal heart rate (FHR) interpretation. In this study we hypothesized that the removal of these MHR-FHR ambiguities would improve FHR analysis during the final hour of labor.

Methods

Sixty-one MHR and FHR recordings were simultaneously acquired in the final hour of labor. Removal of MHR-FHR ambiguities was performed by subtracting MHR signals from their FHR counterparts when the absolute difference between the two was less or equal to 5 beats per minute. Major MHR-FHR ambiguities were defined when they exceeded 1 % of the tracing. Maternal, fetal and neonatal characteristics were evaluated in cases where major MHR-FHR ambiguities occurred and computer analysis of FHR recordings was compared, before and after removal of the ambiguities.

Results

Seventy-two percent of tracings (44/61) exhibited episodes of major MHR-FHR ambiguities, which were not significantly associated with any maternal, fetal or neonatal characteristics, but were associated with MHR accelerations, FHR signal loss and decelerations. Removal of MHR-FHR ambiguities resulted in a significant decrease in FHR decelerations, and improvement in FHR tracing classification.

Conclusions

FHR interpretation during the final hour of labor can be significantly improved by the removal of MHR-FHR ambiguities.