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

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.

Eucapnic pH coupled with arterial cord pH improves hypoxic-ischemic encephalopathy prediction

OBJECTIVE

To consider the classical use of "pH < 7.0 and/or a base deficiency ≥12 mmol/L" as markers of the risk of neonatal hypoxic-ischemic encephalopathy (HIE), recalling various criticisms of the use of these markers in favor of that of neonatal eucapnic pH, which appears to be a better marker of this risk.

METHODS

Fifty-five cases of acidemia with pH < 7.00 were collected from a cohort from the Nice University Hospital with eight cases of HIE. We compared the receiver operating characteristics curves established from the positive likelihood ratio (+LR) for each case of: umbilical cord artery pH (pHa), neonatal eucapnic pH (pH euc-n) in isolation (not matched to pHa), and matched pHa to its own pH euc-n.

RESULTS

The areas under the curve (AUC) are identical for pHa and pH euc-n, but AUC for the matched pair pHa-pH euc-n appears superior but non-significant because of the small number in our cohort. However, using the bootstrap method, the partial AUC for a sensitivity greater than 75% indicates the significant superiority (P < 0.01) of the matched pair pHa-pH euc-n approach.

CONCLUSION

The originality of this study lies in the use of two methodologic approaches: (1) standardized partial analysis of the AUCs of the pHa curve and that of pHa matched to its own pH euc-n, and (2) bootstrap statistical technique, that allowed us to conclude (P < 0.01) that the combined use of pH measured at the cord coupled with its eucapnic correction is better for diagnosing metabolic acidosis and best predicting the risk of HIE.

Acid base and metabolic parameters of the umbilical cord blood and cerebral oxygenation immediately after birth

Objective

Aim was to investigate whether acid-base and metabolic parameters obtained from arterial umbilical cord blood affect cerebral oxygenation after birth in preterm neonates with respiratory support and in term neonates without respiratory support.

Study design

This was a post-hoc analysis of secondary outcome parameters of a prospective observational study including preterm neonates with and term neonates without respiratory support. Non-asphyxiated neonates with cerebral oxygenation measured with near-infrared spectroscopy during the first 15 min and with blood gas analyses from arterial umbilical cord blood were included. Arterial oxygen saturation (SpO2) and heart rate (HR) were monitored with pulse oximetry. Potential correlations were investigated between acid-base and metabolic parameters (pH-value, bicarbonate, base-excess, and lactate) and crSO2/cFTOE 5 min after birth.

Results

Seventy-seven neonates were included: 14 preterm neonates with respiratory support (mean gestational age [GA] 31.4 ± 4.1 weeks; mean birth weight [BW] 1,690 ± 640 g) and 63 term neonates without respiratory support (GA 38.7 ± 0.8 weeks; BW 3,258 ± 443 g). Mean crSO2 5 min after birth was 44.0% ± 24.2% in preterm and 62.2% ± 20.01% in term neonates. Mean cFTOE 5 min after birth was 0.46 ± 0.06 in preterm and 0.27 ± 0.19 in term neonates. In preterm neonates with respiratory support higher lactate was significantly associated with lower crSO2 and SpO2 and tended to be associated with higher cFTOE. In term neonates without respiratory support no significant correlations were found.

Conclusion

In non-asphyxiated preterm neonates with respiratory support, lactate levels were negatively associated with crSO2 and SpO2, whereas in term neonates without respiratory support no associations were observed.

Acute tocolysis for intrapartum nonreassuring fetal status: how often does it prevent cesarean delivery? A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

This study aimed to evaluate the effectiveness of intrapartum acute tocolysis for nonreassuring fetal heart rate tracing in decreasing the incidence of cesarean delivery. Secondary outcomes included modes of delivery other than cesarean delivery, successful acute tocolysis, time-to-delivery interval, and short-term perinatal outcomes.

DATA SOURCES

Searches were performed in MEDLINE/PubMed, Embase, Scopus, the Cochrane Central Register of Controlled Trials and Reviews, ClinicalTrials.gov, and the International Clinical Trials Registry Platform from the inception of each database until February 2022.

STUDY ELIGIBILITY CRITERIA

Selection criteria included randomized controlled trials of laboring patients with singleton gestations randomized to receive intrapartum acute tocolysis for nonreassuring fetal heart rate tracing, as defined by the original trial.

METHODS

All analyses were done using an intention-to-treat approach, evaluating women according to the treatment group to which they were randomly allocated in the original trials. A frequentist network-meta-analysis was performed.

RESULTS

Four randomized clinical trials were eligible, including 605 patients with nonreassuring fetal heart rate tracing and singleton gestations at gestational ages >32 weeks. The cesarean delivery rate was similar among patients managed with different types of acute tocolysis. Acute tocolysis, compared with emergency delivery, was associated with improved neonatal acid-base status (notably decreasing the prevalence of base deficit >12 mmol/L [beta-2 agonists odds ratio, 0.61; 95% confidence interval, 0.37-0.99] and the rate of neonatal intensive care unit admission [beta-2 agonists odds ratio, 0.42; 95% confidence interval, 0.22-0.78]) and with an increase in the time-to-delivery interval (beta-2 agonists mean difference, 17.62 minutes; 95% confidence interval, 15.66-19.58); there was no reduction of cesarean delivery rate, showing an increased rate with atosiban and beta-2 agonists.

CONCLUSION

The cesarean delivery rate was not reduced by acute tocolysis when used for nonreassuring fetal heart rate tracing during labor. Acute tocolysis is associated with improved short-term fetal outcomes and safely increases the time-to-delivery interval.

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.