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Acidemia in neonates with a 5-minute Apgar score of 7 or greater – What are the outcomes?

American Journal of Obstetrics and Gynecology, In Press, Uncorrected Proof, Available online 31 May 2016, Available online 31 May 2016

Editor’s comment: Prof. Dan Farine: Acidemia with Normal pH

This interesting study looks retrospectively at the rare occurrence of acidemia and/or low base access in babies with normal Apgar scores. The “common sense approach” has been to assume that the test is erroneous as the baby was doing well and ignore it. In Medico-Legal conferences the rationale for pushing for universal cord pH testing has been that it may identify the group of interest for asphyxia (low pH and Apgar scores). According to this approach it was even more interesting to identify the neonates with a normal pH and base excess. These babies may have been exposed to a hostile intra-uterine environment based on history and/or abnormal fetal heart rates and possibly to less than optimal care. However, since they were not acidotic they would not go on to develop cerebral palsy based on the McLennan dogma that was adopted by the major obstetrical societies (FIGO, ACOG, UK guidelines Australian-NZ ones etc.) In these babies the pH was used as a steel barrier preventing medico-legal suites. The group with abnormal pH and good Apgar scores and clinical outcome was believed to be irrelevant as the good clinical outcomes made the possibility of litigation quite remote. It was often regarded as an artifact and not a really low pH. In that respect, it is important to mention that our initial thoughts were found to be incorrect. We believed that unless the cord blood is obtained for testing fast it would deteriorate and result in a false low pH. There are now many studies that show again and again that this is not correct, and that a sample obtained after the cord was left without any cooling still maintained the original pH.

This study is another step in showing that our concepts have been simplistic. A low pH or BE shows that there was anaerobic metabolism but is this equivalent to brain damage? The answer is obviously only sometimes. As adults if one is choked or drowns there is a chance for a full recovery is long as the insult is not prolonged and there was no chronic insult. It is even truer for babies who have brains with better abilities to recuperate. The pH that is really important is the intra-cellular one and not the blood one. There is some data imaging techniques can obtain data on tissue pH. However, this promising approach is not clinical yet. There are two buffering system that to some extent manage to reduce the acidosis. One is the albumin in the blood and the other is the erythrocytes. The pH measured in the fetal cord does not assess directly to what extent these system are used and more importantly – completely used.

So what do clinical studies show? These studies have shown again and again that the outcome could be quite different in babies with the same degree of acidosis. For example research emanating from Dutch data bases show that “only” 50% of babies that meet the criteria for intra-partum acidosis (ph<7.0) are damaged later in life while the other half have no residual damage. It also makes sense that the cut-off point of pH=7.00-7.05 is quite arbitrary. For example, the same Dutch group showed that there are some damaged babies with a cut-off level of 7.10. Interestingly, when this data was presented at the SMFM by a neonatologist his conclusion was “obstetrician should make sure that they do not deliver babies with pH lower than 7.10.

The paper outlines the obstetrical associations with the e combination of acidemia and good Apgars. Most of them (and especially the shoulder dystocia) may be associated with insults that were short in duration – which may explain the presentation.

All of the neonatal outcomes listed are short term (as expected from the design of the study). It may be extremely important to try to get the long term outcome of these babies to see if the old dogma of short term hypoxia and good long term outcome still holds. These kinds of studies are difficult to conduct in general but are likely to be even more difficult in view of concerns from the hospital and the obstetricians of opening a medico-legal Pandora box. However, such data will have immense impact on our knowledge.

Background

The Apgar score is universally used for fetal assessment at the time of birth, whereas, the collection of fetal cord blood gases is performed commonly in high-risk situations or in the setting of Apgar scores of <7, which is a less standardized approach. It has been well-established that neonatal acidemia at the time of delivery can result in significant neonatal morbidity and death. Because of this association, knowledge of the fetal acid-base status and detection of acidemia at the time of delivery can serve as a sensitive and useful component in the assessment of a neonate’s risk. Umbilical cord blood gas analysis is an accurate and validated tool for the assessment of neonatal acidemia at the time of delivery. Because the collection of fetal cord blood gases is not a standardized practice, it is possible that, with such a varied approach, some cases of neonatal acidemia are not detected, particularly in the setting of reassuring Apgar scores.

Objective

In a setting of universally obtained cord blood gases, we sought to identify the rates of acidemia and associated factors in neonates with 5-minute Apgar scores of ≥7.

Study Design

This retrospective cohort study identified all term, singleton, nonanomolous neonates with 5-minute Apgar scores of ≥7. The incidence of umbilical artery pH ≤7.0 or ≤7.1 and base excess ≤–12 mmol/L or ≤–10 mmol/L were examined overall and in association with obstetric complications and adverse neonatal outcomes. Chi-squared tests were used to compare proportions, and multivariable logistic regression was used to control for potential confounders.

Results

In this cohort, the incidence of an umbilical artery pH of ≤7.0 was 0.5%, of a pH ≤7.1 was 3.4%, of a base excess ≤–12 mmol/L was 1.4%, and of ≤–10 mmol/L was 4.0%. Rates of neonatal acidemia were greater in the setting of meconium (4.3% vs 3.2%; P<.001), placental abruption (13.2% vs 3.4%; P<.001), and cesarean deliveries (5.8% vs 2.8%; P<.001), despite normal 5-minute Apgar scores. Additionally, umbilical artery pH ≤7.0 was associated with an increased risk of respiratory distress syndrome (adjusted odds ratio, 6.5; 95% confidence interval, 2.9–14.3) and neonatal intensive care unit admission (adjusted odds ratio, 10.8; 95% confidence interval, 6.8–17.4). Base excess of ≤–12 mmol/L was also associated with an increased risk of neonatal sepsis (adjusted odds ratio, 4.7; 95% confidence interval, 1.9–12.1). Finally, when examined together, neonates with both a pH of ≤7.0 and base excess of ≤–12 mmol/L continued to demonstrate an increased risk of neonatal intensive care unit admission and respiratory distress syndrome, with adjusted odds ratios of 9.6 and 6.0, respectively. This risk persisted in neonates with a pH of ≤7.1 and base excess of ≤–10 mmol/L as well, with adjusted odds ratios of 4.5 and 1.1, respectively.

Conclusion

Because neonates with reassuring Apgar scores have a residual risk of neonatal acidemia that is associated with higher rates of adverse outcomes, the potential utility of obtaining universal cord blood gases should be further investigated.

Key words: acidemia, Apgar, neonatal outcome, umbilical cord blood gas.

Footnotes

Department of Obstetrics and Gynecology, Oregon Health and Science University, Portland, OR

Corresponding author: Bethany Sabol, MD.

The authors report no conflict of interest.

Cite this article as: Sabol BA, Caughey AB. Acidemia in neonates with a 5-minute Apgar score of 7 or greater – What are the outcomes?. Am J Obstet Gynecol 2016;•••:••••.