Interpretation
Overall EA use in vaginal birth in Austria was increasing over the last ten years, but still differ from other European countries with comparable health care systems.11,17,18The pH of umbilical arterial cord blood is a practical measure for evaluating foetal acidosis and is routinely measured with blood gas analysis.19Our findings were comparable to a single and a multicentre study, showing no relation of EA on neonatal morbidity, defined as pH<7.1, APGAR score after 5 minutes <7, neonatal resuscitation, or composite morbidity.20,21Anim-Somuah and colleagues could not demonstrate a significant difference in the frequency of acidosis, defined as pH<7.2 or 7.15 in a 2018 published Cochrane review comparing opioid administration or other non-epidural pain therapies and EA.3BE reflects metabolic acid-base abnormalities. The potentially beneficial effects of EA on BE may be explained by increased uterine blood flow after EA when hypotension is prevented, however observed effect estimates appear clinically not relevant. In a 2002 published meta-analysis of studies comparing EA with systemic analgesics, BE was less negative in the EA groups in randomised as well as observational studies.22
Even though AS5<7 was only present in 0.7% of neonates, it was significantly more often observed in the EA group (adjusted OR 1.18). A Swedish population-based study based on data from 1999-2008 demonstrated an adjusted OR of 1.27 for AS5<7 with EA, with quite similar rates (0.8% vs. 1.3%),11while in more recent trials, AS5<7 was not related to EA use.3,20When low concentrations of local anesthetics for EA were used in nulliparous women, AS5<7 was observed with an incidence of 0.15% and showed no significant difference to non-epidural opioid pain relief in a meta-analysis published by Liu et al. in 2004.23Short-term morbidity may be higher when prolonged duration of birth was present and instrumental delivery was applied, which could be the case when higher doses of local anesthetics potentially led to motor blockade. Both of these circumstances were present in the examined EA group without clear association to EA itself. This assumption is supported by a recently published survey, asking for current obstetric anaesthesia practice in Austria, in which 51% reported to use ropivacaine 0.2%, while only up to 11% using potent epidural opioid adjuncts to reduce local anaesthetic dose. Further, the survey revealed, that only 42% of respondents generally perform EA independently of cervical dilatation, making it more likely that the indication for EA was an already prolonged or unusually painful birth period.14 So, EA may be used more extensively in already complicated and complex or induced deliveries, in request for relief of emerging pain. This in mind, our data analysis was not adjusted for cases of EA, in which parturients received EA in a very late phase of delivery, probably not affecting birth progression at all, or were even given due to complications in progress of labour.
The association of admission to NICU with EA, even after correcting for instrumental delivery, duration of birth and episiotomy, may support an actual effect of EA as the underlining cause of admission. These findings may be in part explained by higher rates of neonatal encephalopathy11 or seizures10 and possible sepsis in mother and newborn with EA when maternal fever occurred, or with respiratory depression, e.g. due to opioid adjuncts.24 Unfortunately, NICU admission diagnoses are not documented in the registry, which makes it difficult to elucidate reasons and rationale explanations of the role of EA, especially with lack of information on the drugs applied. There was no association between overall perinatal mortality and EA in our collective, and an impact on mortality could generally be assumed to be more likely by secondary complications instead of EA itself. Hasegawa et al. stated that morbidity as assessed by pH and APGAR scores were associated with instrumental delivery, regardless of EA being used or not.25
The rate of instrumental delivery with vacuum or forceps was more than twofold increased in deliveries with EA (13.5% vs. 29.8%). Higher proportions of women experienced instrumental delivery with EA in a recent Cochrane review, although when studies conducted before 2005 were excluded, no difference was present anymore.3The authors direct this finding to modern techniques, e.g. low concentration of local anesthetics, intermittent bolus application and patient controlled analgesia. In a 2013 published meta-analyses comparing low with higher concentration of local anesthetics for EA, the use of low concentrations, i.e. ropivacaine ≤0.17% or bupivacaine ≤0.1%, was also associated with a reduction in assisted vaginal delivery. When low concentration EA was compared with nonepidural analgesia, Wang et al. could not demonstrate any difference in instrumental delivery rates or prolonged second stage of labour in a 2017 published meta-analysis.26Importantly, the authors stated that also low-quality studies were included, with an overall decline in quality and certainty of the conclusions drawn. If EA was directly related to the tremendously higher rate of instrumental delivery in our study population, it may be due to divergence of practice from universally accepted guidelines in modern obstetric anesthesia.14Also, obstetricians may attempt an instrumental vaginal delivery more liberally with successful EA in place, leading to an increased number of difficult deliveries in the EA group. Wassen et al. showed that with increasing EA rates from 7.7% to 22% over ten years in the Netherlands, no similar increase in instrumental delivery was accompanied,27questioning the role of EA as a risk factor. Instrumental delivery is a known risk factor for higher grade perineal lacerations,28,29 although the differences between groups in our study were quite close (2.8 vs. 3.2%) and are comparable to the literature30–32 even with a more than twofold higher instrumental delivery rate with EA. The effect of EA on perineal lacerations is controversially reported, depending on the collective with beneficial,28,31,33 negative34or no impact.3 In women with vaginal birth receiving low dose combined spinal-epidural analgesia for vaginal birth, no association with neuraxial analgesia could be shown.35
The duration of labour was also markedly prolonged in the EA group. These findings differ from recent literature, describing an acceptable prolongation of the second stage of labour23,36or even no effect with low concentrations.26Still, the data of the National Registry gives no information on distinct stages and the timepoint of EA, hindering meaningful comparisons. The low EA rates let assume, that the choice of epidural use is more likely due to underlying circumstances of labour progress than the women’s choice, making it more likely that EA was used in already prolonged labour cases.

Conclusion

The results of this population-based registry study showed, that EA is only administered in 20% of nulliparous women undergoing a singleton vaginal delivery. For the primary outcomes pH and BE in umbilical cord blood, no worse short-term outcomes for neonates were associated with use of EA. The association of EA with increased NICU admission rates and Apgar scores below 7 after 5 minutes are most likely related to different indications for the use of neuraxial analgesia. Further insight into a causal relation between EA and neonatal outcome can only be gained when EA is applied independently of cervical dilatation, labour progress and underlying circumstances that led to these comparably low EA rates. A discussion on EA might enhance visibility and thereby improve the quality of care in obstetric anesthesia in Austria.

Disclosure of interests

The authors have no conflict of interest to declare.

Contribution to authorship

FK was involved in drafting and reviewing the manuscript, as well as gathering, analysing and interpreting the data. PW contributed in data analysis, writing and reviewing the final manuscript. ELM performed the statistical analysis and gave advice and input on data interpretation including review of the manuscript. HH helped design and direct the study, as well as manuscript revision. HL provided the data and was involved in drafting and revision of the manuscript. HK designed the study and organised the initiation and collaboration of all participating authors. He gave advice on data interpretation and was involved in drafting the manuscript. SJ gave valuable input in data interpretation and reviewed the draft and final manuscript. CMO helped with concept and writing of the manuscript, and gave advice on data interpretation. KUK was responsible for the design of the protocol, data interpretation, manuscript revision, and coordination of the research team.

Details of ethics approval

All analyses and gathering of data were initiated after approval (EK Nr: 1576/2018) by the ethics committee of the Medical University of Vienna, Austria (Chairperson Dr. Juergen Zezula) on 8 August 2018.

Funding

No funding, financial support or sponsorship was received.

Acknowledgements

Assistance with the study: none
Presentation: preliminary data for this study were presented as a poster presentation at the Euroanaesthesia meeting, 1-3 June 2019, Vienna.

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Table 1: Demographic and delivery characteristics