Comparison of standard and ultra-low local anaesthetic concentration for labour epidural analgesia: A critical review.

Abstract

Abstract: Epidural analgesia is the gold standard for labour pain management. Over the past two decades, there has been a shift towards using lower local anaesthetic concentrations to minimise motor blockade and associated obstetric complications[1]. This review critically examines the safety profile and analgesic efficacy of ultra-low concentration (ULC) versus standard concentration (SC) regimens in labour epidural analgesia, focusing on maternal, obstetric, and neonatal outcomes.

Methods: A systematic search of OVID MEDLINE, OVID EMBASE, COCHRANE, CINAHL, and ClinicalTrials.gov databases was conducted (January 2010 to September 2024) to identify randomized controlled trials comparing ULC (<0.1% bupivacaine/levobupivacaine or <0.2% ropivacaine) with SC (≥0.1% bupivacaine/levobupivacaine or ≥0.2% ropivacaine) regimens for labour epidural maintenance. Keywords and MeSH terms included labour, obstetric analgesia, epidural analgesia, and local anaesthesia. All epidural infusion regimens were included. Findings are reported as a narrative synthesis.

Results: Nine studies (n = 30–450) were included (Bupivacaine n = 4, Levobupivacaine n = 3, Ropivacaine n = 2). Seven used adjuvant opioids. Significant heterogeneity was observed in study designs, methods of administration (PCEA, PIEB, CEI, or combined), and outcome reporting. Three studies had low bias risk while four had high risk as assessed by the Cochrane Risk of Bias tool 2.0. All studies were included in the narrative review.

ULC regimens provided effective analgesia, particularly when combined with adjuvant opioids. 30- and 60-minute pain scores were similar between groups, with both demonstrating clinically significant reduction from baseline. Maternal satisfaction was high across all regimens, with ULC regimens achieving comparable scores. There was no difference in the number of parturients that required rescue top ups between ULC and SC regimens of 0.1% bupivacaine or equivalent.

Rates of spontaneous vaginal delivery ranged from 45.8% to 100%. Caesarean section rates (0–21.6%) were lower in ULC groups across several studies, whereas assisted vaginal delivery rates (0–33%) did not differ significantly. ULC groups were associated with less motor blockade and reduced total local anaesthetic consumption.

Neonatal outcomes, including Apgar scores and umbilical cord pH, were similar between regimens. Adverse maternal effects such as hypotension, nausea, urinary retention and pruritus were infrequent and comparable across groups.

Discussion: ULC regimens are an effective and safe alternative to SC regimens for labour epidural analgesia, providing comparable analgesia and maternal satisfaction with fewer adverse effects, particularly reduced motor blockade. Preservation of motor function facilitates maternal mobility, potentially enhancing patient satisfaction. This advantage aligns with the broader trend in obstetric anaesthesia towards minimizing the impact of epidural analgesia on labour dynamics.

The finding of a higher caesarean section rate in the SC group warrants further investigation. While the association may reflect higher doses of local anaesthetics leading to denser blockade, confounding factors such as study heterogeneity and differences in obstetric practices should be considered. No significant differences were observed in neonatal outcomes or maternal side effects. This indicates that ULC regimens do not compromise maternal or foetal safety.

The heterogeneity across studies in terms of administration methods and outcome reporting is a notable limitation. Administration regimens influence the pharmacokinetics and dynamics of local anaesthetics, potentially affecting efficacy and side effect profiles[2].

In conclusion, this review supports the use of ultra-low concentration local anaesthetic regimens as a safe and effective alternative to standard concentrations for labour epidural analgesia.