Advances in modern medicine during the 20th century have revolutionised the ability to provide safe and effective analgesia for women during labour. The pain associated with labour and childbirth is recognised as potentially the most significant a patient may ever endure. It is a true marvel of medicine that we now have the ability to mitigate this pain in a safe and controlled manner.

Analgesic strategies and preferences vary between different individuals and cultures. A variety of factors will determine which strategies are used, including access to specialised medical resources, individual choice, societal expectations and cultural factors. As medical practitioners, it is important to consider these issues and to balance them in the context of the best evidence-based therapies that we have in our armamentarium.

This article seeks to outline the common analgesic strategies available to healthcare providers in the context of the labouring woman for childbirth, with reference to the most up-to-date evidence.

Background

The level of pain experienced, and the effectiveness of pain relief used, can significantly influence the woman’s overall satisfaction with her labour and the birth. This has the potential to yield long-term emotional and psychological sequelae.¹

Women experience varying degrees of pain in labour and exhibit an equally varying range of responses to it. A woman’s experience of the pain of labour can be influenced by her individual circumstances, the environment she is in, her cultural background, previous preparation and education of the process of labour and the support networks available to her during the labour itself.^{2 3}

The requirement for pain relief is also influenced by the type of onset of labour (spontaneous versus induced), the augmentation and duration of labour, as well as complicating factors such as fetal presentation, obstructed labour and the need for medical interventions such as instrumental vaginal delivery and episiotomy.

Available strategies

We can split the available options for pain relief in labour into:

• Non-pharmacological techniques
• Pharmacological techniques

Regardless of the technique used for each individual’s circumstance, it is important that it is both effective and safe for both the mother and baby.

Non-pharmacological techniques

A variety of non-pharmacological methods, with varying degrees of supporting evidence, have been summarised in the literature.^{4 5}  These may have benefit for different individuals based on their personal preferences or cultural beliefs.

It is important for medical practitioners and caregivers to understand these strategies, appreciate their benefits but also the inherent limitations with what can be potentially less definitive analgesia. Education and informed consent for the patient is of primary importance. Brief points on these techniques include:

Relaxation therapies

• use one’s emotional coping mechanisms to help better manage pain

Hypnosis

• involves the patient entering a hypnotic state under supervision from a trained therapist to gain better control over pain

Continuous support

• requires a trained support person to improve the psychological experience of labour
• evidence shows these patients are less likely to have pain relief in labour and be more satisfied with their experience

Acupuncture

• stimulates specific points on the body with fine needles that may inhibit pain signal transmission +/- release natural endorphin

Massage and reflexology

• inhibits pain transmission, provides support and also distraction, with data showing physical and emotional benefits

TENS

• based on the ‘gate-theory’, it is non-invasive and easy to use
• a systematic review of eight RCTs failed to demonstrate significant analgesic effect⁵

Immersion

• the sensation of warm water is postulated to inhibit pain signals as well as support the gravid uterus

Intradermal injection of sterile water

• involves the injection of 0.1ml sterile water in four points over the sacrum
• potential reduction in pain during labour but other evidence shows women do not rate it as effective as other analgesic strategies

Reported effectiveness of the above techniques varies between different studies. Strategies such as immersion, massage, acupuncture and hypnosis may be helpful therapies for pain management in labour. Other techniques such as aromatherapy and homeopathy may have a role for some patients, but no data has demonstrated definitive benefit.

Pharmacological techniques

Pharmacological analgesic methods include inhalation of nitrous oxide, parenteral opioids and also regional anaesthesia in the form of epidural and combined-spinal-epidural during labour. Non-regional analgesia in labour remains the most frequently used method worldwide.

1. Inhalational methods

Entonox

Nitrous oxide/oxygen mixtures have been used in obstetric practice since 1880. Entonox (50% nitrous oxide in oxygen) is located ubiquitously in obstetric units throughout the world and has a long track record of safety for the labouring parturient. 53% of labouring women used this form of analgesia in Australia in 2018.⁶

Nitrous oxide has a low blood gas solubility, meaning it rapidly equilibrates with blood, is rapidly washed-in during use and rapidly washed-out when ceased. The technique of use is important, with around 10 full breaths or 50 seconds breathing required to achieve maximum effect.

A Cochrane review in 2012 demonstrated that Entonox provided better pain relief than placebo, but was associated with more drowsiness, dizziness, nausea and vomiting. There were no differences in in Apgar scores or caesarean rates between people who used Entonox and those who had a placebo or no treatment.

Other studies have shown more limited benefit with Entonox and it is postulated that even though analgesia may not be significantly improved, maternal satisfaction may be maintained or improved with this technique as it enables the patient to control their own analgesia.

2. Opioids

Pethidine

Pethidine has a long history of use and is the most widely used and investigated opioid. Its typically administered analgesic dose is 1mg/kg IM. Studies have shown midwives rated the efficacy of pethidine more than the women receiving it and it is thought that this may be attributable to some of the side effects for the patient of loss of control, confusion and sedation.⁵  It also causes dose-dependent respiratory depression and hypoventilation.

Pethidine rapidly crosses the placenta and the highest fetal plasma concentrations occur 2–3 hours after maternal administration. Respiratory depression is more likely in the neonate due to immature respiratory centres, greater free-drug concentration and ion trapping.

Morphine

Morphine is another commonly used parenteral opioid that has widespread use for labour analgesia. The dose used is titrated at 2.5–5mg IV or 5–10mg IM. The side effects for morphine are dose-dependent and similar to pethidine, although morphine metabolites do not have convulsant effects like those of pethidine. Morphine rapidly crosses the placenta but rapid maternal elimination results in lower fetal drug load.

Remifentanil PCA

Remifentanil patient-controlled analgesia (PCA) is an ultra-short-acting opioid derivative of fentanyl with strong analgesic properties that is rapidly metabolised by red blood cell and tissue esterases. These enzymes are non-saturable, so the drug is short-acting and does not accumulate over time.

Remifentanil PCA is a useful alternative for the labouring parturient when more definitive strategies such as regional analgesia are unavailable or contraindicated. It is does require a higher degree of monitoring, expert midwifery and close medical supervision during set up and ongoing use, to ensure safety.

A typical regimen involves a 30µg IV bolus of remifentanil delivered over 60 seconds with a two-minute lockout from a dedicated, programmed pump device. Remifentanil PCA has demonstrated good neonatal outcomes, moderate analgesic effect and high degrees of patient satisfaction.

3. Regional techniques

Epidural analgesia

Epidural analgesia is a nerve blockade technique that involves siting an epidural catheter via Tuohy needle into the epidural space of the lower lumbar region of the spine and the subsequent injection of local anaesthetic (with or without adjuncts such as fentanyl).

The local anaesthetic is delivered close to the spinal nerves that normally transmit painful stimuli from the contracting uterus (visceral pain) and vaginal canal (visceral and somatic pain). Local anaesthetic inhibits nerve conduction by blocking sodium channels in nerve membranes, thereby preventing the propagation of signals along these nerve fibres to the central nervous system, thus aiming to render the woman more comfortable during her labour.

Epidural analgesia was first used in obstetric practice in 1946 and its use in labour has increased in recent decades with around 40% of women choosing it in Australia in 2018.⁶

Epidural local anaesthetic solutions are administered either by bolus, continuous infusion or via patient-controlled pumps. Boluses of higher concentrations of local anaesthetic, as used in the earlier years, have been associated with more dense motor block resulting in reduced mobility, decreased pelvic tone and loss of the bearing-down sensations usually experienced in the second stage of labour.

More recently, a trend to use a lower concentration of local anaesthetic in combination with opioid has seen effective analgesia maintained and also preserved a greater degree of motor function. This enables the patient to move her legs more freely and also preserves her ability to bear down and avoid an assisted vaginal birth, such as the use of forceps.

Combined spinal-epidural analgesia

Combined spinal-epidural (CSE) involves a single injection of local anaesthetic (with or without fentanyl) into the subarachnoid space, as well as subsequent insertion of an epidural catheter.

CSE combines the advantages of spinal analgesia (faster onset of pain relief from the time of injection and more reliable analgesia), with the advantages of epidural analgesia where continuing analgesia is maintained through the remaining duration of labour.

Brief summary of recent evidence

A Cochrane Review⁷ in 2018 set out to assess the effectiveness of all kinds of epidural analgesia (including CSE) on the mother and the baby, when compared with non-epidural or no pain relief during labour. They assessed over 40 trials involving more than 11,000 women that contributed information to the review.

Key Findings⁷

• Low-quality evidence shows that epidural analgesia may be more effective in reducing pain during labour (as expressed by lower pain scores) and increases maternal satisfaction with pain relief compared to other, non-epidural methods
• Early studies demonstrated some women who have an epidural instead of opioid analgesia may be more likely to have an assisted vaginal birth; however, this effect was not seen in studies conducted after 2005, where the use of lower concentrations of local anaesthetic and more modern epidural techniques such as patient-controlled epidural analgesia have been introduced
• Epidural analgesia had no impact on the risk of caesarean section or incidence of long-term backache and did not appear to have an immediate effect on neonatal status (as determined by Apgar scores) or in admissions to neonatal intensive care
• Side effects were reported in patients with epidural, including more hypotension, motor blockade, fever and urinary retention
• Patients with an epidural also endured longer first and second stages of labour, and were more likely to have oxytocin augmentation than women in opioid analgesia groups

Conclusion

Labour and childbirth, in the absence of analgesia, has the potential to be one of the most painful experiences a woman may endure in her lifetime.

Certainly, childbirth should be an extremely rewarding experience. Balancing the needs and expectations of each individual with effective analgesic strategies to ensure safety, maintain satisfaction and to optimise the overall experience for the patient, is important

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6. Australian Institute of Health and Welfare 2020. Australia’s mothers and babies 2018: in brief. Perinatal statistics series no. 36. Cat. no. PER 108. Canberra: AIHW.
7. Anim-Somuah M, Smyth RMD, Cyna AM. Epidural versus non-epidural or no analgesia for pain management in labour. Cochrane Database Syst Rev. 2018;5:CD000331.