Pain Management in Labour – An Obstetrician’s Perspective
03 Mar 2021
byDr. Shek Wan Man Noel
INTRODUCTION
Childbirth is a natural physiological process but it is also considered as one of the most painful experiences in a woman’s life. As such, managing labour pain is one of the major goals in intrapartum care. Women’s experiences of labour pain can vary. They are influenced by emotional, motivational, cognitive, social, and cultural circumstances, as well as previous birth experience.1 The expectation and desire for pain relief vary widely amongst women during labour and delivery. Pain management strategies for women in labour include pharmacological and non-pharmacological options. Pharmacological approaches aim at decreasing or eliminating the physical sensation of labour pain. On the other hand, non-pharmacological approaches are mainly directed at enabling the woman to cope with the pain and maintain a sense of personal control over the birth process, thus minimizing suffering.
PAIN IN LABOUR
Pain originates from different sites during labour and delivery. In the first stage of labour, pain originates from uterine contractions and distension of the cervix and is transmitted via the spinal nerves of T10–L1. Labour pain can be referred to the abdominal wall, lumbosacral region, iliac crests, gluteal areas, and thighs. In the second stage of labour, pain is more intense and also includes pain from distension of vaginal and perineal tissues. The pain signal is transmitted via the pudendal nerve originating from S2–S4 nerve roots. Additionally, the woman experiences rectal pressure and urge to bear down as the presenting part descends into the pelvic outlet.
The International Society of Pain describes pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”.2 While pain is a sensory experience, it is also an emotional experience. Pain scales, eg, visual analogue pain scale, are commonly used to assess the impact of pain interventions. However, the results can be misleading as a woman can rate her pain as severe but can still cope well without suffering. With increasing maternal expectations and a rising trend of advanced care for women in labour, there is a need for evidence-based practices for pain management in labour. It has been reported that healthcare professionals often underestimate the intensity of pain experienced by women in labour and overestimate the relief offered by analgesia provided during labour.3
Non-pharmacological methods
Non-pharmacological methods for managing labour pain are intended to minimize medicalization of labour and avoid the loss of control often experienced following pharmacological analgesia.4 These are generally low risk, easy to institute, and not resource demanding. Moreover, more than one non-pharmacological method can be adopted simultaneously for better pain relief. It also allows flexibility such that the woman can shift to from one method to another when circumstances change. However, the efficacy of these methods is generally difficult to measure and there is insufficient evidence supporting its effectiveness in reducing, moderate-to-severe labour pain.
Childbirth education
Prenatal education varies widely in scope but usually consists of information on normal and complicated labour and birth, common clinical care practices, non-pharmacological and pharmacological pain relief measures, newborn care, infant feeding, and early parenting. Evaluating childbirth education (CBE) outcomes often yield disparate results. Some meta-analyses found little or no improvement in specific birth outcomes for those who attended childbirth classes.5-6 On the other hand, one meta-analysis reported reduced anxiety or fear of childbirth for women who had CBE.7 Despite the lack of evidence of improved birth outcomes with CBE, it remains popular among healthcare professionals as its benefits may extend beyond birth outcomes.
Continuous support in labour
Support persons for labouring woman can include her partner, family or friends, professional support providers (such as doula), and the medical team. It was found that continuous support during labour may improve obstetric outcomes. These include increased spontaneous vaginal birth, shorter duration of labour, and decreased Caesarean birth, instrumental vaginal birth, use of any analgesia, and use of regional analgesia, as well as low five-minute Apgar score and negative feelings about childbirth experiences.8 No evidence of harm was identified with continuous labour support.8
Birthing balls and posture
Use of a birthing ball during labour allows relaxation of the body trunk and pelvic floor while providing some pain relief by allowing mobilization9 or applying pressure on the perineum when used in a sitting position. A randomized controlled trial (n=188) demonstrated 30–40% reduction in labour pain following a birthing ball exercise programme, which also resulted in shorter first stage in labour, less epidural requirement, and fewer Caesarean sections.10 A Cochrane systematic review (n=5,218) showed that walking and an upright position during labour reduced analgesic requirement, shorter first stage of labour, and decrease in Caesarean delivery.9 Another systematic review of 30 trials (n=9,015) demonstrated that upright positions were associated with shorter second stage of labour and fewer instrumental deliveries and episiotomies but increase in blood loss of >500 mL.11
Music and audio analgesia
Music has been used to provide distraction from labour pain and it has been postulated that music reduces anxiety levels and catecholamine production. However, there is insufficient high-quality evidence of its efficacy in managing labour pain, though small trials have reported some reduction in pain and anxiety.12 Audio analgesia is the use of audio stimulation such as music, white noise, or environmental sounds to reduce pain perception. Latest data showed no evidence of benefit in satisfaction with pain relief.12
Aromatherapy
Aromatherapy involves the application of essential oils or essences for inhalation, massaged into the skin, or swallowed as teas or tinctures. It has been suggested that essential oils can increase the production of sedative, stimulant, and relaxing neurotransmitters. Two meta-analyses assessing the efficacy of aromatherapy for labour pain reported no difference in pain intensity, surgical delivery, or the use of pharmacological pain relief.13-14 The results, however, were limited by the small number of trials and patients. On the other hand, a trial using lavender inhalation during labour found significant reduction in pain severity in the first stage of labour compared with a control group. No adverse maternal or foetal impact has been noted.15
Acupressure and acupuncture
Acupressure refers to the application of pressure to specific areas of the body, whereas acupuncture refers to the insertion of fine needles in similar areas. It is believed that these techniques work by stimulating touch fibres, which in turn block pain impulses at the “pain gates” within the spinal cord and the modification of endorphin release. A previous meta-analysis demonstrated significantly reduced pain intensity in the acupressure group compared with the placebo group (light touch) or combined group (light touch or no treatment). However, there were no marked differences in the use of pharmacological analgesia.16 Furthermore, a systematic review of nine randomized trials involving approximately 1,550 women concluded that acupuncture may increase satisfaction with pain relief and reduce the use of pharmacological pain relief.17
Transcutaneous electric nerve stimulation
Transcutaneous electric nerve stimulation (TENS) is the application of low-voltage electrical impulses from a handheld device to the skin via surface electrodes. It is usually applied to the lower back (T10–S2). The mechanism of action is not well understood but it is believed that electrical impulses block transmission of pain impulses within the spinal cord and also facilitate release of endorphins, which mediate pain perception.3 TENS allows a labouring woman to control her pain relief by adjusting the intensity and frequency of electrical impulses delivered. A Cochrane review of 17 trials including over 1,400 women showed that there was no difference in pain scores between TENS recipients and controls. Interestingly, the placebo group also reported wanting to use the placebo again, illustrating that rather than the device, it is the element of control may be more of a benefit.18 No adverse events were reported.
Water immersion
Warm water immersion, deep enough to cover the abdomen, is thought to encourage relaxation and reduce labour pain.19 A meta-analysis of randomized trials evaluating the safety and efficacy of water immersion during the first stage of labour demonstrated a slightly lower use of epidural, spinal, and paracervical analgesia.20 The optimal time to initiate water immersion during the course of labour is unknown. Also, prolonged immersion of >2 hours has been reported to suppress oxytocin production, resulting in prolonged labour.21
Sterile water injection
Sterile water (0.05–0.1 mL) is injected subcutaneously or intracutaneously into the area of the lumbosacral spine to form small papules. Four to six injections are usually done. The exact mechanism is not well understood and the hypothesis is based on the gate control theory of pain. A Cochrane systematic review of seven trials (n=766) reported a significant reduction in pain scores with sterile water injection compared with placebo injection.22
Hypnosis
Hypnosis or hypnobirthing refers to directing the attention in labour to calm and comforting influences, thereby increasing a woman’s receptivity to positive “suggestions”, and reducing awareness of external stimuli. It is either delivered by a hypnotherapist or the woman herself. In a meta-analysis of nine trials including nearly 3,000 subjects, women receiving hypnotherapy were less likely to use pharmacological pain relief (excluding epidural) than those in the control group, but there was no difference in the sense of coping with labour, satisfaction with pain relief, or spontaneous vaginal birth.23
Biofeedback
Biofeedback is a form of behavioural therapy training for the woman to gain control over physiological responses with the aid of electronic instruments. It aims to facilitate the woman to consciously regulate both psychological and physical processes such as pain. A systematic review of four trials (n=186) assessing the electromyographic biofeedback reported some positive effects early in labour but there was no difference between the biofeedback and control group in terms of use of pharmacological pain relief, augmentation of labour, instrumental, or Caesarean delivery.24
Breathing techniques and relaxation
Relaxation training, which comes in various forms of techniques, has been reported to result in reduced pain during the latent phase of labour.12 Rhythmic breathing promotes relaxation and provides distraction from labour pain.
PHARMACOLOGICAL METHODS
Pharmacological options mostly have dose-dependent maternal and foetal adverse effects, and large cumulative doses may be required when used in labour. Neuraxial labour analgesia (eg, epidural and combined spinal-epidural) is a subset of pharmacological pain management. It provides more consistently effective labour pain analgesia than other options.
Nitrous oxide (gas and air)
Nitrous oxide acts as a very weak anaesthetic at high concentrations and as an analgesic and anxiolytic at lower concentrations.3 It is usually a blend of 50% nitrous oxide and 50% oxygen. Nitrous oxide has a short half-life of 2–3 minutes and is rapidly cleared via the lungs. It does not affect the foetal heart rate or respiratory rate of the newborn. A systematic review showed that nitrous oxide was effective in reducing pain intensity and providing pain relief in labour.25 However, substantial heterogeneity was detected for pain intensity and it was also associated with more side effects such as nausea, vomiting, dizziness, and drowsiness.25
Non-opioid analgesics
The literature studying the efficacy of paracetamol, non-steroidal anti-inflammatory drugs, antispasmodics, antihistamines, and sedatives are limited. A previous review demonstrated that there is insufficient evidence to support a role for non-opioid drugs on their own to manage pain during labour.26
Opioids
Dihydrocodeine, pethidine, diamorphine, fentanyl, and remifentanil are commonly used opioids. They have the advantages of ease of administration, wide availability, lower cost, and are less invasive than neuraxial techniques. Intramuscular pethidine is most commonly used and midwives are licensed to prescribe and administer the drug in most countries. Adverse effects of opioids include drowsiness, hypoventilation, nausea, vomiting, and increase in gastrointestinal transit time. They can cross the placenta and some are trapped by ionization. In utero manifestations include reduced foetal heart rate variability and, in the neonate, respiratory depression, and neurobehavioral changes. A Cochrane systematic review found that parental opioids, including intramuscular, intravenous, and patient-controlled analgesia (PCA), provided some labour pain relief and moderate satisfaction with analgesia, although up to two-thirds of women reported moderate or severe pain within 1–2 hours after administration.27
PCA allows the patient to self-administer a programmed dose of intravenous medication with lockout intervals between doses. It offers an alternative and effective option when neuraxial analgesia is contraindicated, unsuccessful, or unavailable. Apart from allowing a sense of control for the labouring woman, PCA offers rapid onset of analgesia, better control of pain relative to side effects than intermittent parental opioid injection.28 Short-acting opioids are preferred in PCA to allow rapid changes in plasma levels to match the changing analgesic need. Remifentanil has a rapid onset, ultrashort duration, and is metabolized rapidly by tissue esterases in both the mother and foetus, hence it is a common PCA choice for labour pain management. Remifentanil PCA is less effective than neuraxial analgesia but more effective than long-acting opioid analgesia or nitrous oxide.28-29 However, remifentanil is associated with respiratory depression.30-31 There have been several reported cases of respiratory and cardiac arrest following the use of remifentanil.32-33 It is recommended that women who receive remifentanil PCA should be monitored with continuous pulse oximetry and one-to-one nursing, and to avoid background infusion or other concomitant analgesic use. Moreover, a maximum bolus dose of 30 mcg should be used, with lockout interval of 2 minutes.30-31,34
REGIONAL ANALGESIA
Pudendal and paracervical blocks
Pudendal and paracervical blocks are single-injection nerve blocks involving a one-time injection of local anaesthetic adjacent to the nerve or plexus. These are commonly administered by obstetricians rather than anaesthesiologists. Based on a systematic review of limited fair-quality trials, local anaesthetic nerve blocks may be more effective than placebo and opioid and non-opioid analgesia for pain management in labour.35
Bilateral pudendal nerve blocks are useful to alleviate pain arising from vaginal and perineal distension during the second stage of labour.36 They may be used as a supplement for epidural analgesia if the sacral nerves are not adequately anaesthetized. They may be performed for low-forceps delivery but are inadequate for mid-forceps delivery.
A paracervical block can be used to reduce pain associated with cervical dilation during the active phase of labour when alternative pain management options are not available. It is not effective in the second stage of labour because sensory nerves from the perineum are not blocked. It is also associated with incidences of foetal bradycardia.
Neuraxial analgesia
Neuraxial analgesia is the most effective means of labour pain management.36 It is appropriate for labouring women regardless of parity and stages of labour unless delivery is imminent, except when there is a contraindication. The techniques are usually easily performed, life-threatening complications are rare, and side effects such as pruritus and hypotension are transient and easily treated. Epidural and combined spinal-epidural (CSE) analgesia are the most commonly used neuraxial techniques for labour pain management. Single shot and continuous spinal techniques, which provide more rapid onset of symmetric analgesia than epidural, may be used in selected scenarios. Contraindications for epidural are outlined in Table 1.
Epidural analgesia involves the injection of local anaesthetics with or without an opioid into the epidural space to produce a reversible loss of sensation and motor function. It provides better pain relief than all other forms of labour analgesia and reduces the need for additional pain relief but does not increase maternal satisfaction with pain relief.36 On the other hand, when compared with women using opioids, it is associated with prolonged second stage of labour and increased instrumental delivery rates.36-37 However, there is no association found with prolonged first stage of labour, increased risk of Caesarean section, or long-term back problems.37 Epidural analgesia reduces the risk of foetal acidosis and need for naloxone administration compared with opioids.37 Recently, using lower concentrations of local anaesthetics in combination with opioids has immensely reduced adverse effects, including less impairment of motor function, to even allowing walking during labour, ability to bear down, and also reduces hypotension. Maintenance of epidural analgesia in labour is administered by an infusion pump, given by continuous infusion, by patient-controlled epidural analgesia (PCEA) with or without background continuous infusion, or by programmed intermittent bolus with or without clinician-administered boluses for breakthrough pain. PCEA allows the woman to be in control of her pain by self-administered top-ups according to her need during labour. It involves the use of pre-programmed pumps with a set dose and lockout interval (usually 30 minutes) to avoid high blocks and toxicity. A meta-analysis found that PCEA was associated with lower local anaesthetic consumption, less motor blockade, and lower incidence of breakthrough pain compared with continuous infusion analgesia.38
CSE requires intrathecal injection of local anaesthetic with or without opioids to initiate spinal analgesia and the insertion of an epidural catheter to allow maintenance of analgesia or conversion to surgical anaesthesia. The main advantages are a rapid onset compared with conventional epidural, and it allows the option to continue analgesia throughout labour and delivery and provides a means of rapid conversion to surgical anaesthesia when necessary through the epidural catheter. A meta-analysis comparing CSE with epidural analgesia showed maternal satisfaction. It also revealed that Caesarean section rates and mobility were also similar but with adverse effects, such as pruritus.39 There was no difference in obstetric or neonatal outcomes.
CONCLUSION
Labour pain is dynamic and associated with multiple factors. This article has discussed the main analgesic options. It is key to providing appropriate information to pregnant and labouring women about pain management options in labour. Table 2 summarizes the evidence for the analgesic options. Interestingly, lower level of labour pain has been associated with a higher level of childbirth satisfaction, but a higher level of labour pain does not preclude an overall satisfying experience. While epidural analgesia seems to provide the best pain relief overall, there is no difference in maternal satisfaction compared with the other options.36 A sense of personal control in association with participation in the informed decision-making processes in labour has been demonstrated to correlate with overall maternal satisfaction with childbirth.40 Healthcare providers play an important role to facilitate labouring women to develop an individualized pain management regimen such that the birthing experience is pleasant and memorable with optimal outcomes.
About the author
Dr Shek Wan Man Noel is Consultant and Honorary Clinical Associate Professor in the Department of Obstetrics and Gynaecology at Queen Mary Hospital, The University of Hong Kong, Hong Kong, SAR, China. Conflict of interest: None.
Childbirth is a natural physiological process but it is also considered as one of the most painful experiences in a woman’s life. As such, managing labour pain is one of the major goals in intrapartum care. Women’s experiences of labour pain can vary. They are influenced by emotional, motivational, cognitive, social, and cultural circumstances, as well as previous birth experience.1 The expectation and desire for pain relief vary widely amongst women during labour and delivery. Pain management strategies for women in labour include pharmacological and non-pharmacological options. Pharmacological approaches aim at decreasing or eliminating the physical sensation of labour pain. On the other hand, non-pharmacological approaches are mainly directed at enabling the woman to cope with the pain and maintain a sense of personal control over the birth process, thus minimizing suffering.
PAIN IN LABOUR
Pain originates from different sites during labour and delivery. In the first stage of labour, pain originates from uterine contractions and distension of the cervix and is transmitted via the spinal nerves of T10–L1. Labour pain can be referred to the abdominal wall, lumbosacral region, iliac crests, gluteal areas, and thighs. In the second stage of labour, pain is more intense and also includes pain from distension of vaginal and perineal tissues. The pain signal is transmitted via the pudendal nerve originating from S2–S4 nerve roots. Additionally, the woman experiences rectal pressure and urge to bear down as the presenting part descends into the pelvic outlet.
The International Society of Pain describes pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”.2 While pain is a sensory experience, it is also an emotional experience. Pain scales, eg, visual analogue pain scale, are commonly used to assess the impact of pain interventions. However, the results can be misleading as a woman can rate her pain as severe but can still cope well without suffering. With increasing maternal expectations and a rising trend of advanced care for women in labour, there is a need for evidence-based practices for pain management in labour. It has been reported that healthcare professionals often underestimate the intensity of pain experienced by women in labour and overestimate the relief offered by analgesia provided during labour.3
Non-pharmacological methods
Non-pharmacological methods for managing labour pain are intended to minimize medicalization of labour and avoid the loss of control often experienced following pharmacological analgesia.4 These are generally low risk, easy to institute, and not resource demanding. Moreover, more than one non-pharmacological method can be adopted simultaneously for better pain relief. It also allows flexibility such that the woman can shift to from one method to another when circumstances change. However, the efficacy of these methods is generally difficult to measure and there is insufficient evidence supporting its effectiveness in reducing, moderate-to-severe labour pain.
Childbirth education
Prenatal education varies widely in scope but usually consists of information on normal and complicated labour and birth, common clinical care practices, non-pharmacological and pharmacological pain relief measures, newborn care, infant feeding, and early parenting. Evaluating childbirth education (CBE) outcomes often yield disparate results. Some meta-analyses found little or no improvement in specific birth outcomes for those who attended childbirth classes.5-6 On the other hand, one meta-analysis reported reduced anxiety or fear of childbirth for women who had CBE.7 Despite the lack of evidence of improved birth outcomes with CBE, it remains popular among healthcare professionals as its benefits may extend beyond birth outcomes.
Continuous support in labour
Support persons for labouring woman can include her partner, family or friends, professional support providers (such as doula), and the medical team. It was found that continuous support during labour may improve obstetric outcomes. These include increased spontaneous vaginal birth, shorter duration of labour, and decreased Caesarean birth, instrumental vaginal birth, use of any analgesia, and use of regional analgesia, as well as low five-minute Apgar score and negative feelings about childbirth experiences.8 No evidence of harm was identified with continuous labour support.8
Birthing balls and posture
Use of a birthing ball during labour allows relaxation of the body trunk and pelvic floor while providing some pain relief by allowing mobilization9 or applying pressure on the perineum when used in a sitting position. A randomized controlled trial (n=188) demonstrated 30–40% reduction in labour pain following a birthing ball exercise programme, which also resulted in shorter first stage in labour, less epidural requirement, and fewer Caesarean sections.10 A Cochrane systematic review (n=5,218) showed that walking and an upright position during labour reduced analgesic requirement, shorter first stage of labour, and decrease in Caesarean delivery.9 Another systematic review of 30 trials (n=9,015) demonstrated that upright positions were associated with shorter second stage of labour and fewer instrumental deliveries and episiotomies but increase in blood loss of >500 mL.11
Music and audio analgesia
Music has been used to provide distraction from labour pain and it has been postulated that music reduces anxiety levels and catecholamine production. However, there is insufficient high-quality evidence of its efficacy in managing labour pain, though small trials have reported some reduction in pain and anxiety.12 Audio analgesia is the use of audio stimulation such as music, white noise, or environmental sounds to reduce pain perception. Latest data showed no evidence of benefit in satisfaction with pain relief.12
Aromatherapy
Aromatherapy involves the application of essential oils or essences for inhalation, massaged into the skin, or swallowed as teas or tinctures. It has been suggested that essential oils can increase the production of sedative, stimulant, and relaxing neurotransmitters. Two meta-analyses assessing the efficacy of aromatherapy for labour pain reported no difference in pain intensity, surgical delivery, or the use of pharmacological pain relief.13-14 The results, however, were limited by the small number of trials and patients. On the other hand, a trial using lavender inhalation during labour found significant reduction in pain severity in the first stage of labour compared with a control group. No adverse maternal or foetal impact has been noted.15
Acupressure and acupuncture
Acupressure refers to the application of pressure to specific areas of the body, whereas acupuncture refers to the insertion of fine needles in similar areas. It is believed that these techniques work by stimulating touch fibres, which in turn block pain impulses at the “pain gates” within the spinal cord and the modification of endorphin release. A previous meta-analysis demonstrated significantly reduced pain intensity in the acupressure group compared with the placebo group (light touch) or combined group (light touch or no treatment). However, there were no marked differences in the use of pharmacological analgesia.16 Furthermore, a systematic review of nine randomized trials involving approximately 1,550 women concluded that acupuncture may increase satisfaction with pain relief and reduce the use of pharmacological pain relief.17
Transcutaneous electric nerve stimulation
Transcutaneous electric nerve stimulation (TENS) is the application of low-voltage electrical impulses from a handheld device to the skin via surface electrodes. It is usually applied to the lower back (T10–S2). The mechanism of action is not well understood but it is believed that electrical impulses block transmission of pain impulses within the spinal cord and also facilitate release of endorphins, which mediate pain perception.3 TENS allows a labouring woman to control her pain relief by adjusting the intensity and frequency of electrical impulses delivered. A Cochrane review of 17 trials including over 1,400 women showed that there was no difference in pain scores between TENS recipients and controls. Interestingly, the placebo group also reported wanting to use the placebo again, illustrating that rather than the device, it is the element of control may be more of a benefit.18 No adverse events were reported.
Water immersion
Warm water immersion, deep enough to cover the abdomen, is thought to encourage relaxation and reduce labour pain.19 A meta-analysis of randomized trials evaluating the safety and efficacy of water immersion during the first stage of labour demonstrated a slightly lower use of epidural, spinal, and paracervical analgesia.20 The optimal time to initiate water immersion during the course of labour is unknown. Also, prolonged immersion of >2 hours has been reported to suppress oxytocin production, resulting in prolonged labour.21
Sterile water injection
Sterile water (0.05–0.1 mL) is injected subcutaneously or intracutaneously into the area of the lumbosacral spine to form small papules. Four to six injections are usually done. The exact mechanism is not well understood and the hypothesis is based on the gate control theory of pain. A Cochrane systematic review of seven trials (n=766) reported a significant reduction in pain scores with sterile water injection compared with placebo injection.22
Hypnosis
Hypnosis or hypnobirthing refers to directing the attention in labour to calm and comforting influences, thereby increasing a woman’s receptivity to positive “suggestions”, and reducing awareness of external stimuli. It is either delivered by a hypnotherapist or the woman herself. In a meta-analysis of nine trials including nearly 3,000 subjects, women receiving hypnotherapy were less likely to use pharmacological pain relief (excluding epidural) than those in the control group, but there was no difference in the sense of coping with labour, satisfaction with pain relief, or spontaneous vaginal birth.23
Biofeedback
Biofeedback is a form of behavioural therapy training for the woman to gain control over physiological responses with the aid of electronic instruments. It aims to facilitate the woman to consciously regulate both psychological and physical processes such as pain. A systematic review of four trials (n=186) assessing the electromyographic biofeedback reported some positive effects early in labour but there was no difference between the biofeedback and control group in terms of use of pharmacological pain relief, augmentation of labour, instrumental, or Caesarean delivery.24
Breathing techniques and relaxation
Relaxation training, which comes in various forms of techniques, has been reported to result in reduced pain during the latent phase of labour.12 Rhythmic breathing promotes relaxation and provides distraction from labour pain.
PHARMACOLOGICAL METHODS
Pharmacological options mostly have dose-dependent maternal and foetal adverse effects, and large cumulative doses may be required when used in labour. Neuraxial labour analgesia (eg, epidural and combined spinal-epidural) is a subset of pharmacological pain management. It provides more consistently effective labour pain analgesia than other options.
Nitrous oxide (gas and air)
Nitrous oxide acts as a very weak anaesthetic at high concentrations and as an analgesic and anxiolytic at lower concentrations.3 It is usually a blend of 50% nitrous oxide and 50% oxygen. Nitrous oxide has a short half-life of 2–3 minutes and is rapidly cleared via the lungs. It does not affect the foetal heart rate or respiratory rate of the newborn. A systematic review showed that nitrous oxide was effective in reducing pain intensity and providing pain relief in labour.25 However, substantial heterogeneity was detected for pain intensity and it was also associated with more side effects such as nausea, vomiting, dizziness, and drowsiness.25
Non-opioid analgesics
The literature studying the efficacy of paracetamol, non-steroidal anti-inflammatory drugs, antispasmodics, antihistamines, and sedatives are limited. A previous review demonstrated that there is insufficient evidence to support a role for non-opioid drugs on their own to manage pain during labour.26
Opioids
Dihydrocodeine, pethidine, diamorphine, fentanyl, and remifentanil are commonly used opioids. They have the advantages of ease of administration, wide availability, lower cost, and are less invasive than neuraxial techniques. Intramuscular pethidine is most commonly used and midwives are licensed to prescribe and administer the drug in most countries. Adverse effects of opioids include drowsiness, hypoventilation, nausea, vomiting, and increase in gastrointestinal transit time. They can cross the placenta and some are trapped by ionization. In utero manifestations include reduced foetal heart rate variability and, in the neonate, respiratory depression, and neurobehavioral changes. A Cochrane systematic review found that parental opioids, including intramuscular, intravenous, and patient-controlled analgesia (PCA), provided some labour pain relief and moderate satisfaction with analgesia, although up to two-thirds of women reported moderate or severe pain within 1–2 hours after administration.27
PCA allows the patient to self-administer a programmed dose of intravenous medication with lockout intervals between doses. It offers an alternative and effective option when neuraxial analgesia is contraindicated, unsuccessful, or unavailable. Apart from allowing a sense of control for the labouring woman, PCA offers rapid onset of analgesia, better control of pain relative to side effects than intermittent parental opioid injection.28 Short-acting opioids are preferred in PCA to allow rapid changes in plasma levels to match the changing analgesic need. Remifentanil has a rapid onset, ultrashort duration, and is metabolized rapidly by tissue esterases in both the mother and foetus, hence it is a common PCA choice for labour pain management. Remifentanil PCA is less effective than neuraxial analgesia but more effective than long-acting opioid analgesia or nitrous oxide.28-29 However, remifentanil is associated with respiratory depression.30-31 There have been several reported cases of respiratory and cardiac arrest following the use of remifentanil.32-33 It is recommended that women who receive remifentanil PCA should be monitored with continuous pulse oximetry and one-to-one nursing, and to avoid background infusion or other concomitant analgesic use. Moreover, a maximum bolus dose of 30 mcg should be used, with lockout interval of 2 minutes.30-31,34
REGIONAL ANALGESIA
Pudendal and paracervical blocks
Pudendal and paracervical blocks are single-injection nerve blocks involving a one-time injection of local anaesthetic adjacent to the nerve or plexus. These are commonly administered by obstetricians rather than anaesthesiologists. Based on a systematic review of limited fair-quality trials, local anaesthetic nerve blocks may be more effective than placebo and opioid and non-opioid analgesia for pain management in labour.35
Bilateral pudendal nerve blocks are useful to alleviate pain arising from vaginal and perineal distension during the second stage of labour.36 They may be used as a supplement for epidural analgesia if the sacral nerves are not adequately anaesthetized. They may be performed for low-forceps delivery but are inadequate for mid-forceps delivery.
A paracervical block can be used to reduce pain associated with cervical dilation during the active phase of labour when alternative pain management options are not available. It is not effective in the second stage of labour because sensory nerves from the perineum are not blocked. It is also associated with incidences of foetal bradycardia.
Neuraxial analgesia
Neuraxial analgesia is the most effective means of labour pain management.36 It is appropriate for labouring women regardless of parity and stages of labour unless delivery is imminent, except when there is a contraindication. The techniques are usually easily performed, life-threatening complications are rare, and side effects such as pruritus and hypotension are transient and easily treated. Epidural and combined spinal-epidural (CSE) analgesia are the most commonly used neuraxial techniques for labour pain management. Single shot and continuous spinal techniques, which provide more rapid onset of symmetric analgesia than epidural, may be used in selected scenarios. Contraindications for epidural are outlined in Table 1.
Epidural analgesia involves the injection of local anaesthetics with or without an opioid into the epidural space to produce a reversible loss of sensation and motor function. It provides better pain relief than all other forms of labour analgesia and reduces the need for additional pain relief but does not increase maternal satisfaction with pain relief.36 On the other hand, when compared with women using opioids, it is associated with prolonged second stage of labour and increased instrumental delivery rates.36-37 However, there is no association found with prolonged first stage of labour, increased risk of Caesarean section, or long-term back problems.37 Epidural analgesia reduces the risk of foetal acidosis and need for naloxone administration compared with opioids.37 Recently, using lower concentrations of local anaesthetics in combination with opioids has immensely reduced adverse effects, including less impairment of motor function, to even allowing walking during labour, ability to bear down, and also reduces hypotension. Maintenance of epidural analgesia in labour is administered by an infusion pump, given by continuous infusion, by patient-controlled epidural analgesia (PCEA) with or without background continuous infusion, or by programmed intermittent bolus with or without clinician-administered boluses for breakthrough pain. PCEA allows the woman to be in control of her pain by self-administered top-ups according to her need during labour. It involves the use of pre-programmed pumps with a set dose and lockout interval (usually 30 minutes) to avoid high blocks and toxicity. A meta-analysis found that PCEA was associated with lower local anaesthetic consumption, less motor blockade, and lower incidence of breakthrough pain compared with continuous infusion analgesia.38
CSE requires intrathecal injection of local anaesthetic with or without opioids to initiate spinal analgesia and the insertion of an epidural catheter to allow maintenance of analgesia or conversion to surgical anaesthesia. The main advantages are a rapid onset compared with conventional epidural, and it allows the option to continue analgesia throughout labour and delivery and provides a means of rapid conversion to surgical anaesthesia when necessary through the epidural catheter. A meta-analysis comparing CSE with epidural analgesia showed maternal satisfaction. It also revealed that Caesarean section rates and mobility were also similar but with adverse effects, such as pruritus.39 There was no difference in obstetric or neonatal outcomes.
CONCLUSION
Labour pain is dynamic and associated with multiple factors. This article has discussed the main analgesic options. It is key to providing appropriate information to pregnant and labouring women about pain management options in labour. Table 2 summarizes the evidence for the analgesic options. Interestingly, lower level of labour pain has been associated with a higher level of childbirth satisfaction, but a higher level of labour pain does not preclude an overall satisfying experience. While epidural analgesia seems to provide the best pain relief overall, there is no difference in maternal satisfaction compared with the other options.36 A sense of personal control in association with participation in the informed decision-making processes in labour has been demonstrated to correlate with overall maternal satisfaction with childbirth.40 Healthcare providers play an important role to facilitate labouring women to develop an individualized pain management regimen such that the birthing experience is pleasant and memorable with optimal outcomes.
About the author
Dr Shek Wan Man Noel is Consultant and Honorary Clinical Associate Professor in the Department of Obstetrics and Gynaecology at Queen Mary Hospital, The University of Hong Kong, Hong Kong, SAR, China. Conflict of interest: None.
Resources
JPOG 202101 CME HK
JPOG 202101 CME HK