Analgesia, Anaesthesia and Pregnancy. 4th Ed. Róisín Monteiro

Chapter 26. Epidural analgesia for labour

The caudal route was the first approach used for epidural analgesia and anaesthesia in childbirth and was described in 1901. It has now been superseded by the lumbar route, with continuous lumbar epidural analgesia for labour described in the 1940s.

The use of epidural analgesia varies widely between different units in the UK, some small units having no provision and others having an epidural rate of over 50%.

It is generally accepted that epidural analgesia provides the most consistently effective form of pain relief during labour, and there are other benefits such as the ability to top up for instrumental delivery or caesarean section, and an improved fetal acid-base status if the mother is exhausted. Conversely, side effects and complications do exist, and the provision of a 24-hour epidural service is expensive. There are therefore differing (and often strong) views on the place of epidural analgesia in labour, held by mothers, midwives, obstetricians and obstetric anaesthetists.

Contraindications

The contraindications of epidural analgesia are the same as those in the non-pregnant population, but in the context of the above benefits, especially avoidance of general anaesthesia if an epidural catheter is in situ. The most common reasons for being unable to recommend epidural analgesia are coagulation disorders (whether iatrogenic or pathological), sepsis (local or systemic), and spinal neurological abnormality or the presence of metal or other implants around the lumbar region.

Consent

The modern emphasis on informed consent and the placement of mothers at the centre of their care have highlighted the difficulties that can exist when providing epidural analgesia for labour. There are many factors that may impair the usual consenting process, both antenatally and during labour itself; these are discussed further in Chapter 169, Consent.

Equipment

Provision of epidural analgesia for labour virtually always involves the insertion of an epidural catheter, usually with one of a variety of disposable epidural packs that are available. In the UK, these usually include a16G or 18G Tuohy epidural needle, a multiorifice catheter and a filter. Single, end-hole epidural catheters are popular in North America but are rarely used in the UK. Most epidural packs include a loss-of-resistance (LOR) syringe (strictly, called an LOR ‘device’ as they do not meet the standard for ‘syringes’) for identifying the epidural space.

If analgesia is to be provided by continuous infusion or patient-controlled epidural analgesia (PCEA), a suitable infusion syringe or pump will be required. Dilute solutions of local anaesthetic and opioid for either intermittent top-up or infusion may be prepared ‘inhouse’ by the hospital pharmacy or may be purchased from an external manufacturer.

Technique

Epidural analgesia is traditionally commenced at or near the onset of established labour. However, it may be initiated earlier, for example before induction of labour or in those with significant risk factors such as morbid obesity or an unfavourable airway. Women who request epidural analgesia in advanced labour may have difficulty in adopting or maintaining the desired position for epidural placement, which may be challenging for the anaesthetist. These patients should be advised that delivery may precede the onset of effective labour analgesia.

Either a midline or a paramedian technique may be used to approach the epidural space. Both techniques are equally possible and acceptable in the lumbar spine, and the final choice of approach is usually determined by personal preference.

The epidural space is usually identified by LOR to the injection of saline, using a continuous injection technique. Although previously popular, because the presence of clear fluid must indicate dural puncture, the use of LOR to air is no longer advocated, as this is associated with a number of disadvantages including patchy block, subcutaneous emphysema, pneumocephalus and air embolism.

The continuous technique involves the operator’s hand exerting a continuous pressure on the syringe plunger as the needle is advanced. Because saline is non-compressible, when the needle tip lies in the ligament or the ligamentum flavum there will be resistance to injection, which is lost as the epidural space is entered. With the intermittent technique, usually with air, the plunger is tested after each incremental advance of the needle. However, this technique is used less now as air is not routinely used for LOR; it is also thought that the intermittent technique may be associated with a higher incidence of dural puncture.

Once the epidural space has been identified, the epidural catheter is inserted through the needle, leaving 3-5 cm within the epidural space, and is secured to the mother’s back. With shorter lengths inserted, the spread of the block is usually better, but there is a greater chance of the catheter falling out; longer lengths are associated with lower replacement rates but more one-sided blocks.

Ultrasound has been used to assist in locating the epidural space, for example by identifying the midline and/or depth of space before needle insertion. A number of studies have established that there is a considerable degree of error when manual palpation is used to identify the desired intervertebral level for neuraxial blockade. Insertion of a spinal needle at a higher space than intended carries the potential risk of injury to the conus. In addition, patients with impalpable bony landmarks or structural deformity of the spine may be exposed to additional risks associated with repeated punctures or failure to establish regional anaesthesia. Pre-procedural ultrasonography enables the operator to determine the optimal site for puncture and the needle trajectory, and allows a reliable estimation of the depth of the epidural space, which may reduce the number of attempts required for successful placement of a central neuraxial block.

Although the ultrasound-guided technique has established advantages, it is not without its limitations. Image acquisition may be challenging in obese patients, and there remains a margin of error in the identification of intervertebral levels, albeit smaller than that with clinical assessment. Learning the technique requires consistent practice, ideally in routine cases. It has been suggested that competency in neuraxial scanning may be achieved after the performance of a minimum of 30-40 scans.

Epidural drugs

In the 1970s and 1980s, the only drug used widely in the UK to provide epidural analgesia was bupivacaine, used in concentrations of 0.25-0.5%. During the past 30-40 years a variety of drug mixtures has been assessed. The most commonly used combination in the UK is now bupivacaine and fentanyl (0.1-0.125% bupivacaine with 2-2.5 pg/ml fentanyl). The reason for adding opioids to local anaesthetic is to enhance the quality of analgesia and to reduce the total dose of local anaesthetic given, with the intention of reducing both motor block and rates of instrumental vaginal delivery.

In North America, combinations of up to four drugs (bupivacaine, sufentanil, adrenaline and clonidine) have been recommended, but the benefit of using such mixtures, given the potential for drug errors, has been questioned. More recently, levobupivacaine (0.1-0.125%) or ropivacaine (0.2%) has been used alone or in combination with opioids.

These ‘low-dose’ mixtures are given as intermittent top-ups of 10-15 ml, infusions of 10-12 ml/hour, or PCEA. For the latter, several different methods have been described, but typical regimens consist of boluses of 8-15 ml with no background infusion, or boluses of 4-6 ml with a background infusion of 4-8 ml/hour. Suitable lockout periods are 5-20 minutes.

Infusions and PCEA have been shown to have similar efficacy to intermittent boluses, although the two former techniques have been associated with better maternal satisfaction and a lower workload for staff. The main advantages of PCEA techniques are the reduced consumption of local anaesthetic, and therefore reduced motor blockade, and improved patient satisfaction as mothers are also in control of their pain relief.

Recently, more sophisticated methods of drug delivery have been explored. These include programmed intermittent bolus administration (in which mandatory boluses are given, e.g. 10 ml low-dose solution every 30 minutes, instead of boluses on demand) and computer-integrated PCEA (in which basal infusion rates are adjusted according to the woman’s demands/usage during the previous hour). A ‘programmed intermittent mandatory bolus’ technique has also been described, in which mandatory boluses are given unless the woman has received a self-administered bolus within a set time frame. Such techniques have been developed with the aim of reducing drug requirements and/or improving the quality of analgesia. They currently require sophisticated equipment and are not widely used.

Side effects and complications of epidural analgesia

Epidural analgesia is highly effective but is an invasive technique that has associated side effects and the potential for life-threatening complications (Table 26.1). It must not, therefore, be used unless there is adequate care from a suitably trained birth attendant and the ability to access advanced resuscitation facilities rapidly if required.

Epidural local anaesthetics cause sympathetic blockade and hypotension. Administration of intravenous fluids, vasopressor agents, or a combination of both, can prevent and/or treat this. Currently used low-dose combinations of local anaesthetic and opioid cause minimal haemodynamic disturbance, but it is mandatory to establish venous access before initiating epidural analgesia, although routine preloading with intravenous fluids has been abandoned in many units unless there are other indications such as dehydration.

Table 26.1 Risk of side effects and complications of epidural analgesia

Local anaesthetics also cause motor blockade, commonly graded by using various versions of the Bromage score (Table 26.2). The scoring system has been modified several times from the original one, described in 1965, to account for the less intense motor block that occurs with modern, low-dose techniques. Because such variety of scores exists, it is important that staff are familiar with the system in use in their unit. Motor blockade can be minimised by using the lowest concentration of local anaesthetic compatible with adequate analgesia. Addition of opioid facilitates reduction of local anaesthetic dose, but motor blockade may still occur.

Epidural opioids may cause nausea, vomiting, urinary retention, itching and respiratory depression. Each of these side effects occurs less commonly with fentanyl than with other opioids.

The effect of epidural opioids on gastric emptying is uncertain. Boluses of fentanyl (50-100 µg) have been shown to delay gastric emptying by up to 45 minutes, but low-dose continuous infusions do not appear to have this effect.

There has been considerable debate about the effect of epidural analgesia on the outcome of labour. Meta-analysis suggests that epidural analgesia may prolong the second stage of labour, with a resultant increase in the need for instrumental delivery, but not caesarean section.

Table 26.2 Bromage score for assessing motor power following epidural analgesia

Key points

• Most units in the UK offer a 24-hour epidural service for labour.

• Modern techniques consist of low-dose local anaesthetic (usually bupivacaine) with opioid (usually fentanyl in the UK and fentanyl or sufentanil elsewhere).

• PCEA techniques are associated with reduced usage of local anaesthetic.

• Use of epidural analgesia may prolong the second stage of labour and increase the likelihood of instrumental delivery.

Further reading

Anim-Somuah M, Smyth RM, Cyna AM, Cuthbert A. Epidural versus non-epidural or no analgesia for pain management in labour. Cochrane Database Syst Rev 2018; (5): CD000331.

Loubert C, Hinova A, Fernando R. Update on modern neuraxial analgesia in labour: a review of the literature of the last 5 years. Anaesthesia 2011; 66: 191-212.

Sng BL, Sia ATH. Maintenance of epidural labour analgesia: the old, the new and the future. BestPract Res Clin Anaesthesiol 2017; 31: 15-22.