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Evidence‐based approaches

Epidural analgesia is the administration of analgesics (local anaesthetics and opioids with or without adjuvants such as corticosteroids and clonidine) into the epidural space via an indwelling catheter (Macintyre and Schug [99]). This technique enables analgesics to be injected close to the spinal cord and spinal nerves, where they exert a powerful analgesic effect. Epidural analgesia can provide longer‐lasting pain relief with less dosing of opioids (Chou et al. [40]). It is one of the most effective techniques available for the management of acute pain (Chou et al. [40]) and is deemed the gold standard technique for managing pain after surgery (Bashandy and Elkholy [8]).
Intrathecal (spinal) analgesia is the administration of analgesic drugs directly into the CSF in the intrathecal space (Gélinas and Arbour [65]). Analgesic drugs given via this route are 10 times as potent as those given into the epidural space so the doses given are much smaller.
Spinal blocks are forms of anaesthesia that temporarily interrupt sensation from the chest, abdomen and legs by injection of local anaesthetic medication into the vertebral canal, which contains the spinal cord, spinal nerves and CSF. They are typically given as a single injection, which will last for 2–6 hours depending on the type and volume of local anaesthetic given. If an opioid is given, such as morphine, this can produce analgesia lasting 12 hours (Macintyre and Schug [99]). See the previous section for more information on spinal blocks.
In chronic cancer pain, intrathecal drug delivery (ITDD) can be used for the delivery of continuous infusions of analgesia in patients with spasticity and in patients with cancer pain that is uncontrolled with appropriate systemic opioids or when analgesia leads to intolerable side‐effects (British Pain Society [30], NHS England [121]).
In 2015, NHS England stopped commissioning ITDD fully implantable systems for patients with non‐cancer pain. Healthcare professionals should note that patients with chronic non‐cancer pain may have had an ITDD inserted prior to 2015 and they may continue to be managed by their specialist chronic pain service today (NHS England [121]). See the chapter on pain assessment and management in The Royal Marsden Manual of Cancer Nursing Procedures (Lister et al. [97]) for further information about using this device for cancer pain.

Rationale

There are three main advantages to using epidural analgesia:
  • It has the potential to provide effective dynamic pain relief for many patients (Rosero et al. [160]).
  • The combination of local anaesthetic agents with opioids has a synergistic action that allows the concentration of each drug to be reduced. This limits the unwanted side‐effects of each drug (McClymont and Celnick [107]).
  • There is evidence that the use of epidural analgesia may reduce the stress response (McClymont and Celnick [107]) to surgery or trauma, thereby reducing morbidity, recovery time and duration of hospital stay (Rosero et al. [160]).

Indications

Indications for epidural analgesia include the following:
  • provision of analgesia during labour
  • as an alternative to general anaesthesia, for example in severe respiratory disease or for patients with malignant hyperthermia
  • provision of post‐operative analgesia: epidural analgesia has been used since the late 1940s as a method of controlling post‐operative pain (Toledano and Tsen [176])
  • provision of analgesia for pain resulting from trauma, for example fractured ribs, which may result in respiratory impairment due to pain on breathing
  • management of chronic intractable pain in patients with chronic or cancer‐related pain who experience the following:
    • unacceptable side‐effects with systemic opioids
    • unsuccessful treatment with opioids via other routes despite escalating doses
    • severe neuropathic pain due to tumour invasion or compression of nerves (McSwain et al. [111])
  • to relieve muscle spasm and pain resulting from lumbar cord pressure due to disc protrusion or local oedema and inflammation.

Contraindications

These may be absolute or relative.

Absolute

Absolute contraindications for epidural analgesia include the following:
  • patients with coagulation defects, which may result in haematoma formation and spinal cord compression, for example iatrogenic (anticoagulated patient) or congenital (haemophiliacs), or thrombocytopenia due to disease (Harrop‐Griffiths et al. [74], Schug et al. [166])
  • local sepsis at the site of proposed epidural; the result might be meningitis or epidural abscess formation (Vayne‐Bossert et al. [188])
  • proven allergy to the intended drug
  • unstable spinal fracture
  • patient refusal to consent to the procedure.

Relative

Relative contraindications for epidural analgesia include the following:
  • unstable cardiovascular system
  • spinal deformity
  • raised intracranial pressure (a risk of herniation if a dural tap occurs)
  • certain neurological conditions, for example multiple sclerosis, where an epidural may result in an exacerbation of the disease (McSwain et al. [111])
  • unavailability of staff trained in the management of epidural analgesia (Macintyre and Schug [99]): it is identified that epidural analgesia carries specific risks and it is recommended that staff undertake a period of formal training in this area to enable them to care for patients safely and competently (Schug et al. [166]).

Methods of administration

Continuous infusion

Continuous infusions of epidural drugs are the most effective way of providing dynamic pain relief after major surgical procedures (Argoff [5]). The epidural is placed near to the site of the surgery to achieve the optimum analgesic effect (RCA [150]).
Continuous infusions can be given via either a syringe pump or a designated infusion pump system. The effectiveness of this method of administering drugs is dependent on a number of factors, including the combination of drugs used, whether the catheter is positioned at a level appropriate to the site of the surgery or pain (Kooij et al. [89], RCA [150]) and the volume of the local anaesthetic agent infused (Chou et al. [40]).

Patient‐controlled epidural analgesia

The use of patient‐controlled epidural analgesia (PCEA) enables patients to control their analgesia (Schug et al. [166], Tiippana et al. [175]). For post‐operative patients, PCEA can provide greater analgesia efficacy in combination with a low‐dose background infusion (Jules‐Elysee et al. [87], Tiippana et al. [175]). This ensures a baseline level of analgesia, which can then be supplemented by the patient when required (Jules‐Elysee et al. [87]).

Bolus injections

Bolus injections of local anaesthetic agents and/or opioids are used infrequently to manage post‐operative pain but are more commonly used for managing labour pain (Bujedo [33]). This procedure is usually performed by a doctor. However, bolus doses of low‐dose concentrations may be given by nursing or midwifery staff as part of an advanced practice role, according to local policy. This should follow an agreed period of education and supervised practice, which must be documented.
This is a clean, aseptic procedure. Most epidural infusion pumps allow a bolus dose to be programmed and delivered from the pump. This prevents the administration line and bacterial filter being accessed and thus minimizes the risk of introducing infection.

Classes of epidural and intrathecal drugs and mechanism of action

Three classes of drugs are commonly used to provide epidural analgesia: opioids, local anaesthetic agents, and adjuvant drugs such as corticosteroids and clonidine.

Opioids

The two opioids most commonly used for epidurals are diamorphine and fentanyl (Gorlin et al. [69]). When either of these opioids is injected into the epidural space, part of the opioid dose:
  • crosses the dura and arachnoid membrane and enters the CSF; from the CSF, a proportion of the drug is taken up into the spinal cord and reaches the opioid receptors in the spinal cord; once bound to the opioid receptors, pain impulses are blocked
  • enters the systemic circulation and contributes to analgesia
  • binds to the epidural fat and does not contribute to analgesia.
In contrast, when opioids are placed directly into the CSF in the intrathecal space, they attach directly to the opioid spinal cord receptor sites (Nolan [130]). In acute pain, spinal intrathecal analgesia is usually given in a monitored environment (e.g. critical care or a high‐dependency unit).
Fentanyl differs from diamorphine in that it is more lipid soluble (Gorlin et al. [69]). This means that it passes more easily into the CSF, and so gains faster access to the opioid receptors and has a more rapid onset of action. Fentanyl also has a shorter duration of action (1–4 hours) compared to diamorphine (6–12 hours) (Macintyre and Schug [99]).

Local anaesthetic drugs

As for regional blocks, commonly used local anaesthetic agents for epidural analgesia include bupivacaine, levobupivacaine and ropivacaine. They inhibit pain transmission by blocking sodium ion channels, which are involved in the propagation of electrical impulses along the spinal nerves. In epidural analgesia, these drugs gain access to the nerve roots and the spinal cord by crossing the dura and subarachnoid membranes (Gélinas and Arbour [65]).
The dose of a local anaesthetic agent will also determine which nerves are blocked. Low concentrations of bupivacaine (e.g. 0.100– 0.125%) preferentially block nerve impulses in the smallest‐diameter nerve fibres, which include the pain and temperature sensory fibres. As the larger‐diameter motor fibres are less likely to be blocked with concentrations of 0.100–0.125% bupivacaine, the incidence of leg weakness is reduced and patients are able to mobilize.

Adjuvant drugs

Clonidine is an example of an adjuvant drug that can be used to provide epidural analgesia. It is a mixed alpha‐adrenergic agonist. Alpha‐2 adrenoceptor agonists act as analgesics at the level of the dorsal horn of the spinal cord, although there may be peripheral effects as well (Nguyen et al. [120]). Clonidine is believed to enhance analgesia provided by spinal opioids and local anaesthetic drugs, and additionally may reduce post‐operative systemic opioid requirements (Gallagher and Grant [63], Schug et al. [166]). Systemic adverse effects predominantly consist of centrally mediated sedation and hypotension.
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