Epidural Analgesia

• What is Epidural Analgesia?
• What is Epidural Analgesia used for?
• How does Epidural Analgesia work?
• Types of analgesia used in Epidural Analgesia
• Important issues regarding the Epidural Analgesia
• Complications
• Neurological Complications
• Summary

What is Epidural Analgesia?

Epidural analgesia is an injection of local anaesthetic alone, or more commonly in combination with pain. The injection is usually made in the lumber region at the L2/3 or L3/4 space.

What is Epidural Analgesia used for?

Epidural analgesia provides a reliable and excellent analgesia during childbirth without resulting in concomitant maternal or foetal central depression seen with systemic opioids. In most centres, a combination of local anaesthetic and opioid is administered via the epidural catheter. This method improves pain control, uses a smaller dose of either drug, and therefore has fewer side effects. Epidural analgesia is indicated for several obstetric situations such as:

• Prolonged labour
• Difficult forceps delivery
• Maternal exhaustion during labour
• Pre-eclampsia
• Unacceptable pain during labour

How does Epidural Analgesia work?

Epidural analgesia provides complete motor (causing paralysis) and sensory blockade (causing loss of sensation), around or near the site of pain. The level of epidural block usually extends distal from the upper abdomen. As a consequence of epidural analgesia; women become immobile and require more frequent observations by a midwife.

Types of analgesia used in Epidural Analgesia

There are different types of analgesia used in epidural analgesia, for instant the local anaesthetics and or opioids.

Epidural Local Anaesthetics
Some examples of local anaesthetics include bupivacaine hydrochloride, ropivacaine hydrochloride and lignocaine hydrochloride.

• Bupivacaine hydrochloride: Bupivacaine is a local anaesthetic that stabilises the neuronal membrane and prevents the initiation and transmission of nerve impulses. This drug is very potent, four times that of lignocaine, and has a rapid onset of anaesthesia with prolonged duration of action. Bupivacaine is suitable for continuous epidural blockade.
• Ropivacaine hydrochloride: This drug also behaves in the same manner as bupivacaine with exception that ropivacaine has both anaesthetic and analgesic effects. At higher doses it produces surgical anaesthesia with motor block, while at lower doses it produces a sensory block, including analgesia, with little motor block.
• Lignocaine hydrochloride: This medicine has the same mechanism of anaesthetic action to that of bupivacaine and ropivacaine.

Epidural opioids
The lipid solubility of opioids influences its onset and duration of action. Lipophilic (fat soluble) opioids, such as fentanyl, are able to penetrate the dura or the arachnoid membranes and spinal tissues resulting in a rapid onset of analgesia, but a limited duration. On the other hand, hydrophilic (water soluble) drugs such as morphine have slow diffusion rate in the spinal membrane, thus slower onset of action and longer duration.

• Morphine: is an opioid with sedative properties used to relieve severe or constant pain such as childbirth pain, which cannot be controlled by any other pain relievers. Morphine exerts its analgesic effects by acting as an agonist and activating the opioid receptors in both the central and peripheral nervous systems; In doing so, the pain threshold is elevated and the brain’s awareness of the pain is decreased.
• Fentanyl: The principal actions of fentanyl are analgesia and sedation. It exerts its effects by acting on specific opioid receptors in the brain, through which they block the pain messages being delivered. In doing so, fentanyl decreases the brain’s awareness of the pain and provides pain relieve to the patient. Like any other analgesics, fentanyl produces respiratory depression, drowsiness, sedation and constipation.

Important issues regarding the Epidural Analgesia

Prior to administration of epidural analgesia you must provide consent and tell your doctor, anaesthetist or gynaecologist if you have:

• History of hypersensitivity or allergy to any previous medications including anaesthetics and opioids
• Local inflammation or infection
• Spinal deformity or previous spinal surgery
• Bleeding or clotting disorders
• Cardiovascular disease/s such as heart failure, cardiac ischemia, hypertension or hypotension and/or any other cardiac complications
• Nervous system disease
• Neuromuscular disease such as myasthenia gravis
• Any other medical conditions

In addition, if you are taking any medication/s, you must inform your doctor prior to the procedure. This is because some local anaesthetics and opioids can interact with other medications, resulting in unwanted or serious complications.

Complications of Epidural Analgesia

Local anaesthetics are generally safe if used in recommended doses. However, most complications are related to the techniques, resulting in systemic toxicity, or to the effects of the block, rather than to the drugs used. In comparison, epidural opioids provide complete blockage of muscle and sensation, resulting in women becoming immobile and requiring more frequent observations by a midwife. They will also require a catheter to avoid urinary retention.

Central Nervous System Complications

• Local anaesthetic, possibly after accidental and unintentional injection, is one cause of convulsion or seizures in the labour ward. Although your doctor will take into consideration other causes of this symptoms, for instance, high blood pressure, water retention due to oxytocin (a mammalian hormone released during childbirth) toxicity, pre-existing epilepsy, low blood sugar in diabetics, infections.

Management Strategies
In case of CNS toxicity, the doctor and anaesthetist take the following measures:

• Maintain airway and ensure oxygenation
• Ventilation if necessary
• Protect the airway from aspiration by placing a tube in the airway tract
• Implement appropriate anticonvulsant therapy, such as diazepam, clonazepam, thiopentone, if seizure is prolonged
• Review any other potential causes and enact treatment accordingly
• Liase with the obstetrician regarding urgent delivery

Cardiovascular System
Vascular system complications are characterised by hypotension (low blood pressure), arrythmias (disturbed rhythm of the heart), and heart attack. Management of Hypotension: If a fall in blood pressure has been noticed, the doctor takes the following measures:

• Check the blood pressure manually
• Elevate legs
• Ensure adequate oxygenation
• Position the patient on the side and administer a rapid infusion of fluid under instruction of anaesthetist
• If pregnant women, the maternal blood pressure and foetal heart rate should be monitored closely. If the hypotension is an ongoing problem, ephedrine sulfate is used.

Neurological Complications

Some examples of neurological complications include total spinal anaesthesia (TSA), high block and postdural puncture headache.

Total Spinal Anaesthesia
Total spinal anaesthesia (TSA), which occurs when the injection has been given unintentionally at the wrong site, is a rare but serious complication. TSA is characterised by sudden hypotension, rapidly increasing motor block, temporarily loss of breathing, loss of consciousness, dilated pupils, and is preceded by respiratory distress due to the blockade of some nerve cells. Management Strategies: The doctor and anaesthetist take the following measures:

• Maintain airway and ensure oxygenation and position the patient on the side to prevent aspiration of secretions
• Ventilation with a bag or mask
• Protect the airway from aspiration by placing a tube in the airway tract
• Treat hypotension with appropriate medications such as ephedrine
• Treat slowing of the heart with appropriate medications
• Loss of consciousness and dilated pupils should resolve once the respiratory and cardiovascular systems are supported
• In the pregnant women, the foetus should be monitored closely and urgent delivery may be required if the foetal distress is severe and/ or resuscitation in difficult.

High Block
Symptoms associated with high block are nasal stiffness and difficulty breathing. Management Strategies: If this occurs, the doctor takes the following measures:

• Reassure the patient and provide an explanation of what is happening
• Treat hypotension with appropriate medications such as ephedrine
• Treat slowing of the heart with appropriate medications
• Remain with the patient
• If the maternal blood pressure is low, help the mother to sit upright
• Monitor the foetal condition closely

Postdural Puncture Headache
Postdural puncture headache following accidental subarachnoid or spinal puncture during spinal anaesthesia is the commonest neurological complication of neural blockade. Postdural puncture headache usually develop 12 to 36 hours postpartum. This type of headache is characterised typically by a throbbing frontal pain, although it can occur elsewhere in the head and neck, and is relieved by lying flat which indicates that it has a postural component. Management Strategies: Your doctor will counsel you on the potential problems and management as well as monitoring you regularly. This type of headache often resolves soon, however if the headache re-develops, the following action is taken:

• Your doctor will encourage the intake of oral fluids and regular oral pain relieves as well as bed rest
• You doctor will perform a neurological examination in order to eradicate other causes of headache
• If you experiences nausea and vomiting, IV fluids may be required
• Oral caffeine to treat the postdural puncture headache might be considered

Summary

Pain during childbirth or caesarean surgeries:

• Epidural Analgesia
• Bupivacaine hydrochloride alone and/or in combination with opioids such as fentanyl or morphine
• Ropivacaine hydrochloride alone and/or in combination with opioids such as fentanyl or morphine
• Lignocaine hydrochloride alone and/or in combination with opioids such as fentanyl or morphine

References