Overview

Regional anaesthesia involves blocking nerve conduction to produce a reversible loss of sensation in a specific body region.

It is an umbrella term that includes peripheral and neuraxial blocks:

• Neuraxial blocks (epidural or spinal anaesthesia): involve injecting local anaesthetic near the spinal cord
• Peripheral nerve block: involves injecting local anaesthetic into individual / plexus nerves

Epidural Anaesthesia

Definition

Epidural anaesthesia involves the administration of drugs (local anaesthetic +/- opioids) into the epidural space of the spine.

Technique

Epidural anaesthesia usually involves the placement of a catheter in the epidural space, allowing intermittent or continuous drug delivery (like an infusion).

An epidural can be performed at ANY spinal level, depending on where the block is desired

• This is because the needle is placed in the epidural space, where there is no risk of directly damaging the spinal cord.
• In contrast, spinal anaesthesia must be administered below the level of L2 to avoid the risk of spinal cord injury as the needle enters the subarachnoid space.

Effects

Epidural anaesthesia produces a segmental block of spinal nerve roots, affecting nerve fibres at specific spinal segments corresponding to the site of injection

The extent of the involved segment spinal nerve roots (i.e. how many spinal levels above and below the site of injection) depends on the volume and concentration of anaesthetic injected

• The block usually encompasses 4–8 spinal levels above and below the injection site

Epidural anaesthesia can block both sensory and motor function, but it depends on the concentration and dose administered:

• Sensory block is typically more prominent and occurs at lower doses and concentrations
• Differential blockade phenomenon: sensory fibres are blocked before motor fibres

Indications

Key indications for epidural anaesthesia:

• Labour analgesia
  • Epidural anaesthesia provides a differential block, often allowing effective sensory analgesia for labour pain relief with relative preservation of motor function. This helps maintain the mother’s ability to move and participate in the labour process.
• Open abdominal surgery
• Thoracic surgery

 

Epidural anaesthesia is also used for post-op pain control following abdominal and thoracic surgery (it is recommended over systemic opioids)

• The primary postoperative benefit of epidural anaesthesia is quicker return of bowel function in abdominal surgery and improved pulmonary outcomes in thoracic surgery

Contraindications

Key contraindications include:

• Active anticoagulation / coagulopathy (due to risk of epidural haematoma)
• Severe thrombocytopaenia
• Local infection (at the site of insertion)

Adverse Effects and Complications

Common side effects:

• Sympathetic blockage effects – hypotension, bradycardia, urinary retention
• Opioid-related effects – pruritus, nausea and vomiting

Less common side effects:

• Post-dural puncture headache (CSF leakage → reduced ICP)
  • Causes a typical orthostatic headache due to the low ICP (headache that is worse with sitting / standing and improves with lying down)
  • Other symptoms: visual disturbance, nausea, meningism
  • Management
    • 1st line: conservative management (oral hydration, analgesia, caffeine)
    • 2nd line (definitive): epidural blood patch
• Transient neurological symptoms

Rare but serious complications:

• Epidural haematoma (can cause spinal cord compression and permanent neurological damage)
• Epidural abscess / meningitis
• Direct nerve trauma

Spinal Anaesthesia

Definition

Spinal anaesthesia involves the administration of drugs (local anaesthetic +/- opioids) into the ​​​​​subarachnoid space of the spine.

Technique

Spinal anaesthesia involves a single injection (single-shot technique) of drugs into the subarachnoid space

• No catheter is placed, no continuous infusion of drugs
• Produces a rapid-onset blockage

single-shot technique

Effects

Spinal anaesthesia typically produces a uniform, dense block of sensory + motor + sympathetic fibres at the affected dermatomes

• This is different from the differential block in epidural, where sensory fibres are blocked before motor fibres

Spinal anaesthesia can block up to T4 and down to S5

• The injection site is always in the lumbar area (below L2) to avoid spinal cord injury
• The dose, volume, and type of the local anaesthetic agent determine the block height

Indications

Due to its single-shot property, it is used for short-to-moderate duration procedures

• Caesarean section
• Lower abdominal / pelvic surgery
• Lower limb surgery

Contraindications

Key contraindications include:

• Active anticoagulation / coagulopathy (due to risk of epidural haematoma)
• Severe thrombocytopaenia
• Local infection (at the site of insertion)

Additional contraindications for spinal anaesthesia (but not for epidural):

• Severe hypovolaemia / shock
• Raised ICP

Adverse Effects and Complications

Common side effects:

• Sympathetic blockage effects – hypotension, bradycardia, urinary retention
• Opioid-related effects – pruritus, nausea and vomiting

Less common side effects:

• Post-dural puncture headache (CSF leakage → reduced ICP)
• Transient neurological symptoms

Rare but serious complications:

• Spinal haematoma
• Spinal abscess / meningitis
• Spinal cord infarction / injury

Peripheral Nerve Block

Overview

There are numerous types of peripheral nerve blocks. The most commonly performed ones are outlined below:

Block type	Nerve(s) targeted	Relevant anatomy	Indications
Femoral nerve block	Femoral nerve (L2-L4)	Femoral triangle of the groin	Hip fracture Hip / knee surgery Anterior sthigh procedures
Adductor canal block	Saphenous nerve (pure sensory)	Adductor canal of the thigh	Knee surgery Anterior / medial leg and foot procedures
Sciatic nerve block	Sciatic nerve (L4-S3)	Gluteal region	Knee surgery Lower leg surgery Ankle surgery Foot surgery
Transverse abdominis plane (TAP) block	Thoracolumbar spinal nerves	The fascial plane between the internal oblique and transversus abdominis muscles	Abdominal surgery