FRCA Notes

Caudal Epidural Anaesthesia

The core curriculum asks us to describe 'how pain-relief is provided for children undergoing surgery including the use of common regional techniques e.g. caudal epidural'.

The topic was a CRQ in 2024 was 'generally well answered' and included components on anatomy, indications and contraindications.

Resources

  • Caudal epidurals were historically commonly used in paediatric patients for infra-umbilical surgery
  • However, there are now alternative regional anaesthetic techniques which:
    • Are equivalent or superior in quality and duration of analgesia, and
    • Don't require neuraxial needling, and
    • Don't cause lower limb motor block

  • May be used:
    • As a supplement to GA for intra-operative analgesia
    • For post-operative analgesia
    • In the management of acute and chronic lower abdominal and back pain
  • Patient or parent refusal
  • Overlying infection e.g. pilonidal cyst
  • Allergy to local anaesthetic
  • Coagulopathy
  • Anatomical abnormality e.g. spina bifida, raised ICP, fractures of the sacrum, sacral agenesis, tethered cord syndrome

Analgesia

  • Caudal analgesia is produced by injecting LA into the caudal canal, anaesthetising:
    • S2 → skin of posterior legs | bladder | gluteus maximus | flexor hallucis longus
    • S3 - 5 posterior rami → skin over buttocks
    • ± lumbar nerve roots

Sacral bone anatomy

  • The sacrum is a triangular bone that articulates with the fifth lumbar vertebra, the coccyx and the ilia
  • The dorsal roof consists of the fused laminae of the five sacral vertebrae and is convex dorsally
  • In the midline is a median crest which represents the sacral spinous processes
  • Lateral to this is the intermediate sacral crest with a row of four tubercles which represent the articular processes
  • The S5 processes are remnants and form the cornua, which provide the main landmarks for identifying the sacral hiatus

The sacral hiatus

  • The sacral hiatus is identified by the tip of an equilateral triangle drawn between the PSIS
  • The hiatus is covered by the sacro-coccygeal membrane, which is in continuity of the ligamentum flavum
  • The sacral hiatus leads to the sacral canal, a triangular shaped canal that is a continuation of the lumbar spinal canal

Contents of the sacral canal

  • Nerves
    • Cauda equina (S1 - S5 and Co1) and filum terminale
    • The spinal cord typically ends at L1/2 (L3 in infant)

  • The spinal meninges (subarachnoid and subdural spaces) i.e. the dura, typically end at S2
  • Areolar connective tissue
  • Fat, which fibroses with increasing age, making the block less reliable once >7yrs
  • Lymphatics
  • Venous plexus: Batson's plexus is a network of valveless veins, connecting the deep pelvic and thoracic veins to the vertebral venous plexus

Landmark

  • Patient anaesthetised
  • Left lateral positioning, knees drawn up to chest
  • Identify sacral hiatus
    • Lies at the point of an equilateral triangle drawn between the PSIS
    • Cornua are palpated either side of the sacral hiatus

  • Aseptic approach
  • A 22G cannula is inserted at 45°
    • Click/'pop' felt as passes through sacrococcygeal membrane
    • Then angulated cranially and the catheter railroaded over the needle into the sacral canal

  • Aspirate to ensure no blood or CSF
    • Leave open to air for 3 minutes to ensure no CSF or blood returns
    • There should be minimal resistance to injection of LA

Ultrasound guidance

  • Aids visualisation of anatomical structures
  • Increases first puncture success rate
  • Does not increase overall success rate
  • Reduces risk of subcutaneous or vascular injection
  • May increase time for block performance

Paediatrics

  • 0.25% levobupivcaine; levobupivacaine superior to bupivacaine as less motor block and less neuro-/cardio-toxicity

  • Doses classically described by Armitage:
    • Sacro-lumbar block → 0.5ml/kg (e.g. circumcision, orchidopexy)
    • Upper abdominal block → 1ml/kg (e.g. inguinal hernia)
    • Mid-thoracic block → 1.2ml/kg [NB exceeds usual recommended maximum dose of 1ml/kg]
  • NB ESRA recommends a maximum dose of 1ml/kg

  • 0.2% ropivacaine is an alternative

Adults

  • 20-30ml of 0.25% or 0.5% (levo)bupivacaine
  • There is less spread of LA in adults due to more densely packed and fibrous epidural fat in adults

Adjuncts; non-opioid

  • Both clonidine and preservative-free ketamine increase the duration of analgesia by 5 - 10hrs
  • They can, however, increase risk of sedation, apnoea or nausea and should be avoided in day case surgery
  • Doses:
    • Clonidine 0.5 - 2μg/kg
    • Preservative-free ketamine 0.5mg/kg

Adjuncts; opioid

  • Fentanyl 1-2μg/kg
    • Does not prolong the duration of analgesia
    • Significantly increases the incidence of PONV and should be avoided in day case surgery

  • Long-acting opioids increase the duration of analgesia by 24hrs
  • However, they commonly cause nausea or pruritus and carry the risk of delayed respiratory depression
  • They should therefore be avoided in day case surgery
  • Examples include:
    • Morphine 50μg/kg
    • Diamorphine 30μg/kg
Adjunct Dose
Clonidine 0.5 - 2μg/kg
Dexmedetomidine 0.5 - 1μg/kg
Preservative-free ketamine 0.5mg/kg
Fentanyl 1 - 2μg/kg
Morphine 10-30μg/kg
Diamorphine 30μg/kg


  • Complications are rare overall (1.9%)
Complications of caudal epidural
Failure (1%) inc. subcutaneous injection
LA toxicity from intravascular injection (0.02%)
Spinal anaesthesia from intrathecal injection
Infection ± epidural abscess
Motor blockade
Hypotension
Urinary retention and need for catheter
Accidental needle insertion into rectum or periosteum